0000875045-24-000009 | 10-K | XBRL Viewer

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Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
Employee Benefit Plans (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Germany
Defined Contribution Plan Disclosure [Line Items]
Employee benefit plan obligations	$ 46.5	$ 40.9
Periodic pension cost	3.6	5.9	$ 7.6
Germany \| Other (income) expense, net
Defined Contribution Plan Disclosure [Line Items]
Periodic pension cost	0.8	1.8	2.1
Switzerland
Defined Contribution Plan Disclosure [Line Items]
Unfunded net pension	51.5	49.9
Employee benefit plan obligations	239.6	193.7
Pension cost (reversal)	$ 17.6	$ 20.0	$ 21.5
Percentage Of Minimum Investment Return	1.75%	2.00%	1.00%
Switzerland \| Other (income) expense, net
Defined Contribution Plan Disclosure [Line Items]
Pension cost (reversal)	$ 5.1	$ 5.3	$ 3.5
Deferred Compensation Plan
Defined Contribution Plan Disclosure [Line Items]
Deferred compensation liability	$ 134.6	131.9
United States
Defined Contribution Plan Disclosure [Line Items]
Minimum qualifying age for employee benefit plan	21 years
Expenses related to savings plan	$ 55.9	$ 56.0	$ 58.4

Collaborative and Other Relationships - Other Arrangements (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended				3 Months Ended	12 Months Ended
	Aug. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Apr. 30, 2020	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Potential future milestone payments commitment to third party approximately					$ 5,100.0	$ 5,100.0
Share of net profit from sage therapeutics, percent					50.00%	50.00%
Research and development						$ 2,462.0	$ 2,231.1	$ 2,501.2
Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Global licensing collaboration, shares purchased, amount		$ 650.0
Global licensing collaboration, shares purchased (in shares)		6.2
Global licensing collaboration, purchase price per share (in dollars per share)		$ 104.14
Global licensing collaboration, development and commercial milestone payments		$ 1,600.0
Research and development expense asset acquired					$ 75.0
Collaboration profit (loss) sharing						4.7
Denali Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Global licensing collaboration, shares purchased, amount			$ 465.0
Global licensing collaboration, shares purchased (in shares)			13.0
Global licensing collaboration, purchase price per share (in dollars per share)			$ 34.94
Global licensing collaboration, development and commercial milestone payments			$ 1,100.0
Sangamo Therapeutics, Inc. Agreement
Collaborative arrangements and non-collaborative arrangement transactions
Global licensing collaboration, shares purchased, amount				$ 225.0
Global licensing collaboration, shares purchased (in shares)				24.0
Global licensing collaboration, purchase price per share (in dollars per share)				$ 9.21
InnoCare Pharma Limited (InnoCare) Agreement
Collaborative arrangements and non-collaborative arrangement transactions
Upfront and milestone payments made to collaborative partner	$ 125.0
Other research and discovery
Collaborative arrangements and non-collaborative arrangement transactions
Research and development						$ 4.1	$ 39.2	$ 89.1

Income Taxes - Accounting for Uncertainty in Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 606.4	$ 563.4	$ 75.7
Additions based on tax positions related to the current period	5.2	36.3	4.2
Additions for tax positions of prior periods	60.2	23.4	509.9
Reductions for tax positions of prior periods	(485.0)	(14.9)	(18.8)
Statute expirations	(2.1)	(1.6)	(3.2)
Settlement payment	(11.3)	(0.2)	(4.4)
Ending balance	$ 173.4	$ 606.4	$ 563.4

Collaborative and Other Relationships - Summary of Activity Related to Sangamo Therapeutics (Details) - Research and development - Sangamo Therapeutics, Inc. Agreement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 4.1	$ 19.1	$ 22.7
Expense reflected within statements of income	$ 2.4	$ 12.1	$ 14.6

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Tax credits	$ 252.8		$ 112.6
Inventory, other reserves and accruals	203.7		202.8
Intangibles, net	1,153.9		1,370.3
Neurimmune's tax basis in ADUHELM	0.0		470.3
IRC Section 174 capitalized research and development	570.8		271.8
Net operating loss	1,700.4		1,845.9
Share-based compensation	36.1		37.2
Other	293.3		280.7
Valuation allowance	(1,278.7)	$ (85.0)	(2,003.3)
Total deferred tax assets	2,932.3		2,588.3
Deferred tax liabilities:
Purchased inventory valuation step-up and intangible assets	(1,257.4)		(76.1)
Samsung Bioepis investment installments	(35.5)		(138.0)
GILTI	(1,136.9)		(1,002.0)
Tax credits	0.0		(228.7)
Depreciation, amortization and other	(215.7)		(251.8)
Total deferred tax liabilities	$ (2,645.5)		$ (1,696.6)

Restructuring - Restructuring Reserve Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Reserve [Roll Forward]
Expense	$ 218.8	$ 131.1	$ 0.0
Workforce Reduction
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning	35.9	0.0
Expense	181.6	112.6
Payment	(140.5)	(78.0)
Foreign currency and other adjustments	(1.6)	1.3
Restructuring reserve, ending	$ 75.4	$ 35.9	$ 0.0

Investments in Variable Interest Entities

12 Months Ended

Dec. 31, 2023

Investments in Variable Interest Entities [Abstract]

Investments in Variable Interest Entities


Note 20:			Investments in Variable Interest Entities

Consolidated Variable Interest Entities

Our consolidated financial statements include the financial results of variable interest entities in which we are the primary beneficiary. The following are our significant variable interest entities.

Neurimmune SubOne AG

Beginning in 2007 we consolidated the results of Neurimmune as we determined we were the primary beneficiary because we had the power through the collaboration to direct the activities that most significantly impacted the entity's economic performance and we were required to fund 100.0% of the research and development costs incurred in support of the collaboration. The collaboration and license agreement with Neurimmune was for the development and commercialization of antibodies for the potential treatment of Alzheimer's disease, including ADUHELM (as amended, the Neurimmune Agreement).

In November 2023 we notified Neurimmune of our decision to terminate the Neurimmune Agreement. Subsequent to the termination, we reconsidered our relationship with Neurimmune and determined that we were no longer the primary beneficiary of the variable interest entity. As a result, we recorded a net gain on the deconsolidation of Neurimmune of approximately $3.0 million, which was recorded in other (income) expense, net within our consolidated statements of income for the year ended December 31, 2023.

In June 2021 ADUHELM was granted accelerated approval by the FDA. Under the terms of the Neurimmune Agreement, we were required to pay Neurimmune a milestone payment of $100.0 million related to the launch of ADUHELM in the U.S. During the second quarter of 2021 we made this $100.0 million payment, which was recognized as a charge to net income (loss) attributable to noncontrolling interests, net of tax in our consolidated statements of income. In addition, during the second quarter of 2021 we recognized net profit-sharing income of $45.0 million to reflect Eisai's 45.0% share of the $100.0 million milestone payment, which was recognized in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income.

During 2021 we recorded a net deferred tax asset in Switzerland of approximately $100.0 million on Neurimmune's tax basis in ADUHELM, the realization of which was dependent on future sales of ADUHELM. During the first quarter of 2022, upon issuance of the final NCD related to ADUHELM, we recorded an increase in a valuation allowance of approximately $85.0 million to reduce the net value of this deferred tax asset to zero. These adjustments to our net deferred tax asset were each recorded with an equal and offsetting amount assigned to net income (loss) attributable to noncontrolling interests, net of tax in our consolidated statements of income, resulting in a zero net impact to net income attributable to Biogen Inc.

Excluding the impact of the Neurimmune deferred tax asset, the assets and liabilities of Neurimmune are not significant to our consolidated financial position or results of operations as it is a research and development organization. We have provided no financing to Neurimmune other than contractually required amounts.

Research and development costs for which we reimbursed Neurimmune are reflected in research and development expense in our consolidated statements of income. For the years ended December 31, 2023, 2022 and 2021, amounts reimbursed were immaterial.

For additional information on our collaboration arrangements with Eisai, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Unconsolidated Variable Interest Entities

We have relationships with various variable interest entities that we do not consolidate as we lack the power to direct the activities that significantly impact the economic success of these entities. These relationships include investments in certain biotechnology companies and research collaboration agreements.

As of December 31, 2023 and 2022, the carrying value of our investments in certain biotechnology companies representing potential unconsolidated variable interest entities totaled $16.4 million and $27.8 million, respectively. Our maximum exposure to loss related to these variable interest entities is limited to the carrying value of our investments.

We have also entered into research collaboration agreements with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and

development expense in our consolidated statements of income as they are incurred. We have provided no financing to these variable interest entities other than previous contractually required amounts.

Dispositions

12 Months Ended

Dec. 31, 2023

Divestitures [Abstract]

Dispositions


Note 3:			Dispositions

Sale of Joint Venture Equity Interest in Samsung Bioepis

In April 2022 we completed the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics in exchange for total consideration of approximately $2.3 billion. Under the terms of this transaction, we received approximately $1.0 billion in cash at closing, with approximately $1.3 billion in cash to be deferred over two payments. The first deferred payment of $812.5 million was received in April 2023 and the second deferred payment of $437.5 million is due at the second anniversary of the closing of this transaction in April 2024.

Prior to the sale, the carrying value of our investment in Samsung Bioepis totaled $581.6 million. For the year ended December 31, 2022, we recognized a pre-tax gain of approximately $1.5 billion related to this transaction, which was recorded in other (income) expense, net in our consolidated statements of income. This pre-tax gain included reclassifications from AOCI to net income of approximately $58.9 million in cumulative translation losses, partially offset by approximately $57.0 million in gains resulting from the termination of our net investment hedge.

We concluded that the divestment of Samsung Bioepis did not meet the criteria to be reported as discontinued operations in our consolidated financial statements, as our decision to divest this business did not represent a strategic shift that would have a major effect on our operations and financial results.

We elected the fair value option and measured the payments due to us from Samsung BioLogics at fair value. As of December 31, 2023, the estimated fair value of the remaining second deferred payment using a risk-adjusted discount rate of 5.8% was approximately $430.0 million. This payment has been classified as a Level 3 measurement and is reflected in other current assets within our consolidated balance sheets as of December 31, 2023.

For the year ended December 31, 2023, we recognized a gain of approximately $13.7 million to reflect the change in fair value related to the first deferred payment due to us, which was received in April 2023. Additionally, for the year ended December 31, 2023, we recognized a gain of approximately $24.6 million to reflect the change in fair value related to the second deferred payment due to us. For the year ended December 31, 2022, we recognized a gain of approximately $10.7 million and a loss of approximately $1.4 million to reflect the changes in fair value related to the first and second deferred payments due to us, respectively. These changes were recorded in other (income) expense, net within our consolidated statements of income.

As part of this transaction, we are also eligible to receive up to an additional $50.0 million upon the achievement of certain commercial milestones. Our policy for contingent payments of this nature is to recognize the payments in the period the payments become realizable, which is generally the same period in which the payments are earned.

If any payments due to us remain outstanding after the second anniversary of the closing of this transaction, we may elect to receive shares of Samsung BioLogics common stock at a 5.0% discount in lieu of a cash payment for the remaining amount due. Currently, we believe that the likelihood of Samsung BioLogics failing to make the second deferred payment due to us is remote.

Additionally, for the year ended December 31, 2022, we recorded a discrete tax expense of approximately $257.9 million related to this transaction, which is reflected in income tax (benefit) expense in our consolidated statements of income.

Share-Based Payments - Time-Vested Restricted Stock Units Activity (Details) - RSUs - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares
Beginning balance, unvested (in shares)	1,946,000
Granted (in shares)	1,171,000
Vested (in shares)	(822,000)
Forfeited (in shares)	(439,000)
Ending balance, unvested shares (in shares)	1,856,000	1,946,000
Weighted Average Grant Date Fair Value
Beginning balance, unvested (in dollars per share)	$ 237.90
Granted (in dollars per share)	282.92	$ 221.28	$ 276.90
Vested (in dollars per share)	249.12
Forfeited (in dollars per share)	257.66
Ending balance, unvested (in dollars per share)	$ 256.74	$ 237.90
Number of shares granted (in shares)	1,171,000
Director
Shares
Granted (in shares)	7,300
Weighted Average Grant Date Fair Value
Number of shares granted (in shares)	7,300

Acquisitions Preliminary Purchase Price Allocation (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Sep. 27, 2023	Sep. 26, 2023	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Goodwill	$ 6,219.2	$ 6,219.2			$ 5,749.0	$ 5,761.1
Reata Pharmaceuticals, Inc
Business Acquisition [Line Items]
Cash and cash equivalents	267.3	267.3		$ 267.3
Accounts receivable	15.9	15.9		15.9
Inventory	1,259.0	1,259.0	$ 1,300.0	1,692.0
Measurement Period Adjustments, Inventory	31.5	(433.0)
Other current assets	53.6	53.6		53.6
Operating lease assets	121.2	121.2	121.2	122.4
Measurement Period Adjustments, Operating lease assets		(1.2)
Accrued expense and other	(101.5)	(101.5)		(98.9)
Measurement Period Adjustments, Accrued expense and other		(2.6)
Debt payable	(159.9)	(159.9)		(159.9)
Contingent payable to blackstone	(300.0)	(300.0)		(300.0)
Deferred tax liability	(912.4)	(912.4)		(922.5)
Measurement Period Adjustments, Deferred tax liability		10.1
Operating lease liabilities	(151.8)	(151.8)	(151.8)	(151.8)
Other assets and liabilities, net	(2.5)	(2.5)		(2.0)
Measurement Period Adjustments, Other assets and liabilities, net		(0.5)
Total identifiable net assets	6,728.9	6,728.9		6,136.1
Measurement Period Adjustments, Total identifiable net assets		592.8
Goodwill	464.5	464.5	464.5	1,057.3
Measurement Period Adjustments, Goodwill		(592.8)
Total assets acquired and liabilities assumed	7,193.4	7,193.4		7,193.4
Reata Pharmaceuticals, Inc \| Completed technology for SKYCLARYS (U.S.)
Business Acquisition [Line Items]
Intangible assets:	4,200.0	4,200.0	4,200.0	3,600.0
Measurement Period Adjustments, Intangible assets:		600.0
Reata Pharmaceuticals, Inc \| In-process research and development
Business Acquisition [Line Items]
Intangible assets:	2,300.0	2,300.0	2,300.0	1,900.0
Measurement Period Adjustments, Intangible assets:		400.0
Reata Pharmaceuticals, Inc \| Priority review voucher
Business Acquisition [Line Items]
Intangible assets:	100.0	100.0		100.0
Reata Pharmaceuticals, Inc \| Other clinical programs
Business Acquisition [Line Items]
Intangible assets:	$ 40.0	40.0	$ 40.0	$ 20.0
Measurement Period Adjustments, Intangible assets:		$ 20.0

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2023	Feb. 12, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	0-19311
Entity Registrant Name	BIOGEN INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0112644
Entity Address, Address Line One	225 Binney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	679-2000
Title of 12(b) Security	Common Stock, $0.0005 par value
Trading Symbol	BIIB
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 41,190,868,800
Entity Common Stock, Shares Outstanding		145,360,798
Documents Incorporated by Reference	Portions of the definitive proxy statement for our 2024 Annual Meeting of Stockholders are incorporated by reference into Part III of this report.
Entity Central Index Key	0000875045
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Derivative Instruments - Summary of the Effect of Derivatives Designated as Cash Flow Hedging Instruments (Details) - Foreign exchange contract - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)	$ 11.6	$ 201.6	$ (60.0)
Net Gains/(Losses) Recognized in Operating Income (in millions)	(2.4)	(8.6)	(8.4)
Operating expense
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)	3.7	(5.5)	(0.8)
Net Gains/(Losses) Recognized in Operating Income (in millions)	$ 0.0	$ 0.0	$ 0.0

Collaborative and Other Relationships - Co-promotion Profit Sharing Formula (Details) - RITUXAN	Dec. 31, 2023
Collaborative arrangements and non-collaborative arrangement transactions
After LUNSUMIO Approval until the First Threshold Date	37.50%
After First Threshold Date until the Second Threshold Date	35.00%
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Four	30.00%

Intangible Assets and Goodwill (Tables)

12 Months Ended

Dec. 31, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets

Intangible assets, net of accumulated amortization, impairment charges and adjustments are summarized as follows:


		As of December 31, 2023						As of December 31, 2022
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology
Acquired and in-licensed rights and patents	2-22 years	$	8,180.2	$	(2,440.7)	$	5,739.5	$	3,866.6	$	(2,219.1)	$	1,647.5
Developed technology and other	13-31 years	3,548.6		(3,429.1)		119.5		3,548.7		(3,410.1)		138.6

Total completed technology		11,728.8		(5,869.8)		5,859.0		7,415.3		(5,629.2)		1,786.1
In-process research and development	Indefinite until commercialization	2,340.0		—		2,340.0		—		—		—
Priority review voucher	Indefinite	100.0		—		100.0		—		—		—
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	14,232.8	$	(5,869.8)	$	8,363.0	$	7,479.3	$	(5,629.2)	$	1,850.1

Estimated future amortization of intangible assets

The estimated future amortization of finite-lived intangible assets for the next five years is expected to be as follows:


(In millions)	As of December 31, 2023
2024	$	345.0
2025	470.0
2026	485.0
2027	480.0
2028	495.0

Summary of roll forward of the changes in goodwill

The following table provides a roll forward of the changes in our goodwill balance:


	As of December 31,
(In millions)	2023		2022
Goodwill, beginning of year	$	5,749.0	$	5,761.1
Goodwill resulting from Reata acquisition	464.5		—

Other	5.7		(12.1)
Goodwill, end of year	$	6,219.2	$	5,749.0

- Definition

Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Acquisitions - Purchase Price Consideration (Details) - Reata Pharmaceuticals, Inc $ / shares in Units, shares in Thousands, $ in Millions	Sep. 26, 2023 USD ($) $ / shares shares
Business Acquisition [Line Items]
Total transaction value	$ 6,602.9
Fair value of Reata equity compensation pre-acquisition services and related taxes	590.5
Consideration transferred	$ 7,193.4
Price per share \| $ / shares	$ 172.50
Number of common stock shares acquired \| shares	38,300

Collaborative and Other Relationships - Acorda (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Acorda
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	$ 55.2	$ 46.1	$ 46.6

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Mar. 31, 2023	Dec. 31, 2020
Tax Credit Carryforward [Line Items]
Income taxes paid	$ 185.4
Deferred tax liabilities, temporary differences, purchase accounting, foreign subsidiaries	1,500.0
Total deferred charges and prepaid taxes	69.3	$ 56.6
Deferred tax asset, net		100.0
Valuation allowance	1,278.7	2,003.3		$ 85.0
Unrecognized Tax Benefits	173.4	606.4	$ 563.4		$ 75.7
Unrecognized tax benefit	147.6	134.0	87.5
Net interest expense	5.1	0.7	2.7
Unrecognized tax benefits, interest on income taxes accrued	30.2	25.2
Decrease in unrecognized tax benefits is reasonably possible	20.0
Neurimmune
Tax Credit Carryforward [Line Items]
Effective income tax rate reconciliation, disposition of business, amount	7.4	85.0	390.0
2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax liabilities	419.5	558.0
State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	21.0
Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Valuation allowance	1,278.7	2,003.3	1,961.3		$ 1,753.9
Increase in unrecognized tax benefit	(450.0)		$ 455.0
Unrecognized Tax Benefits		$ 450.0
Foreign Tax Authority \| Neurimmune
Tax Credit Carryforward [Line Items]
Valuation allowance increase (decrease)	(470.3)
Foreign Tax Authority \| Neurimmune \| Swiss Federal Tax Administration (FTA)
Tax Credit Carryforward [Line Items]
Valuation allowance increase (decrease)	(230.3)
General Business \| Domestic Country
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount	141.8
Operating loss carryforwards	913.1
General Business \| Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount	13,000.0
Operating loss carryforwards	12,200.0
Research \| State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount	140.5
Minimum
Tax Credit Carryforward [Line Items]
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting	300.0
Maximum
Tax Credit Carryforward [Line Items]
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting	$ 400.0

Financial Instruments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023
Business Acquisition [Line Items]
Average maturity of marketable securities, months	8 months
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio	$ 846.0	$ 460.7

Revenue - Revenues by Product (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total product revenue	$ 9,835.6	$ 10,173.4	$ 10,981.7
TECFIDERA
Disaggregation of Revenue [Line Items]
Total product revenue	1,012.5	1,443.9	1,951.9
VUMERITY
Disaggregation of Revenue [Line Items]
Total product revenue	576.3	553.4	410.4
Total Fumarate
Disaggregation of Revenue [Line Items]
Total product revenue	1,588.8	1,997.3	2,362.3
AVONEX
Disaggregation of Revenue [Line Items]
Total product revenue	811.0	973.5	1,208.7
PLEGRIDY
Disaggregation of Revenue [Line Items]
Total product revenue	294.7	331.9	357.4
Total Interferon
Disaggregation of Revenue [Line Items]
Total product revenue	1,105.7	1,305.4	1,566.1
TYSABRI
Disaggregation of Revenue [Line Items]
Total product revenue	1,876.9	2,030.9	2,063.1
FAMPYRA
Disaggregation of Revenue [Line Items]
Total product revenue	90.5	96.6	105.2
Subtotal: Multiple Sclerosis
Disaggregation of Revenue [Line Items]
Total product revenue	4,661.9	5,430.2	6,096.7
SPINRAZA
Disaggregation of Revenue [Line Items]
Total product revenue	1,741.2	1,793.5	1,905.1
QALSODY
Disaggregation of Revenue [Line Items]
Total product revenue	5.9	0.0	0.0
SKYCLARYS
Disaggregation of Revenue [Line Items]
Total product revenue	55.9	0.0	0.0
Subtotal: Rare Disease
Disaggregation of Revenue [Line Items]
Total product revenue	1,803.0	1,793.5	1,905.1
BENEPALI
Disaggregation of Revenue [Line Items]
Total product revenue	438.8	441.0	498.3
IMRALDI
Disaggregation of Revenue [Line Items]
Total product revenue	222.1	224.5	233.4
FLIXABI
Disaggregation of Revenue [Line Items]
Total product revenue	77.4	81.3	99.4
BYOOVIZ
Disaggregation of Revenue [Line Items]
Total product revenue	31.7	4.3	0.0
Subtotal: Biosimilars
Disaggregation of Revenue [Line Items]
Total product revenue	770.0	751.1	831.1
Other
Disaggregation of Revenue [Line Items]
Total product revenue	11.8	13.0	14.0
Total product revenue
Disaggregation of Revenue [Line Items]
Total product revenue	7,246.7	7,987.8	8,846.9
United States \| TECFIDERA
Disaggregation of Revenue [Line Items]
Total product revenue	263.1	417.7	680.6
United States \| VUMERITY
Disaggregation of Revenue [Line Items]
Total product revenue	512.1	521.3	408.9
United States \| Total Fumarate
Disaggregation of Revenue [Line Items]
Total product revenue	775.2	939.0	1,089.5
United States \| AVONEX
Disaggregation of Revenue [Line Items]
Total product revenue	536.7	649.2	830.2
United States \| PLEGRIDY
Disaggregation of Revenue [Line Items]
Total product revenue	126.2	148.4	152.9
United States \| Total Interferon
Disaggregation of Revenue [Line Items]
Total product revenue	662.9	797.6	983.1
United States \| TYSABRI
Disaggregation of Revenue [Line Items]
Total product revenue	997.9	1,123.4	1,142.2
United States \| FAMPYRA
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| Subtotal: Multiple Sclerosis
Disaggregation of Revenue [Line Items]
Total product revenue	2,436.0	2,860.0	3,214.8
United States \| SPINRAZA
Disaggregation of Revenue [Line Items]
Total product revenue	610.5	600.2	587.9
United States \| QALSODY
Disaggregation of Revenue [Line Items]
Total product revenue	5.8	0.0	0.0
United States \| SKYCLARYS
Disaggregation of Revenue [Line Items]
Total product revenue	55.9	0.0	0.0
United States \| Subtotal: Rare Disease
Disaggregation of Revenue [Line Items]
Total product revenue	672.2	600.2	587.9
United States \| BENEPALI
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| IMRALDI
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| FLIXABI
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| BYOOVIZ
Disaggregation of Revenue [Line Items]
Total product revenue	29.2	4.3	0.0
United States \| Subtotal: Biosimilars
Disaggregation of Revenue [Line Items]
Total product revenue	29.2	4.3	0.0
United States \| Other
Disaggregation of Revenue [Line Items]
Total product revenue	4.0	4.8	3.0
United States \| Total product revenue
Disaggregation of Revenue [Line Items]
Total product revenue	3,141.4	3,469.3	3,805.7
Rest of World \| TECFIDERA
Disaggregation of Revenue [Line Items]
Total product revenue	749.4	1,026.2	1,271.3
Rest of World \| VUMERITY
Disaggregation of Revenue [Line Items]
Total product revenue	64.2	32.1	1.5
Rest of World \| Total Fumarate
Disaggregation of Revenue [Line Items]
Total product revenue	813.6	1,058.3	1,272.8
Rest of World \| AVONEX
Disaggregation of Revenue [Line Items]
Total product revenue	274.3	324.3	378.5
Rest of World \| PLEGRIDY
Disaggregation of Revenue [Line Items]
Total product revenue	168.5	183.5	204.5
Rest of World \| Total Interferon
Disaggregation of Revenue [Line Items]
Total product revenue	442.8	507.8	583.0
Rest of World \| TYSABRI
Disaggregation of Revenue [Line Items]
Total product revenue	879.0	907.5	920.9
Rest of World \| FAMPYRA
Disaggregation of Revenue [Line Items]
Total product revenue	90.5	96.6	105.2
Rest of World \| Subtotal: Multiple Sclerosis
Disaggregation of Revenue [Line Items]
Total product revenue	2,225.9	2,570.2	2,881.9
Rest of World \| SPINRAZA
Disaggregation of Revenue [Line Items]
Total product revenue	1,130.7	1,193.3	1,317.2
Rest of World \| QALSODY
Disaggregation of Revenue [Line Items]
Total product revenue	0.1	0.0	0.0
Rest of World \| SKYCLARYS
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
Rest of World \| Subtotal: Rare Disease
Disaggregation of Revenue [Line Items]
Total product revenue	1,130.8	1,193.3	1,317.2
Rest of World \| BENEPALI
Disaggregation of Revenue [Line Items]
Total product revenue	438.8	441.0	498.3
Rest of World \| IMRALDI
Disaggregation of Revenue [Line Items]
Total product revenue	222.1	224.5	233.4
Rest of World \| FLIXABI
Disaggregation of Revenue [Line Items]
Total product revenue	77.4	81.3	99.4
Rest of World \| BYOOVIZ
Disaggregation of Revenue [Line Items]
Total product revenue	2.5	0.0	0.0
Rest of World \| Subtotal: Biosimilars
Disaggregation of Revenue [Line Items]
Total product revenue	740.8	746.8	831.1
Rest of World \| Other
Disaggregation of Revenue [Line Items]
Total product revenue	7.8	8.2	11.0
Rest of World \| Total product revenue
Disaggregation of Revenue [Line Items]
Total product revenue	$ 4,105.3	$ 4,518.5	$ 5,041.2

Inventory (Tables)

12 Months Ended

Dec. 31, 2023

Inventory Disclosure [Abstract]

Components of inventory

The components of inventory are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Raw materials	$	426.9	$	413.2
Work in process	1,926.8		751.9
Finished goods	255.4		200.4
Total inventory	$	2,609.1	$	1,365.5

Balance Sheet Classification:
Inventory	$	2,527.4	$	1,344.4
Investments and other assets	81.7		21.1
Total inventory	$	2,609.1	$	1,365.5

We recorded approximately $1.3 billion of acquired inventory, which includes measurement period adjustments, related to SKYCLARYS as a result of our acquisition of Reata in September 2023. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

Collaborative and Other Relationships - Summary of Activity Related to the UCB Collaboration (Details) - Research and development - UCB Pharma S.A. - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 60.7	$ 68.0	$ 84.2
Expense reflected within statements of income	$ 30.3	$ 34.0	$ 42.1

Share-Based Payments - Assumptions Used in Valuation of Performance Shares (Details) - Performance stock units settled in cash - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award
Expected dividend yield	0.00%	0.00%
Minimum range of risk-free interest rates	4.10%	1.80%
Maximum range of risk-free interest rates		3.90%
Average stock price on grant date minimum	$ 283.93	$ 231.31
Average stock price on grant date maximum		294.86
Granted (in dollars per share)	$ 383.61	$ 294.43
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Range of expected stock price volatility	44.70%	44.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Range of expected stock price volatility		45.90%

Segment Information - Geographic Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue, Major Customer [Line Items]
Revenue	$ 9,835.6	$ 10,173.4	$ 10,981.7
Long-lived assets	3,729.7	3,702.5	3,791.8
U.S.
Revenue, Major Customer [Line Items]
Long-lived assets	1,443.0	1,369.4	1,390.5
Europe
Revenue, Major Customer [Line Items]
Long-lived assets	2,248.0	2,275.8	2,337.8
Germany
Revenue, Major Customer [Line Items]
Long-lived assets	17.5	21.0	25.4
Asia
Revenue, Major Customer [Line Items]
Long-lived assets	8.3	13.7	16.4
Other
Revenue, Major Customer [Line Items]
Long-lived assets	12.9	22.6	21.7
Product revenue, net
Revenue, Major Customer [Line Items]
Revenue	7,246.7	7,987.8	8,846.9
Product revenue, net \| U.S.
Revenue, Major Customer [Line Items]
Revenue	3,141.4	3,469.3	3,805.7
Product revenue, net \| Europe
Revenue, Major Customer [Line Items]
Revenue	2,127.4	2,401.3	2,626.0
Product revenue, net \| Germany
Revenue, Major Customer [Line Items]
Revenue	868.0	926.2	1,162.4
Product revenue, net \| Asia
Revenue, Major Customer [Line Items]
Revenue	649.4	672.1	688.0
Product revenue, net \| Other
Revenue, Major Customer [Line Items]
Revenue	460.5	518.9	564.8
Revenue from anti-CD20 therapeutic programs
Revenue, Major Customer [Line Items]
Revenue	1,689.6	1,700.5	1,658.5
Revenue from anti-CD20 therapeutic programs \| U.S.
Revenue, Major Customer [Line Items]
Revenue	1,618.5	1,636.4	1,596.7
Revenue from anti-CD20 therapeutic programs \| Europe
Revenue, Major Customer [Line Items]
Revenue	0.4	0.1	0.0
Revenue from anti-CD20 therapeutic programs \| Germany
Revenue, Major Customer [Line Items]
Revenue	0.0	0.0	0.0
Revenue from anti-CD20 therapeutic programs \| Asia
Revenue, Major Customer [Line Items]
Revenue	0.0	0.0	0.0
Revenue from anti-CD20 therapeutic programs \| Other
Revenue, Major Customer [Line Items]
Revenue	70.7	64.0	61.8
Contract manufacturing, royalty and other revenue
Revenue, Major Customer [Line Items]
Revenue	899.3	485.1	476.3
Contract manufacturing, royalty and other revenue \| U.S.
Revenue, Major Customer [Line Items]
Revenue	673.6	425.8	429.9
Contract manufacturing, royalty and other revenue \| Europe
Revenue, Major Customer [Line Items]
Revenue	11.7	11.7	9.7
Contract manufacturing, royalty and other revenue \| Germany
Revenue, Major Customer [Line Items]
Revenue	0.0	0.0	0.0
Contract manufacturing, royalty and other revenue \| Asia
Revenue, Major Customer [Line Items]
Revenue	214.0	47.6	36.7
Contract manufacturing, royalty and other revenue \| Other
Revenue, Major Customer [Line Items]
Revenue	$ 0.0	$ 0.0	$ 0.0

Equity - Summary of Common Stock (Details) - shares shares in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Equity [Abstract]
Common stock authorized (in shares)	1,000.0	1,000.0	1,000.0
Common stock issued (in shares)	168.7	167.9	170.8
Common stock outstanding (in shares)	144.9	144.0	147.0

Collaborative and Other Relationships - Summary of Activity Related to Sage Therapeutics (Details) - Sage Therapeutics - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Research and development
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 176.7	$ 173.3	$ 167.7
Expense reflected within statements of income	88.3	86.7	83.8
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	187.0	109.9	36.4
Expense reflected within statements of income	$ 93.5	$ 55.0	$ 18.2

Income Taxes - Tax Rate (Details)	12 Months Ended
Income Taxes - Tax Rate (Details)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Statutory rate	21.00%	21.00%	21.00%
State taxes	1.10%	1.10%	0.80%
Taxes on foreign earnings	(5.90%)	(4.90%)	(10.50%)
Tax credits	(7.30%)	(1.70%)	(3.80%)
Purchased inventory valuation step-up and intangible assets	0.70%	0.30%	(1.60%)
GILTI	(0.60%)	0.70%	1.30%
Sale of Samsung Bioepis	0.00%	(1.60%)	0.00%
Litigation settlement agreement	0.00%	2.60%	0.00%
Neurimmune tax impacts	0.00%	2.30%	(5.30%)
Internal reorganization	(0.10%)	(1.40%)	0.00%
Other, including permanent items	1.50%	(0.80%)	1.10%
Effective tax rate	10.40%	17.60%	3.00%

Revenue - Reserves for Discounts and Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 1,035.0	$ 935.3	$ 1,276.0
Current provisions relating to sales in current year	3,474.7	3,394.4	3,700.6
Adjustments relating to prior years	(19.6)	(8.6)	(103.4)
Payments/credits relating to sales in current year	(2,519.8)	(2,576.8)	(2,882.8)
Payments/credits relating to sales in prior years	(908.3)	(709.3)	(1,055.1)
Ending balance	1,062.0	1,035.0	935.3
Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	153.8	137.7	141.4
Current provisions relating to sales in current year	735.6	666.6	736.7
Adjustments relating to prior years	(0.4)	(2.8)	(4.0)
Payments/credits relating to sales in current year	(572.9)	(514.9)	(599.3)
Payments/credits relating to sales in prior years	(142.8)	(132.8)	(137.1)
Ending balance	173.3	153.8	137.7
Contractual Adjustments
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	857.7	759.6	1,093.0
Current provisions relating to sales in current year	2,720.1	2,715.5	2,948.7
Adjustments relating to prior years	(38.4)	1.4	(96.1)
Payments/credits relating to sales in current year	(1,944.8)	(2,060.7)	(2,283.1)
Payments/credits relating to sales in prior years	(737.5)	(558.1)	(902.9)
Ending balance	857.1	857.7	759.6
Returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	23.5	38.0	41.6
Current provisions relating to sales in current year	19.0	12.3	15.2
Adjustments relating to prior years	19.2	(7.2)	(3.3)
Payments/credits relating to sales in current year	(2.1)	(1.2)	(0.4)
Payments/credits relating to sales in prior years	(28.0)	(18.4)	(15.1)
Ending balance	$ 31.6	$ 23.5	$ 38.0

Share-Based Payments - Assumptions Used in Valuation of Market Based Stock Units (Details) - Market stock units - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award
Expected dividend yield		0.00%
Minimum range of risk-free interest rates		0.06%
Maximum range of risk-free interest rates		0.21%
Average stock price on grant date minimum		$ 262.23
Average stock price on grant date maximum		360.31
Granted (in dollars per share)	$ 0	$ 358.77
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Range of expected stock price volatility		54.80%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Range of expected stock price volatility		61.60%

Revenue

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Abstract]

Revenue


Note 5:			Revenue

Product Revenue

Revenue by product are summarized as follows:


	For the Years Ended December 31,
	2023						2022						2021
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	263.1	$	749.4	$	1,012.5	$	417.7	$	1,026.2	$	1,443.9	$	680.6	$	1,271.3	$	1,951.9
VUMERITY	512.1		64.2		576.3		521.3		32.1		553.4		408.9		1.5		410.4
Total Fumarate	775.2		813.6		1,588.8		939.0		1,058.3		1,997.3		1,089.5		1,272.8		2,362.3
AVONEX	536.7		274.3		811.0		649.2		324.3		973.5		830.2		378.5		1,208.7
PLEGRIDY	126.2		168.5		294.7		148.4		183.5		331.9		152.9		204.5		357.4
Total Interferon	662.9		442.8		1,105.7		797.6		507.8		1,305.4		983.1		583.0		1,566.1
TYSABRI	997.9		879.0		1,876.9		1,123.4		907.5		2,030.9		1,142.2		920.9		2,063.1
FAMPYRA	—		90.5		90.5		—		96.6		96.6		—		105.2		105.2
Subtotal: Multiple Sclerosis	2,436.0		2,225.9		4,661.9		2,860.0		2,570.2		5,430.2		3,214.8		2,881.9		6,096.7

Rare Disease:
SPINRAZA	610.5		1,130.7		1,741.2		600.2		1,193.3		1,793.5		587.9		1,317.2		1,905.1
QALSODY(1)	5.8		0.1		5.9		—		—		—		—		—		—
SKYCLARYS(2)	55.9		—		55.9		—		—		—		—		—		—
Subtotal: Rare Disease	672.2		1,130.8		1,803.0		600.2		1,193.3		1,793.5		587.9		1,317.2		1,905.1

Biosimilars:
BENEPALI	—		438.8		438.8		—		441.0		441.0		—		498.3		498.3
IMRALDI	—		222.1		222.1		—		224.5		224.5		—		233.4		233.4
FLIXABI	—		77.4		77.4		—		81.3		81.3		—		99.4		99.4
BYOOVIZ(3)	29.2		2.5		31.7		4.3		—		4.3		—		—		—
Subtotal: Biosimilars	29.2		740.8		770.0		4.3		746.8		751.1		—		831.1		831.1

Other(4)	4.0		7.8		11.8		4.8		8.2		13.0		3.0		11.0		14.0
Total product revenue	$	3,141.4	$	4,105.3	$	7,246.7	$	3,469.3	$	4,518.5	$	7,987.8	$	3,805.7	$	5,041.2	$	8,846.9

(1) QALSODY became commercially available in the U.S. during the second quarter of 2023.

(2) SKYCLARYS was obtained as part of our acquisition of Reata in September 2023. SKYCLARYS became commercially available in the U.S. during the second quarter of 2023 and we began recognizing revenue from SKYCLARYS in the U.S. during the fourth quarter of 2023, subsequent to our acquisition.

(3) BYOOVIZ became commercially available in the U.S. during the third quarter of 2022 and commercially available in certain international markets in 2023.

(4) Other includes FUMADERM, ADUHELM and ZURZUVAE, which became commercially available in the U.S. during the fourth quarter of 2023.

We recognized revenue from two wholesalers accounting for 27.0% and 9.9% of gross product revenue in 2023, 26.8% and 11.1% of gross product revenue in 2022 and 28.8% and 10.1% of gross product revenue in 2021, respectively.

As of December 31, 2023, two wholesale distributors individually accounted for approximately 24.6% and 11.6% of net accounts receivable associated with our product sales, as compared to 22.7% and 10.9% as of December 31, 2022, respectively.

An analysis of the change in reserves for discounts and allowances is summarized as follows:


	December 31, 2023
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	153.8	$	857.7	$	23.5	$	1,035.0
Current provisions relating to sales in current year	735.6		2,720.1		19.0		3,474.7
Adjustments relating to prior years	(0.4)		(38.4)		19.2		(19.6)
Payments/credits relating to sales in current year	(572.9)		(1,944.8)		(2.1)		(2,519.8)
Payments/credits relating to sales in prior years	(142.8)		(737.5)		(28.0)		(908.3)
Ending balance	$	173.3	$	857.1	$	31.6	$	1,062.0


	December 31, 2022
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	137.7	$	759.6	$	38.0	$	935.3
Current provisions relating to sales in current year	666.6		2,715.5		12.3		3,394.4
Adjustments relating to prior years	(2.8)		1.4		(7.2)		(8.6)
Payments/credits relating to sales in current year	(514.9)		(2,060.7)		(1.2)		(2,576.8)
Payments/credits relating to sales in prior years	(132.8)		(558.1)		(18.4)		(709.3)
Ending balance	$	153.8	$	857.7	$	23.5	$	1,035.0


	December 31, 2021
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	141.4	$	1,093.0	$	41.6	$	1,276.0
Current provisions relating to sales in current year	736.7		2,948.7		15.2		3,700.6
Adjustments relating to prior years	(4.0)		(96.1)		(3.3)		(103.4)
Payments/credits relating to sales in current year	(599.3)		(2,283.1)		(0.4)		(2,882.8)
Payments/credits relating to sales in prior years	(137.1)		(902.9)		(15.1)		(1,055.1)
Ending balance	$	137.7	$	759.6	$	38.0	$	935.3

The total reserves above, which are included in our consolidated balance sheets, are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Reduction of accounts receivable	$	135.5	$	143.4
Component of accrued expense and other	926.5		891.6
Total revenue-related reserves	$	1,062.0	$	1,035.0

Revenue from Anti-CD20 Therapeutic Programs

Revenue from anti-CD20 therapeutic programs is summarized in the table below. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Royalty revenue on sales of OCREVUS	$	1,266.2	$	1,136.3	$	991.7
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4		547.0		647.7
Other revenue from anti-CD20 therapeutic programs	14.0		17.2		19.1
Total revenue from anti-CD20 therapeutic programs	$	1,689.6	$	1,700.5	$	1,658.5

(1) LUNSUMIO became commercially available in the U.S. during the first quarter of 2023.

Approximately 17.2%, 16.7% and 15.1% of our total revenue in 2023, 2022 and 2021, respectively, was derived from our collaboration arrangements with Genentech. For additional information on our collaboration arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Contract Manufacturing, Royalty and Other Revenue

Contract manufacturing, royalty and other revenue is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021




Contract manufacturing revenue	$	848.2	$	417.7	$	427.7
Royalty and other revenue	51.1		67.4		48.6
Total contract manufacturing, royalty and other revenue	$	899.3	$	485.1	$	476.3

Contract Manufacturing Revenue

Contract manufacturing revenue primarily reflects amounts earned under contract manufacturing agreements with our strategic customers. During the first quarter of 2023 we began recognizing contract manufacturing revenue for LEQEMBI, upon accelerated approval of LEQEMBI in the U.S. Prior to accelerated approval, our share of contract manufacturing amounts related to LEQEMBI were recognized in research and development expense within our consolidated statements of income.

During the third quarter of 2019, we amended our agreement with a contract manufacturing customer pursuant to which we licensed certain of our manufacturing-related intellectual property to the customer. In the second quarter of 2020, the customer received regulatory approval for its product that is being manufactured using certain of our manufacturing-related intellectual property. As a result we were entitled to $500.0 million in a series of three payments. The first payment became due upon a regulatory approval of such product and was received during the second quarter of 2020. The second payment became due upon the first anniversary of the regulatory approval and was received during the second quarter of 2021. The third payment became due upon the second anniversary of the regulatory approval and was received during the second quarter of 2022.

Royalty and Other Revenue

For additional information on our collaboration arrangements with Eisai and our license arrangements with Samsung Bioepis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-9

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-10

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-15

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
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-Paragraph 12
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-12

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-13

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Topic 606
-Publisher FASB
-URI https://asc.fasb.org//606/tableOfContent

+ Details

Intangible Assets and Goodwill - Summary of Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets, Net [Abstract]
Finite-Lived Intangible Assets, Gross	$ 11,728.8	$ 7,415.3
Accumulated Amortization	(5,869.8)	(5,629.2)
Net	5,859.0	1,786.1
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Cost	14,232.8	7,479.3
Accumulated Amortization	5,869.8	5,629.2
Net	8,363.0	1,850.1
In-process research and development
Indefinite-Lived Intangible Assets [Line Items]
Cost and net	2,340.0	0.0
Priority review voucher
Indefinite-Lived Intangible Assets [Line Items]
Cost and net	100.0	0.0
Trademarks and trade names
Indefinite-Lived Intangible Assets [Line Items]
Cost and net	64.0	64.0
Acquired and in-licensed rights and patents
Finite-Lived Intangible Assets, Net [Abstract]
Finite-Lived Intangible Assets, Gross	8,180.2	3,866.6
Accumulated Amortization	(2,440.7)	(2,219.1)
Net	5,739.5	1,647.5
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Accumulated Amortization	$ 2,440.7	2,219.1
Acquired and in-licensed rights and patents \| Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated life (in years)	2 years
Acquired and in-licensed rights and patents \| Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated life (in years)	22 years
Developed technology and other
Finite-Lived Intangible Assets, Net [Abstract]
Finite-Lived Intangible Assets, Gross	$ 3,548.6	3,548.7
Accumulated Amortization	(3,429.1)	(3,410.1)
Net	119.5	138.6
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Accumulated Amortization	$ 3,429.1	$ 3,410.1
Developed technology and other \| Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated life (in years)	13 years
Developed technology and other \| Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated life (in years)	31 years

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements


Note 8:			Fair Value Measurements

The tables below present information about our assets and liabilities that are regularly measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques we utilized to determine such fair value:


	As of December 31, 2023
(In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	610.7	$	—	$	610.7	$	—




Marketable equity securities	416.8		416.8		—		—
Other current assets:
Receivable from Samsung BioLogics(1)	430.0		—		—		430.0
Derivative contracts	11.9		—		11.9		—
Other non-current assets:
Plan assets for deferred compensation	37.5		—		37.5		—

Total	$	1,506.9	$	416.8	$	660.1	$	430.0
Liabilities:
Derivative contracts	$	31.6	$	—	$	31.6	$	—

Total	$	31.6	$	—	$	31.6	$	—

(1) Represents the fair value of the current payment due from Samsung BioLogics as a result of the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics during the second quarter of 2022, for which we elected the fair value option. For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

During the third quarter of 2023 we sold all of our marketable debt securities and used the proceeds to partially fund our acquisition of Reata. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.


	As of December 31, 2022
(In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	2,847.6	$	—	$	2,847.6	$	—
Marketable debt securities:
Corporate debt securities	1,231.6		—		1,231.6		—
Government securities	810.3		—		810.3		—
Mortgage and other asset backed securities	137.3		—		137.3		—
Marketable equity securities	791.1		791.1		—		—
Other current assets:
Receivable from Samsung BioLogics(1)	798.8		—		—		798.8
Other non-current assets:
Derivative contracts	63.0		—		63.0		—
Plan assets for deferred compensation	32.8		—		32.8		—
Receivable from Samsung BioLogics(1)	405.4		—		—		405.4
Total	$	7,117.9	$	791.1	$	5,122.6	$	1,204.2
Liabilities:
Derivative contracts	$	26.0	$	—	$	26.0	$	—

Total	$	26.0	$	—	$	26.0	$	—

(1) Represents the fair value of the current and non-current payments due from Samsung BioLogics as a result of the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics during the second quarter of 2022, for which we elected the fair value option. For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

Our marketable equity securities represent investments in publicly traded equity securities. Our ability to liquidate our investments in Denali, Sage and Sangamo may be limited by the size of our interest, the volume of market related activity, our concentrated level of ownership and potential restrictions resulting from our status as a collaborator. Therefore, we may realize significantly less than the current value of such investments.

For additional information on our investments in Denali, Sangamo and Sage common stock, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

There have been no material impairments of our assets measured and carried at fair value as of December 31, 2023 and 2022. In addition, there have been no changes in valuation techniques as of December 31, 2023 and 2022.

For a description of our validation procedures related to prices provided by third-party pricing services and our option pricing valuation model, please read the Fair Value Measurements section within Note 1, Summary of Significant Accounting Policies, to these consolidated financial statements.

Level 3 Assets and Liabilities Held at Fair Value

There were no transfers of assets or liabilities into or out of Level 3 as of December 31, 2023 and 2022.

Contingent Consideration Obligations

In connection with our acquisition of Convergence, we agreed to make additional payments based upon the achievement of certain milestone events. The following table provides a roll forward of the fair value of our contingent consideration obligations, which were classified as Level 3 measurements:


	As of December 31,
(In millions)	2022
Fair value, beginning of year	$	209.1
Changes in fair value	(209.1)

Fair value, end of year	$	—

For the year ended December 31, 2022, the changes in fair value of our contingent consideration obligations were primarily due to the discontinuation of further development efforts related to vixotrigine for the potential treatment of TGN and DPN, resulting in a reduction of our contingent consideration obligations of approximately $195.4 million, reducing the remaining fair value of vixotrigine to zero, as well as changes in the interest rates used to revalue our contingent consideration liabilities.

Changes in the fair values of our contingent consideration obligations are recorded in (gain) loss on fair value remeasurement of contingent consideration in our consolidated statements of income. The fair values of the contingent consideration liabilities were based on a probability-adjusted discounted cash flow calculation using Level 3 fair value measurements and inputs. For additional information on the valuation techniques and inputs utilized in the valuation of our financial assets and liabilities, please read Note 1, Summary of Significant Accounting Policies, to these consolidated financial statements.

Convergence Pharmaceuticals Holdings Limited

In connection with our acquisition of Convergence in February 2015 we recorded a contingent consideration obligation of $274.5 million. As of December 31, 2021, the fair value of this contingent consideration obligation was $209.1 million. During the fourth quarter of 2022 we discontinued further development of vixotrigine based on regulatory, development and commercialization challenges. As a result, the fair value of the contingent consideration obligations related to Convergence has been adjusted to zero, resulting in a pre-tax gain of approximately $209.1 million for the year ended December 31, 2022. This pre-tax gain was recorded in (gain) loss on fair value remeasurement of contingent consideration within our consolidated statements of income.

Nonrecurring Fair Value Measurements

For the year ended December 31, 2022, we recorded impairment charges of $119.6 million related to vixotrigine. As a result, the remaining book values associated with these programs were reduced to zero. For the year ended December 31, 2021, we recorded impairment charges of $365.0 million related to BIIB111 and $220.0 million related to BIIB112. As a result, the remaining book values associated with these programs were reduced to zero.

For additional information on our impairments for intangible assets, please read Note 7, Intangible Assets and Goodwill, to these consolidated financial statements.

Financial Instruments Not Carried at Fair Value

Other Financial Instruments

Due to the short-term nature of certain financial instruments, the carrying value reflected in our consolidated balance sheets for current accounts receivable, due from anti-CD20 therapeutic programs, other current assets, accounts payable and accrued expense and other, approximates fair value.

Debt Instruments

The fair values of our debt instruments, which are Level 2 liabilities, are summarized as follows:


	Fair Value As of December 31,
(In millions)	2023		2022
Current portion:
2023 Term Loan 364-day tranche(1)	$	150.0	$	—
Current portion of notes payable and term loan	150.0		—

Non-current portion:
2023 Term Loan three-year tranche(1)	500.0		—
4.050% Senior Notes due September 15, 2025	1,721.5		1,699.9
2.250% Senior Notes due May 1, 2030	1,279.3		1,219.0
5.200% Senior Notes due September 15, 2045	1,089.7		1,033.2
3.150% Senior Notes due May 1, 2050	1,049.0		989.0
3.250% Senior Notes due February 15, 2051	498.2		469.1
Non-current portion of notes payable and term loan	6,137.7		5,410.2
Total notes payable and term loan	$	6,287.7	$	5,410.2

(1) In connection with our acquisition of Reata we drew $1.0 billion from our 2023 Term Loan, comprised of a $500.0 million floating rate 364-day tranche and a $500.0 million floating rate three-year tranche. For additional information on our 2023 Term Loan, please read Note 13, Indebtedness, to these consolidated financial statements.

The fair values of each of our series of Senior Notes were determined through market, observable and corroborated sources. The changes in the fair values of our Senior Notes as of December 31, 2023, compared to 2022, are primarily related to increases in U.S. treasury yields partially offset by a decrease in credit spreads used to value our Senior Notes since December 31, 2022. For additional information related to our Senior Notes, please read Note 13, Indebtedness, to these consolidated financial statements.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Acquisitions

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Acquisitions


Note 2:			Acquisitions

Reata Pharmaceuticals, Inc.

On September 26, 2023, we completed the acquisition of all of the issued and outstanding shares of Reata, a biopharmaceutical company focused on developing therapeutics that regulate cellular metabolism and inflammation in serious neurologic diseases. As a result of this transaction we acquired SKYCLARYS (omaveloxolone), the first and only drug approved in the U.S. and the E.U. for the treatment of Friedreich's Ataxia in adults and adolescents aged 16 years and older, as well as other clinical and preclinical pipeline programs. The acquisition of Reata is expected to complement our global portfolio of neuromuscular and rare disease therapies. The addition of SKYCLARYS is anticipated to provide potential operating synergies with SPINRAZA and QALSODY.

Under the terms of this acquisition, we paid Reata shareholders $172.50 in cash for each issued and outstanding Reata share, which totaled approximately $6.6 billion. In addition, we agreed to pay approximately $983.9 million in cash for Reata's outstanding equity awards, inclusive of employer taxes, of which approximately $590.5 million was attributable to pre-acquisition services and is therefore reflected as a component of total purchase price paid. Of the $983.9 million paid to Reata's equity award holders, we recognized approximately $393.4 million as compensation attributable to the post-acquisition service period, of which $196.4 million was recognized as a charge to selling, general and administrative expense with the remaining $197.0 million as a charge to research and development expense within our consolidated statements of income for the year ended December 31, 2023. These amounts were associated with the accelerated vesting of stock options and RSUs previously granted to Reata employees that required no future services to vest.

We funded this acquisition through available cash, cash equivalents and marketable securities, supplemented by the issuance of a $1.0 billion term loan under our term loan credit agreement. For additional information on our term loan credit agreement, please read Note 13, Indebtedness, to these consolidated financial statements.

We accounted for this acquisition as a business combination using the acquisition method of accounting in accordance with ASC Topic 805, Business Combinations, and recorded assets acquired and liabilities assumed at their respective fair values as of the acquisition date.

Purchase Price Consideration

Total consideration transferred for the acquisition of Reata is summarized as follows:


(In millions)	As of September 26, 2023
Cash consideration paid to Reata shareholders(1)	$	6,602.9
Fair value of Reata equity compensation pre-acquisition services and related taxes(2)	590.5
Total consideration	$	7,193.4

(1) Represents cash consideration transferred of $172.50 per outstanding Reata ordinary share based on 38.3 million Reata shares outstanding at closing.

(2) Represents the fair value of Reata stock options and stock units issued to Reata equity award holders and the related taxes attributable to pre-acquisition vesting services.

Preliminary Purchase Price Allocation

The following table summarizes the provisional amounts recognized for assets acquired and liabilities assumed as of the acquisition date, as well as measurement period adjustments made year-to-date to the amounts initially recorded as of the acquisition date on September 26, 2023. The measurement period adjustments summarized below resulted from updates to our valuation assumptions related to the estimated amounts and timing of future cash flows associated with certain intangible assets, updates of our assumptions related to the quantities, selling location and remaining manufacturing and selling costs of acquired inventory, and other assets and liabilities. The related impact to our consolidated statements of income that would have been recognized in previous periods if the adjustments were recognized as of the acquisition date is immaterial.


(In millions)	Amounts Recognized as of Acquisition Date (as previously reported)		Measurement Period Adjustments		Amounts Recognized as of Acquisition Date (as adjusted)
Cash and cash equivalents	$	267.3	$	—	$	267.3
Accounts receivable	15.9		—		15.9
Inventory	1,692.0		(433.0)		1,259.0
Other current assets	53.6		—		53.6
Intangible assets:
Completed technology for SKYCLARYS (U.S.)	3,600.0		600.0		4,200.0
In-process research and development (omaveloxolone)	1,900.0		400.0		2,300.0
Priority review voucher	100.0		—		100.0
Other clinical programs	20.0		20.0		40.0
Operating lease assets	122.4		(1.2)		121.2
Accrued expense and other	(98.9)		(2.6)		(101.5)
Debt payable	(159.9)		—		(159.9)
Contingent payable to Blackstone(1)	(300.0)		—		(300.0)
Deferred tax liability	(922.5)		10.1		(912.4)
Operating lease liabilities	(151.8)		—		(151.8)
Other assets and liabilities, net	(2.0)		(0.5)		(2.5)
Total identifiable net assets	6,136.1		592.8		6,728.9
Goodwill	1,057.3		(592.8)		464.5
Total assets acquired and liabilities assumed	$	7,193.4	$	—	$	7,193.4

(1) For additional information on the contingent payable to Blackstone, please read Note 18, Other Consolidated Financial Statement Detail, to these consolidated financial statements.

Inventory: Total inventory acquired was approximately $1.3 billion, which reflects a step-up in the fair value of finished goods and work-in-process inventory for SKYCLARYS. The fair value was determined based on the estimated selling price of the inventory, less the remaining manufacturing and selling costs and a normal profit margin on those manufacturing and selling efforts. This fair value step-up adjustment will be amortized to cost of sales within our consolidated statements of income when the inventory is sold, which is expected to be within approximately 3 years from the acquisition date. For the year ended December 31, 2023, amortization from the fair value step-up adjustment as a result of inventory sold during the fourth quarter was approximately $31.5 million.

Intangible assets: Intangible assets are comprised of $4.2 billion related to SKYCLARYS commercialization rights in the U.S., $2.3 billion of IPR&D related to the omaveloxolone program outside the U.S., which had not yet received regulatory approval in the E.U. as of the acquisition date, $100.0 million related to a rare pediatric disease priority voucher which may be used to obtain priority review by the FDA for a future regulatory submission or sold to a third party and $40.0 million related to other clinical programs. The estimated fair values of the program related intangible assets were determined using a multi-period excess earnings method, a form of the income approach, utilizing a discount rate of 14.3% and the estimated fair value of the priority review voucher was based on recent external purchase and sale transactions of similar vouchers.

Our valuation of the SKYCLARYS commercialization rights reflects the assumption that, using an economic consumption model, the related $4.2 billion intangible asset will be amortized over its expected economic life. Our valuation of the $2.3 billion IPR&D asset relates to omaveloxolone, which was submitted to the EMA in 2023 and subsequently approved in the E.U. in February 2024. We expect sales to commence in certain countries in Europe during 2024, at which time we will begin amortizing the intangible asset over its expected economic life.

These fair value measurements were based on significant inputs not observable in the market and thus represent Level 3 fair value measurements.

Leases: We assumed responsibility for a single-tenant, build-to-suit building of approximately 327,400 square feet of office and laboratory space located in Plano, Texas, with an initial lease term of 16 years. We recorded a lease liability of approximately $151.8 million, which represents the net present value of rental expense over the remaining lease term of approximately 15 years, with a corresponding right-of-use asset of approximately $121.2 million, which represents our estimate of the fair value for a market participant of the current rental market in the Dallas, Texas area. Included in our estimate of the market rental rate is the value of any leasehold improvements or tenant allowances related to the building. We do not intend to occupy this building and are evaluating opportunities to sublease the property.

Goodwill: Goodwill was calculated as the excess of the consideration transferred over the net assets recognized and represents the future economic benefits arising from the other assets acquired that could not be individually identified and separately recognized. We recognized goodwill of approximately $464.5 million, which is not deductible for tax purposes. The goodwill recognized from our acquisition of Reata is primarily the result of the deferred tax consequences from the transaction recorded for financial statement purposes.

Acquisition-related expenses: Acquisition-related expenses, which were comprised primarily of regulatory, advisory and legal fees, and other transaction costs, totaled approximately $28.4 million and are included within selling, general and administrative expense within our consolidated statements of income for the year ended December 31, 2023.

Assumptions in the Allocations of Purchase Price

The results of operations of Reata, along with the estimated fair values of the assets acquired and liabilities assumed in the Reata acquisition, have been included in our consolidated financial statements since the closing of the Reata acquisition on September 26, 2023.

Our preliminary estimate of the fair value of the specifically identifiable assets acquired and liabilities assumed as of the date of acquisition is subject to the finalization of management's analysis related to certain matters, such as finalizing our assessment of income taxes. The final determination of these fair values will be completed as additional information becomes available but no later than one year from the acquisition date. The final determination may result in asset and liability fair values that are different than the preliminary estimates.

Subsequent to the acquisition date, our results of operations include the results of operations of Reata. Due to the immateriality of Reata's revenue and expense, additional pro forma information combining the results of operations of Biogen and Reata have not been included.

Earnings per Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Earnings per Share


Note 15:			Earnings per Share

Basic and diluted shares outstanding used in our earnings per share calculation are calculated as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Numerator:
Net income attributable to Biogen Inc.	$	1,161.1	$	3,046.9	$	1,556.1
Denominator:
Weighted average number of common shares outstanding	144.7		145.3		149.1
Effect of dilutive securities:

Time-vested restricted stock units	0.7		0.5		0.3
Market stock units	—		0.1		0.1
Performance stock units settled in stock	0.2		0.1		0.1
Dilutive potential common shares	0.9		0.7		0.5
Shares used in calculating diluted earnings per share	145.6		146.0		149.6

Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.

Earnings per share for the years ended December 31, 2022 and 2021, reflects the repurchase of approximately 3.6 million shares and 6.0 million shares of our common stock, respectively, under our share repurchase programs. There were no share repurchases of our common stock during the year ended December 31, 2023. For additional information on our share repurchase programs, please read Note 14, Equity, to these consolidated financial statements.

Collaborative and Other Relationships - Samsung Bioepis (Details) ₩ in Millions, $ in Millions	1 Months Ended						3 Months Ended	12 Months Ended
	Apr. 30, 2022 USD ($)	Dec. 31, 2019	Nov. 30, 2018 USD ($)	Nov. 30, 2018 KRW (₩)	Dec. 31, 2013	Feb. 29, 2012 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2023 USD ($) payment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 product	Mar. 31, 2022 KRW (₩)	Jun. 30, 2018	Feb. 29, 2012 KRW (₩)
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments								$ 0.0	$ 2.6	$ 34.9
Income tax (benefit) expense								135.3	632.8	52.5
Number of ophthalmolgy biosimilar products \| product											2
Collaboration profit sharing/(loss reimbursement)								218.8	(7.4)	7.2
Revenue								$ 9,835.6	10,173.4	10,981.7
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Investment in Samsung Bioepis \| ₩												₩ 581.6
Proceeds from divestiture of interest in joint venture	$ 1,000.0
Due from joint venture	1,300.0
Number of payments \| payment								2
Additional milestone payment	50.0
Expected profit share percentage		45.00%						50.00%
Accrued milestone payment							$ 15.0
Estimated additional payments upon achievement of development and commercial milestones								$ 180.0
Term of collaboration agreement					10 years
Term of collaboration agreement, additional length					5 years
Option exercise fee								60.0
Collaboration profit sharing/(loss reimbursement)								223.5	217.4	285.4
Revenue								13.6	20.6	20.7
Amounts receivable								9.9	2.0
Amounts payable								$ 73.7	40.5
Samsung Bioepis \| Payment Due At First Anniversary
Collaborative arrangements and non-collaborative arrangement transactions
Due from joint venture	812.5
Samsung Bioepis \| Payment Due At Second Anniversary
Collaborative arrangements and non-collaborative arrangement transactions
Due from joint venture	437.5
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Contributions by third party						$ 250.0								₩ 280,500.0
Joint venture ownership percentage						85.00%
Investment in Samsung Bioepis						$ 45.0								₩ 49,500.0
Ownership percentage						15.00%						49.90%		15.00%
Ownership percentage before additional purchase transaction													5.00%
Payments to increase investment in Samsung Bioepis			$ 676.6	₩ 759,500.0
Amount sold	2,300.0
Total basis difference	$ 675.0
Net profits on investment									2.6	34.9
Income (loss) from equity method investments									17.0	64.6
Amortization									14.4	$ 29.7
Income tax (benefit) expense									$ 31.2
Samsung Bioepis \| Inventories
Collaborative arrangements and non-collaborative arrangement transactions
Equity method investment basis difference amortization period	1 year 6 months
Samsung Bioepis \| Developed technology and other
Collaborative arrangements and non-collaborative arrangement transactions
Equity method investment basis difference amortization period	15 years

Derivative Instruments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Mar. 31, 2022	Jun. 30, 2018	Feb. 29, 2012
Derivatives, Fair Value [Line Items]
Range of durations of foreign currency forward contracts	12 months
Net gains (losses) of other income (expense) related to foreign currency forward contracts	$ 3.8	$ (34.7)	$ (43.3)
Samsung Bioepis
Derivatives, Fair Value [Line Items]
Gain on derivative used in net investment hedge	57.0
Net investment hedge
Derivatives, Fair Value [Line Items]
Derivative qualifying as hedge gain (loss), excluded component, after tax			(3.6)
Samsung Bioepis
Derivatives, Fair Value [Line Items]
Ownership percentage before additional purchase transaction					5.00%
Ownership percentage				49.90%		15.00%
Not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount	1,301.5	1,238.8
Foreign Exchange Forward
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) on derivative instruments	$ (34.8)	$ 8.6	53.8
Foreign Exchange Forward \| Net investment hedge
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) on derivative instruments			$ 10.6
Minimum
Derivatives, Fair Value [Line Items]
Range of durations of foreign currency forward contracts	1 month	1 month
Maximum
Derivatives, Fair Value [Line Items]
Range of durations of foreign currency forward contracts	12 months	12 months

Collaborative and Other Relationships - ADUHELM Collaboration Agreement (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2023	Mar. 31, 2023	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Royalty cost of sales				$ 2,533.4	$ 2,278.3	$ 2,109.7
Income (loss) from equity method investments				0.0	2.6	34.9
Regulatory Milestones \| Neurimmune
Collaborative arrangements and non-collaborative arrangement transactions
Upfront and milestone payments made to collaborative partner					100.0
ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Royalty cost of sales	$ 164.0	$ 275.0
Income (loss) from equity method investments				111.0	30.0
ADUHELM \| Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Research and development expense asset acquired					335.0
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments					0.0	$ 45.0
Amounts receivable	1.4			1.4	88.0
Amounts payable	$ 118.4			$ 118.4	81.2
Eisai \| Milestone Payments
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of future development costs				45.00%
Eisai \| Collaboration profit sharing
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense				$ 224.7	233.2
Eisai \| ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments			$ 45.0		59.0
Eisai \| ADUHELM \| Milestone Payments
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense					45.0
Eisai \| ADUHELM \| Inventory, Idle Capacity Charges And Contractual Commitments
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense				$ 197.0	$ 99.0

Share-Based Payments - Market Stock Units Activity (Details) - Market stock units - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares
Beginning balance, unvested (in shares)	113,000
Granted (in shares)	0
Vested (in shares)	(74,000)
Forfeited (in shares)	(5,000)
Ending balance, unvested shares (in shares)	34,000	113,000
Weighted Average Grant Date Fair Value
Beginning balance, unvested (in dollars per share)	$ 366.52	$ 358.77
Granted (in dollars per share)	0		$ 358.77
Vested (in dollars per share)	368.87
Forfeited (in dollars per share)	372.87
Ending balance, unvested (in dollars per share)	$ 359.77	$ 366.52	$ 358.77

Share-Based Payments - Performance Stock Units Settled in Cash Activity (Details) - Performance stock units settled in cash - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares
Beginning balance, unvested (in shares)	83,000
Granted (in shares)	5,000
Vested (in shares)	(41,000)
Forfeited (in shares)	(6,000)
Ending balance, unvested shares (in shares)	41,000	83,000
Total fair value of vested awards	$ 11.7	$ 11.0	$ 9.9

Share-Based Payments - Summary of Share-based Compensation Expense Associated with Each Share-based Compensating Programs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ (274.4)	$ (263.5)	$ (246.6)
Subtotal	668.4	273.6	258.8
Capitalized share-based compensation costs	(10.2)	(9.3)	(8.0)
Share-based compensation expense included in total cost and expense	658.2	264.3	250.8
Market stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	4.9	13.2	45.6
Time-vested restricted stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	220.0	202.3	159.8
Performance stock units settled in stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	35.5	35.0	23.9
Performance stock units settled in cash
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	6.8	10.1	12.2
Employee stock purchase plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	10.5	12.7	17.3
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	3.7	0.3	0.0
Equity Awards Of Acquired Company
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 387.0	$ 0.0	$ 0.0

Segment Information (Tables)

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Geographic information

The following tables contain certain financial information by geographic area:


	December 31, 2023
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	3,141.4	$	2,127.4	$	868.0	$	649.4	$	460.5	$	7,246.7
Revenue from anti-CD20 therapeutic programs	1,618.5		0.4		—		—		70.7		1,689.6
Contract manufacturing, royalty and other revenue	673.6		11.7		—		214.0		—		899.3
Long-lived assets	1,443.0		2,248.0		17.5		8.3		12.9		3,729.7

	December 31, 2022
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	3,469.3	$	2,401.3	$	926.2	$	672.1	$	518.9	$	7,987.8
Revenue from anti-CD20 therapeutic programs	1,636.4		0.1		—		—		64.0		1,700.5
Contract manufacturing, royalty and other revenue	425.8		11.7		—		47.6		—		485.1
Long-lived assets	1,369.4		2,275.8		21.0		13.7		22.6		3,702.5

	December 31, 2021
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	3,805.7	$	2,626.0	$	1,162.4	$	688.0	$	564.8	$	8,846.9
Revenue from anti-CD20 therapeutic programs	1,596.7		—		—		—		61.8		1,658.5
Contract manufacturing, royalty and other revenue	429.9		9.7		—		36.7		—		476.3
Long-lived assets	1,390.5		2,337.8		25.4		16.4		21.7		3,791.8

(1) Represents amounts related to Europe less those attributable to Germany.

Restructuring (Tables)

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Restructuring and Related Costs

Total charges incurred from our 2023 cost saving initiatives are summarized as follows:


	For the Year Ended December 31,
	2023
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total
Selling, general and administrative	$	—	$	23.3	$	23.3
Research and development	—		1.2		1.2
Restructuring charges	153.4		34.6		188.0
Total charges	$	153.4	$	59.1	$	212.5

Total charges incurred from our 2022 cost saving initiatives are summarized as follows:


	For the Years Ended December 31,
	2023						2022
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs(1)		Total
Restructuring charges	$	(2.2)	$	2.6	$	0.4	$	112.6	$	18.5	$	131.1
Total charges	$	(2.2)	$	2.6	$	0.4	$	112.6	$	18.5	$	131.1

(1) Amounts reflect a gain recorded during the third quarter of 2022 of approximately $5.3 million related to the partial termination of a portion of our lease located at 300 Binney Street. For additional information on our 300 Binney Street lease modification, please read Note 12, Leases, to these consolidated financial statements.

Schedule of Restructuring Reserve by Type of Cost

Charges and spending related to our 2023 and 2022 workforce reductions and Reata integration are summarized as follows:


(In millions)	Total
Restructuring reserve, December 31, 2021	$	—
Expense	112.6
Payment	(78.0)
Foreign currency and other adjustments	1.3
Restructuring reserve, December 31, 2022	35.9
Expense	181.6
Payment	(140.5)
Foreign currency and other adjustments	(1.6)
Restructuring reserve, December 31, 2023	$	75.4

Restructuring, Business Transformation and Other Cost Saving Initiatives - Total Charges cost saving initiative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 218.8	$ 131.1	$ 0.0
Severance Costs \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring charges		(2.2)	112.6
Severance Costs \| 2022 Cost Saving Initiative \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges		(2.2)	112.6
Accelerated Depreciation and Other Costs \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring charges		2.6	18.5
Accelerated Depreciation and Other Costs \| 2022 Cost Saving Initiative \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges		2.6	18.5
Gain (Loss) on Termination of Lease	$ 5.3
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring charges		181.6	112.6
Workforce Reduction \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.4	131.1
Workforce Reduction \| 2022 Cost Saving Initiative \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 0.4	$ 131.1

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Other Consolidated Financial Statement Detail - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Litigation settlement agreement and settlement fees	$ 900.0	$ 0.0	$ 917.0	$ 0.0
Net unrealized (gains) losses recognized on equity securities		270.0	264.7	$ 831.4
Other long-term liabilities		781.1	944.2
Accrued income taxes		403.2	541.7
Ionis, Sangamo, Denali and Sage
Business Acquisition [Line Items]
Net unrealized (gains) losses recognized on equity securities		$ 248.5
Denali And Sangamo
Business Acquisition [Line Items]
Net unrealized (gains) losses recognized on equity securities			(278.0)
Ionis And Sage
Business Acquisition [Line Items]
Net unrealized (gains) losses recognized on equity securities			$ 27.3

Collaborative and Other Relationships - Summary of Activity Related to Aducanumab Collaboration (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	$ 0.0	$ 2.6	$ 34.9
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	$ 186.0	173.6	161.5
Total ADUHELM Collaboration third party milestones		0.0	100.0
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income		0.0	45.0
Aducanumab \| Research and development \| Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration		149.4	183.7
Expense reflected within statements of income		82.2	101.1
Aducanumab \| Selling, general and administrative \| Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration		134.2	562.3
Expense reflected within statements of income		$ 71.5	$ 301.4

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 1,049.9	$ 3,419.3
Marketable securities	0.0	1,473.5
Accounts receivable, net of allowance for doubtful accounts of $2.4 and $2.3, respectively	1,664.1	1,705.0
Due from anti-CD20 therapeutic programs	435.9	431.4
Inventory	2,527.4	1,344.4
Other current assets	1,182.0	1,417.6
Total current assets	6,859.3	9,791.2
Marketable securities	0.0	705.7
Property, plant and equipment, net	3,309.7	3,298.6
Operating lease assets	420.0	403.9
Intangible assets, net	8,363.0	1,850.1
Goodwill	6,219.2	5,749.0
Deferred tax asset	928.6	1,226.4
Investments and other assets	745.0	1,529.2
Total assets	26,844.8	24,554.1
Current liabilities:
Current portion of term loan	150.0	0.0
Taxes payable	257.4	259.9
Accounts payable	403.3	491.5
Accrued expense and other	2,623.6	2,521.4
Total current liabilities	3,434.3	3,272.8
Notes payable and term loan	6,788.2	6,281.0
Deferred tax liability	641.8	334.7
Long-term operating lease liabilities	400.0	333.0
Other long-term liabilities	781.1	944.2
Total liabilities	12,045.4	11,165.7
Commitments, contingencies and guarantees (Notes 22 and 23)
Biogen Inc. shareholders’ equity
Preferred stock, par value $0.001 per share	0.0	0.0
Common stock, par value $0.0005 per share	0.1	0.1
Additional paid-in capital	302.5	73.3
Accumulated other comprehensive income (loss)	(153.7)	(164.9)
Retained earnings	17,627.6	16,466.5
Treasury stock, at cost; 23.8 million and 23.8 million shares, respectively	(2,977.1)	(2,977.1)
Total Biogen Inc. shareholders’ equity	14,799.4	13,397.9
Noncontrolling interests	0.0	(9.5)
Total equity	14,799.4	13,388.4
Total liabilities and equity	$ 26,844.8	$ 24,554.1

Leases - Narrative (Details) $ in Millions	1 Months Ended
Leases - Narrative (Details) $ in Millions	Sep. 30, 2022 USD ($)	Dec. 31, 2023 USD ($)	Sep. 27, 2023 USD ($)	Sep. 26, 2023 USD ($) ft²	Dec. 31, 2022 USD ($)
Operating Leased Assets [Line Items]
Operating lease assets		$ 420.0			$ 403.9
Present value of operating lease liabilities		490.3			$ 430.2
Operating Lease, Right-Of-Use Asset, Derecognized	$ 47.4
Operating Lease, Liability, Derecognized	52.7
Gain due to lease termination	$ 5.3
Reata Pharmaceuticals, Inc
Operating Leased Assets [Line Items]
Operating lease, contract term				16 years
Operating lease area \| ft²				327,400
Operating lease liabilities		151.8	$ 151.8	$ 151.8
Remaining lease term				15 years
Operating lease assets		$ 121.2	$ 121.2	$ 122.4
Buildings
Operating Leased Assets [Line Items]
Operating lease, contract term		5 years 6 months
Operating lease assets		$ 168.2
Present value of operating lease liabilities		$ 168.2
Minimum
Operating Leased Assets [Line Items]
Operating lease, contract term		1 year
Operating lease, renewal term		1 year
Minimum \| Sublease
Operating Leased Assets [Line Items]
Operating lease, contract term		1 year
Maximum
Operating Leased Assets [Line Items]
Operating lease, contract term		15 years
Operating lease, renewal term		10 years
Maximum \| Sublease
Operating Leased Assets [Line Items]
Operating lease, contract term		6 years

Share-Based Payments - Performance Stock Units Settled in Stock Activity (Details) - Performance stock units settled in stock - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares
Beginning balance, unvested (in shares)	336,000
Granted (in shares)	206,000
Vested (in shares)	(100,000)
Forfeited (in shares)	(53,000)
Ending balance, unvested shares (in shares)	389,000	336,000
Weighted Average Grant Date Fair Value
Beginning balance, unvested (in dollars per share)	$ 292.95
Granted (in dollars per share)	383.61	$ 294.43	$ 276.61
Vested (in dollars per share)	290.72
Forfeited (in dollars per share)	323.52
Ending balance, unvested (in dollars per share)	$ 325.73	$ 292.95

Equity - Narrative (Details) - USD ($)	12 Months Ended
Equity - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 31, 2020
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	8,000,000
Preferred stock, shares issued (in shares)	0	0	0
Preferred stock, shares outstanding (in shares)	0	0	0
Repurchase of common stock, at cost (in shares)	0
Payments for repurchase of common stock	$ 0	$ 750,000,000.0	$ 1,800,000,000
2020 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases				$ 5,000,000,000
Repurchase of common stock, at cost (in shares)		3,600,000	6,000,000
Payments for repurchase of common stock		$ 750,000,000	$ 1,800,000,000
Remaining authorized amount of share repurchases	$ 2,100,000,000
Series A
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1,750,000
Series X junior participating
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1,000,000
Undesignated
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	5,250,000

Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 371.9	$ 347.2	$ 323.0
Expense reflected within statements of income	186.0	173.6	161.5
Selling, general and administrative \| E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	152.2	52.3	13.6
Expense incurred by the collaboration	$ 304.4	$ 104.6	$ 27.2

Employee Benefit Plans

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Employee Benefit Plans


Note 24:			Employee Benefit Plans

We sponsor various retirement and pension plans. Our estimates of liabilities and expense for these plans incorporate a number of assumptions, including expected rates of return on plan assets and interest rates used to discount future benefits.

401(k) Savings Plan

We maintain a 401(k) Savings Plan, which is available to substantially all regular employees in the U.S. over the age of 21. Participants may make voluntary contributions. We make matching contributions according to the 401(k) Savings Plan’s matching formula. All matching contributions and participant contributions vest immediately. The 401(k) Savings Plan also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement Plan. The expense related to our 401(k) Savings Plan primarily consists of our matching contributions.

Expense related to our 401(k) Savings Plan totaled approximately $55.9 million, $56.0 million and $58.4 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Deferred Compensation Plan

We maintain a non-qualified deferred compensation plan, known as the SSP, which allows a select group of management employees in the U.S. to defer a portion of their compensation. The SSP also provides certain credits to highly compensated U.S. employees that are paid by the company. These credits are known as the Restoration Match. The deferred compensation amounts are accrued when earned. Such deferred compensation is distributable in cash in accordance with the rules of the SSP. Deferred compensation amounts under such plan as of December 31, 2023 and 2022, totaled approximately $134.6 million and $131.9 million, respectively, and are included in other long-term liabilities in our consolidated balance sheets. The SSP also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement Plan. The Restoration Match and participant contributions vest immediately. Distributions to participants can be either in one lump sum payment or annual installments as elected by the participants.

Pension Plans

Our retiree benefit plans include defined benefit plans for employees in our affiliates in Switzerland and Germany as well as other insignificant defined benefit plans in certain other countries where we maintain an operating presence.

Our Swiss plan is a government-mandated retirement fund that provides employees with a minimum investment return. The minimum investment return is determined annually by the Swiss government and was 1.75% in 2023, 2.00% in 2022 and 1.00% in 2021. Under the Swiss plan, both we and certain of our employees with annual earnings in excess of government determined amounts are required to make contributions into a fund managed by an independent investment fiduciary. Employer contributions must be in an amount at least equal to the employee’s contribution. Minimum employee contributions are based on the respective employee’s age, salary and gender. As of December 31, 2023 and 2022, the Swiss plan had an unfunded net pension obligation of $51.5 million and $49.9 million, respectively, and plan assets that totaled $239.6 million and $193.7 million, respectively. In 2023, 2022 and 2021 we recognized net expense totaling $17.6 million, $20.0 million and $21.5 million, respectively, related to our Swiss plan, of which $5.1 million, $5.3 million and $3.5 million, respectively, was included in other (income) expense, net in our consolidated statements of income.

The obligations under the German plans are unfunded and totaled $46.5 million and $40.9 million as of December 31, 2023 and 2022, respectively. Net periodic pension cost related to the German plans totaled $3.6 million, $5.9 million and $7.6 million for the years ended December 31, 2023, 2022 and 2021, respectively, of which $0.8 million, $1.8 million and $2.1 million, respectively, was included in other (income) expense, net in our consolidated statements of income.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (q)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Collaborative and Other Relationships - Eisai (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Jul. 31, 2023	Mar. 31, 2023
LEQEMBI Collaboration
Collaborative arrangements and non-collaborative arrangement transactions
Share of non-controling interest recognized	50.00%	50.00%
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Accrued payment to termination agreement			$ 31.0
Payments made to termination agreement	$ 16.0
Related cost-sharing reduction (as a percentage)	80.00%
Eisai \| LEQEMBI Collaboration \| Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Term of collaboration agreement	5 years
Eisai \| LEQEMBI Collaboration \| Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Term of collaboration agreement	10 years

Leases - Operating Lease Weighted Average Remaining Term and Discount Rate (Details)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term in years	7 years 4 months 13 days	4 years 7 months 20 days
Weighted average discount rate	4.50%	3.70%

Revenue (Tables)

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Abstract]

Revenue by product

Revenue by product are summarized as follows:


	For the Years Ended December 31,
	2023						2022						2021
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	263.1	$	749.4	$	1,012.5	$	417.7	$	1,026.2	$	1,443.9	$	680.6	$	1,271.3	$	1,951.9
VUMERITY	512.1		64.2		576.3		521.3		32.1		553.4		408.9		1.5		410.4
Total Fumarate	775.2		813.6		1,588.8		939.0		1,058.3		1,997.3		1,089.5		1,272.8		2,362.3
AVONEX	536.7		274.3		811.0		649.2		324.3		973.5		830.2		378.5		1,208.7
PLEGRIDY	126.2		168.5		294.7		148.4		183.5		331.9		152.9		204.5		357.4
Total Interferon	662.9		442.8		1,105.7		797.6		507.8		1,305.4		983.1		583.0		1,566.1
TYSABRI	997.9		879.0		1,876.9		1,123.4		907.5		2,030.9		1,142.2		920.9		2,063.1
FAMPYRA	—		90.5		90.5		—		96.6		96.6		—		105.2		105.2
Subtotal: Multiple Sclerosis	2,436.0		2,225.9		4,661.9		2,860.0		2,570.2		5,430.2		3,214.8		2,881.9		6,096.7

Rare Disease:
SPINRAZA	610.5		1,130.7		1,741.2		600.2		1,193.3		1,793.5		587.9		1,317.2		1,905.1
QALSODY(1)	5.8		0.1		5.9		—		—		—		—		—		—
SKYCLARYS(2)	55.9		—		55.9		—		—		—		—		—		—
Subtotal: Rare Disease	672.2		1,130.8		1,803.0		600.2		1,193.3		1,793.5		587.9		1,317.2		1,905.1

Biosimilars:
BENEPALI	—		438.8		438.8		—		441.0		441.0		—		498.3		498.3
IMRALDI	—		222.1		222.1		—		224.5		224.5		—		233.4		233.4
FLIXABI	—		77.4		77.4		—		81.3		81.3		—		99.4		99.4
BYOOVIZ(3)	29.2		2.5		31.7		4.3		—		4.3		—		—		—
Subtotal: Biosimilars	29.2		740.8		770.0		4.3		746.8		751.1		—		831.1		831.1

Other(4)	4.0		7.8		11.8		4.8		8.2		13.0		3.0		11.0		14.0
Total product revenue	$	3,141.4	$	4,105.3	$	7,246.7	$	3,469.3	$	4,518.5	$	7,987.8	$	3,805.7	$	5,041.2	$	8,846.9

(1) QALSODY became commercially available in the U.S. during the second quarter of 2023.

(3) BYOOVIZ became commercially available in the U.S. during the third quarter of 2022 and commercially available in certain international markets in 2023.

(4) Other includes FUMADERM, ADUHELM and ZURZUVAE, which became commercially available in the U.S. during the fourth quarter of 2023.

Analysis of change in reserves

An analysis of the change in reserves for discounts and allowances is summarized as follows:


	December 31, 2023
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	153.8	$	857.7	$	23.5	$	1,035.0
Current provisions relating to sales in current year	735.6		2,720.1		19.0		3,474.7
Adjustments relating to prior years	(0.4)		(38.4)		19.2		(19.6)
Payments/credits relating to sales in current year	(572.9)		(1,944.8)		(2.1)		(2,519.8)
Payments/credits relating to sales in prior years	(142.8)		(737.5)		(28.0)		(908.3)
Ending balance	$	173.3	$	857.1	$	31.6	$	1,062.0


	December 31, 2022
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	137.7	$	759.6	$	38.0	$	935.3
Current provisions relating to sales in current year	666.6		2,715.5		12.3		3,394.4
Adjustments relating to prior years	(2.8)		1.4		(7.2)		(8.6)
Payments/credits relating to sales in current year	(514.9)		(2,060.7)		(1.2)		(2,576.8)
Payments/credits relating to sales in prior years	(132.8)		(558.1)		(18.4)		(709.3)
Ending balance	$	153.8	$	857.7	$	23.5	$	1,035.0


	December 31, 2021
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	141.4	$	1,093.0	$	41.6	$	1,276.0
Current provisions relating to sales in current year	736.7		2,948.7		15.2		3,700.6
Adjustments relating to prior years	(4.0)		(96.1)		(3.3)		(103.4)
Payments/credits relating to sales in current year	(599.3)		(2,283.1)		(0.4)		(2,882.8)
Payments/credits relating to sales in prior years	(137.1)		(902.9)		(15.1)		(1,055.1)
Ending balance	$	137.7	$	759.6	$	38.0	$	935.3

Total reserves included in consolidated balance sheet

The total reserves above, which are included in our consolidated balance sheets, are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Reduction of accounts receivable	$	135.5	$	143.4
Component of accrued expense and other	926.5		891.6
Total revenue-related reserves	$	1,062.0	$	1,035.0

Revenues from anti-CD20 therapeutic programs

Revenue from anti-CD20 therapeutic programs is summarized in the table below. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Royalty revenue on sales of OCREVUS	$	1,266.2	$	1,136.3	$	991.7
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4		547.0		647.7
Other revenue from anti-CD20 therapeutic programs	14.0		17.2		19.1
Total revenue from anti-CD20 therapeutic programs	$	1,689.6	$	1,700.5	$	1,658.5

(1) LUNSUMIO became commercially available in the U.S. during the first quarter of 2023.

Revenue from anti-CD20 therapeutic programs is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Royalty revenue on sales of OCREVUS	$	1,266.2	$	1,136.3	$	991.7
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4		547.0		647.7
Other revenue from anti-CD20 therapeutic programs	14.0		17.2		19.1
Total revenue from anti-CD20 therapeutic programs	$	1,689.6	$	1,700.5	$	1,658.5

(1) LUNSUMIO became commercially available in the U.S. during the first quarter of 2023.

Other revenues

is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021




Contract manufacturing revenue	$	848.2	$	417.7	$	427.7
Royalty and other revenue	51.1		67.4		48.6
Total contract manufacturing, royalty and other revenue	$	899.3	$	485.1	$	476.3

Derivative Instruments - Summary of the Fair Value for our Outstanding Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Other current assets \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Asset derivative instruments	$ 0.3	$ 37.9
Other current assets \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Asset derivative instruments	11.6	25.1
Accrued expense and other \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Liability derivative instruments	26.5	18.4
Accrued expense and other \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Liability derivative instruments	$ 5.1	$ 7.6

Collaborative and Other Relationships - Mosunetuzumab (Details) - Mosunetuzumab - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Option exercise fee	$ 30.0
Development of product candidate expense			$ 20.0
Percentage of future development costs		30.00%	30.00%
Research and development expense asset acquired		$ 28.4
Sales and marketing expense		$ 13.0

Fair Value Measurements - Summary of Assets and Liabilities Recorded at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Feb. 29, 2012
Assets:
Marketable debt securities		$ 2,179.2
Samsung Bioepis
Liabilities:
Ownership percentage			49.90%	15.00%
Fair value, measurements, recurring
Assets:
Cash equivalents	$ 610.7	2,847.6
Marketable equity securities	416.8	791.1
Derivative contracts	11.9	63.0
Plan assets for deferred compensation	37.5	32.8
Total	1,506.9	7,117.9
Liabilities:
Derivative contracts	31.6	26.0
Total	31.6	26.0
Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	430.0	798.8
Receivable from Samsung BioLogics		405.4
Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities		1,231.6
Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities		810.3
Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities		137.3
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	416.8	791.1
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	416.8	791.1
Liabilities:
Derivative contracts	0.0	0.0
Total	0.0	0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	0.0	0.0
Receivable from Samsung BioLogics		0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities		0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities		0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities		0.0
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring
Assets:
Cash equivalents	610.7	2,847.6
Marketable equity securities	0.0	0.0
Derivative contracts	11.9	63.0
Plan assets for deferred compensation	37.5	32.8
Total	660.1	5,122.6
Liabilities:
Derivative contracts	31.6	26.0
Total	31.6	26.0
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	0.0	0.0
Receivable from Samsung BioLogics		0.0
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities		1,231.6
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities		810.3
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities		137.3
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	0.0	0.0
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	430.0	1,204.2
Liabilities:
Derivative contracts	0.0	0.0
Total	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	$ 430.0	798.8
Receivable from Samsung BioLogics		405.4
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities		0.0
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities		0.0
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities		$ 0.0

Share-Based Payments - Employee Stock Options (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance, outstanding shares (in shares)	81,000
Stock options granted (in shares)	0
Exercised (in shares)	0
Forfeited (in shares)	0
Ending balance, outstanding shares (in shares)	81,000	81,000
Weighted Average Exercise Price
Beginning balance, weighted average exercise price (in dollars per share)	$ 301.85
Granted (in dollars per share)	0
Exercised (in dollars per share)	0
Forfeited (in dollars per share)	0
Ending balance, weighted average exercise price (in dollars per share)	$ 301.85	$ 301.85
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract]
Options exercisable (in shares)	27,000
Options exercisable (in dollars per share)	$ 301.85
Weighted average remaining contractual term for options outstanding	8 years 10 months 24 days	9 years 10 months 24 days
Weighted average remaining contractual term for options exercisable	8 years 10 months 24 days

Indebtedness (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Summary of indebtedness

Our indebtedness is summarized as follows:


	As of December 31,
(In millions)	2023		2022
Current portion:
2023 Term Loan 364-day tranche(1)	$	150.0	$	—
Current portion of notes payable and term loan	$	150.0	$	—
Non-current portion:
2023 Term Loan three-year tranche(1)	$	500.0	$	—
4.050% Senior Notes due September 15, 2025	1,746.6		1,744.7
2.250% Senior Notes due May 1, 2030	1,493.8		1,492.9
5.200% Senior Notes due September 15, 2045	1,100.7		1,100.3
3.150% Senior Notes due May 1, 2050	1,474.3		1,473.8
3.250% Senior Notes due February 15, 2051	472.8		469.3
Non-current portion of notes payable and term loan	$	6,788.2	$	6,281.0

Total debt maturities

The total gross payments due under our debt arrangements are as follows:


(In millions)	As of December 31, 2023
2024	$	150.0
2025	1,750.0
2026	500.0
2027	—
2028	—
2029 and thereafter	4,817.3
Total current and non-current debt	$	7,217.3
Less: debt discount and issuance fees	(279.1)
Total current and non-current debt, net	$	6,938.2

Income Taxes - Income Before Income Tax Provision and the Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income before income tax (benefit) expense:
Domestic	$ 192.4	$ 1,842.0	$ 448.3
Foreign	1,104.4	1,749.8	1,296.9
Income before income tax (benefit) expense and equity in loss of investee, net of tax	1,296.8	3,591.8	1,745.2
Current:
Federal	377.6	694.5	319.1
State	15.1	39.0	23.1
Foreign	48.4	67.9	137.1
Total current	441.1	801.4	479.3
Deferred:
Federal	(587.4)	(328.3)	(242.5)
State	(12.7)	2.5	(11.9)
Foreign	294.3	157.2	(172.4)
Total deferred	(305.8)	(168.6)	(426.8)
Total income tax (benefit) expense	$ 135.3	$ 632.8	$ 52.5

Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 13,388.4	$ 10,959.7	$ 10,686.1
Net current period other comprehensive income (loss)	11.2	(58.2)	192.9
Ending balance	14,799.4	13,388.4	10,959.7
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(164.9)	(106.7)	(299.0)
Other comprehensive income (loss) before reclassifications	11.1	87.0	134.1
Amounts reclassified from AOCI	0.1	(145.2)	58.2
Net current period other comprehensive income (loss)	11.2	(58.2)	192.3
Ending balance	(153.7)	(164.9)	(106.7)
Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(15.7)	(2.2)	1.4
Other comprehensive income (loss) before reclassifications	2.3	(23.5)	(6.6)
Amounts reclassified from AOCI	13.4	10.0	3.0
Net current period other comprehensive income (loss)	15.7	(13.5)	(3.6)
Ending balance	0.0	(15.7)	(2.2)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	15.1	53.8	(179.0)
Other comprehensive income (loss) before reclassifications	(26.8)	137.3	178.2
Amounts reclassified from AOCI	(13.3)	(176.0)	54.6
Net current period other comprehensive income (loss)	(40.1)	(38.7)	232.8
Ending balance	(25.0)	15.1	53.8
Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.0	25.5	(8.5)
Other comprehensive income (loss) before reclassifications		12.6	33.4
Amounts reclassified from AOCI		(38.1)	0.6
Net current period other comprehensive income (loss)		(25.5)	34.0
Ending balance		0.0	25.5
Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1.1)	(44.8)	(66.3)
Other comprehensive income (loss) before reclassifications	(1.5)	43.7	21.5
Amounts reclassified from AOCI	0.0	0.0	0.0
Net current period other comprehensive income (loss)	(1.5)	43.7	21.5
Ending balance	(2.6)	(1.1)	(44.8)
Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(163.2)	(139.0)	(46.6)
Other comprehensive income (loss) before reclassifications	37.1	(83.1)	(92.4)
Amounts reclassified from AOCI	0.0	58.9	0.0
Net current period other comprehensive income (loss)	37.1	(24.2)	(92.4)
Ending balance	$ (126.1)	$ (163.2)	$ (139.0)

Segment Information - Narrative (Details) $ in Millions	12 Months Ended
Segment Information - Narrative (Details) $ in Millions	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Revenue from External Customer [Line Items]
Number of reportable segment \| segment	1
Other long-lived assets	$ 3,729.7	$ 3,702.5	$ 3,791.8
Solothurn, Switzerland
Revenue from External Customer [Line Items]
Other long-lived assets	$ 2,156.4	$ 2,198.5	$ 2,237.0

Inventory - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
Inventory - Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Inventory [Line Items]
Write-downs on excess, obsolete, unmarketable or other inventory				$ 124.4	$ 336.2	$ 167.6
Income (loss) from equity method investments				$ 0.0	2.6	34.9
Eisai
Inventory [Line Items]
Income (loss) from equity method investments					0.0	$ 45.0
Eisai \| Milestone Payments
Inventory [Line Items]
Percentage of future development costs				45.00%
ADUHELM
Inventory [Line Items]
Write-downs on excess, obsolete, unmarketable or other inventory		$ 275.0	$ 120.0
Income (loss) from equity method investments				$ 111.0	30.0
ADUHELM \| Eisai
Inventory [Line Items]
Income (loss) from equity method investments	$ 45.0				$ 59.0
ADUHELM \| Centers for Medicare and Medicaid Service \| Eisai
Inventory [Line Items]
Income (loss) from equity method investments				$ 136.0

Other Consolidated Financial Statement Detail - Accrued Expense and Other (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	$ 1,062.0	$ 1,035.0	$ 935.3	$ 1,276.0
Reata acquisition-related accrued expense	117.5	0.0
Total accrued expense and other	2,623.6	2,521.4
Component of accrued expense and other
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	926.5	891.6
Employee compensation and benefits	335.1	395.6
Collaboration expense	214.6	277.9
Royalties and licensing fees	191.5	209.4
Other	$ 838.4	$ 746.9

Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Millions	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Retained earnings	Treasury stock	Total Biogen Inc. shareholders’ equity	Noncontrolling interests	2020 Share Repurchase Program	2020 Share Repurchase Program Common stock	2020 Share Repurchase Program Additional paid-in capital	2020 Share Repurchase Program Retained earnings	2020 Share Repurchase Program Treasury stock	2020 Share Repurchase Program Total Biogen Inc. shareholders’ equity
Common stock outstanding, beginning balance (in shares) at Dec. 31, 2020		176,200
Beginning balance at Dec. 31, 2020	$ 10,686.1	$ 0.1	$ 0.0	$ (299.0)	$ 13,976.3	$ (2,977.1)	$ 10,700.3	$ (14.2)
Treasury stock at cost, beginning balance (in shares) at Dec. 31, 2020						23,800
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,727.6				1,556.1		1,556.1	171.5
Other comprehensive income (loss), net of tax	192.9			192.3			192.3	0.6
Distribution to noncontrolling interest	(100.0)							(100.0)
Capital contribution from noncontrolling interest	5.6							5.6
Repurchase of common stock pursuant to the share repurchase program, at cost (in shares)									(6,000)				(6,000)
Repurchase of common stock pursuant to the share repurchase program, at cost									$ (1,800.0)				$ (1,800.0)	$ (1,800.0)
Retirement of common stock pursuant to the share repurchase program, at cost (in shares)										6,000			6,000
Retirement of common stock pursuant to the share repurchase program, at cost									$ 0.0		$ (231.9)	$ (1,568.1)	$ 1,800.0
Issuance of common stock under stock option and stock purchase plans (in shares)		200
Issuance of common stock under stock option and stock purchase plans	54.4		54.4				54.4
Issuance of common stock under stock award plan (in shares)		400
Issuance of common stock under stock award plan	(55.0)		(2.4)		(52.6)		(55.0)
Compensation expense related to share-based payments	246.6		246.6				246.6
Other	$ 1.5		1.5				1.5
Common stock outstanding, ending balance (in shares) at Dec. 31, 2021	147,000	170,800
Ending balance at Dec. 31, 2021	$ 10,959.7	$ 0.1	68.2	(106.7)	13,911.7	$ (2,977.1)	10,896.2	63.5
Treasury stock at cost, ending balance (in shares) at Dec. 31, 2021						23,800
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,961.6				3,046.9		3,046.9	(85.3)
Other comprehensive income (loss), net of tax	(58.2)			(58.2)			(58.2)
Capital contribution from noncontrolling interest	12.3							12.3
Repurchase of common stock pursuant to the share repurchase program, at cost (in shares)									(3,600)				(3,600)
Repurchase of common stock pursuant to the share repurchase program, at cost									$ (750.0)				$ (750.0)	$ (750.0)
Retirement of common stock pursuant to the share repurchase program, at cost (in shares)										3,600			3,600
Retirement of common stock pursuant to the share repurchase program, at cost									$ 0.0		$ (257.9)	$ (492.1)	$ 750.0
Issuance of common stock under stock option and stock purchase plans (in shares)		200
Issuance of common stock under stock option and stock purchase plans	44.2		44.2				44.2
Issuance of common stock under stock award plan (in shares)		500
Issuance of common stock under stock award plan	(46.0)		(46.0)				(46.0)
Compensation expense related to share-based payments	263.5		263.5				263.5
Other	$ 1.3		1.3				1.3
Common stock outstanding, ending balance (in shares) at Dec. 31, 2022	144,000	167,900
Ending balance at Dec. 31, 2022	$ 13,388.4	$ 0.1	73.3	(164.9)	16,466.5	$ (2,977.1)	13,397.9	(9.5)
Treasury stock at cost, ending balance (in shares) at Dec. 31, 2022	23,800					23,800
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 1,161.5				1,161.1		1,161.1	0.4
Other comprehensive income (loss), net of tax	11.2			11.2			11.2
Distribution to noncontrolling interest	(3.2)							(3.2)
Capital contribution from noncontrolling interest	$ 12.3							12.3
Repurchase of common stock pursuant to the share repurchase program, at cost (in shares)	0
Issuance of common stock under stock option and stock purchase plans (in shares)		200
Issuance of common stock under stock option and stock purchase plans	$ 45.1		45.1				45.1
Issuance of common stock under stock award plan (in shares)		600
Issuance of common stock under stock award plan	(89.5)		(89.5)				(89.5)
Compensation expense related to share-based payments	274.4		274.4				274.4
Other	$ (0.8)		(0.8)				(0.8)
Common stock outstanding, ending balance (in shares) at Dec. 31, 2023	144,900	168,700
Ending balance at Dec. 31, 2023	$ 14,799.4	$ 0.1	$ 302.5	$ (153.7)	$ 17,627.6	$ (2,977.1)	$ 14,799.4	$ 0.0
Treasury stock at cost, ending balance (in shares) at Dec. 31, 2023	23,800					23,800

Collaborative and Other Relationships (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Co-promotion profit sharing formula

As a result of the FDA approval of LUNSUMIO our share of the combined annual co-promotion profits for RITUXAN and LUNSUMIO in excess of $50.0 million varies upon the following events, as summarized in the table below:




After LUNSUMIO Approval until the First Threshold Date	37.5	%
After First Threshold Date until the Second Threshold Date	35.0	%
After Second Threshold Date	30.0	%

Pretax profit sharing formula

Our share of annual co-promotion profits in excess of $50.0 million varies upon the following events, as summarized in the table below:



Until Second GAZYVA Threshold Date	37.5	%
After Second GAZYVA Threshold Date	35.0	%

Revenues from anti-CD20 therapeutic programs

Revenue from anti-CD20 therapeutic programs is summarized in the table below. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Royalty revenue on sales of OCREVUS	$	1,266.2	$	1,136.3	$	991.7
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4		547.0		647.7
Other revenue from anti-CD20 therapeutic programs	14.0		17.2		19.1
Total revenue from anti-CD20 therapeutic programs	$	1,689.6	$	1,700.5	$	1,658.5

(1) LUNSUMIO became commercially available in the U.S. during the first quarter of 2023.

Revenue from anti-CD20 therapeutic programs is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Royalty revenue on sales of OCREVUS	$	1,266.2	$	1,136.3	$	991.7
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4		547.0		647.7
Other revenue from anti-CD20 therapeutic programs	14.0		17.2		19.1
Total revenue from anti-CD20 therapeutic programs	$	1,689.6	$	1,700.5	$	1,658.5

(1) LUNSUMIO became commercially available in the U.S. during the first quarter of 2023.

Summary of activity related to BAN2401 and Elenbecestat collaboration

A summary of development and sales and marketing expense related to the LEQEMBI Collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	371.9	$	347.2	$	323.0
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our consolidated statements of income	186.0		173.6		161.5
Total sales and marketing expense incurred by the LEQEMBI Collaboration	304.4		104.6		27.2
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	152.2		52.3		13.6

Summary of activity related to Aducanumab collaboration

A summary of development expense, sales and marketing expense and milestone payments related to our initial ADUHELM Collaboration Agreement is as follows:


	For the Year Ended December 31,
(In millions)	2022		2021
Total ADUHELM Collaboration development expense	$	149.4	$	183.7
Biogen's share of the ADUHELM Collaboration development expense reflected in research and development expense in our consolidated statements of income	82.2		101.1
Total sales and marketing expense incurred by the ADUHELM Collaboration	134.2		562.3
Biogen's share of the ADUHELM Collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	71.5		301.4
Total ADUHELM Collaboration third party milestones	—		100.0
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	—		45

Summary of activity related to the UCB collaboration

A summary of development expense related to the UCB collaboration agreement is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total UCB collaboration development expense	$	60.7	$	68.0	$	84.2
Biogen's share of the UCB collaboration development expense reflected in research and development expense in our consolidated statements of income	30.3		34.0		42.1

Summary of Activity Related to Sage Therapeutics

A summary of development and sales and marketing expense related to the Sage collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total Sage collaboration development expense	$	176.7	$	173.3	$	167.7
Biogen's share of the Sage collaboration development expense reflected in research and development expense in our consolidated statements of income	88.3		86.7		83.8
Total sales and marketing expense incurred by the Sage collaboration	187.0		109.9		36.4
Biogen's share of the Sage collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	93.5		55.0		18.2

Summary of Activity Related to Denali Therapeutics Collaboration

A summary of development expense related to the Denali collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total Denali collaboration development expense	$	65.0	$	75.1	$	42.5
Biogen's share of the Denali collaboration development expense reflected in research and development expense in our consolidated statements of income	39.0		43.8		25.5

Summary of Activity Related to Sangamo Therapeutics

A summary of development expense related to the Sangamo collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total Sangamo collaboration development expense	$	4.1	$	19.1	$	22.7
Biogen's share of the Sangamo collaboration development expense reflected in research and development expense in our consolidated statements of income	2.4		12.1		14.6

Other Consolidated Financial Statement Detail - Gain (Loss) on Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net (gains) losses recognized on equity securities	$ 275.2	$ 264.7	$ 821.1
Less: Net (gains) losses realized on equity securities	5.2	0.0	(10.3)
Net unrealized (gains) losses recognized on equity securities	$ 270.0	$ 264.7	$ 831.4

Derivative Instruments

12 Months Ended

Dec. 31, 2023

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments


Note 10:			Derivative Instruments

Foreign Currency Forward Contracts - Hedging Instruments

Due to the global nature of our operations, portions of our revenue and operating expense are recorded in currencies other than the U.S. dollar. The value of revenue and operating expense measured in U.S. dollars is therefore subject to changes in foreign currency exchange rates. We enter into foreign currency forward contracts and foreign currency options with financial institutions with the primary objective to mitigate the impact of foreign currency exchange rate fluctuations on our international revenue and operating expense.

Foreign currency forward contracts and foreign currency options in effect as of December 31, 2023 and 2022, had durations of 1 to 12 months. These contracts have been designated as cash flow hedges and unrealized gains and losses on the portion of these foreign currency forward contracts and foreign currency options that are included in the effectiveness test are reported in AOCI. Realized gains and losses of such contracts and options are recognized in revenue when the sale of product in the currency being hedged is recognized and in operating expense when the expense in the currency being hedged is recorded. We recognize all cash flow hedge reclassifications from AOCI and fair value changes of excluded portions in the same line item in our consolidated statements of income that have been impacted by the hedged item.

The notional amount of foreign currency forward contracts and foreign currency options that were entered into to hedge forecasted revenue and operating expense is summarized as follows:


	Notional Amount As of December 31,
(In millions)	2023		2022
Euro	$	1,169.0	$	1,495.5
British pound	—		162.8
Swiss franc	—		—
Canadian dollar	—		57.2
Total foreign currency forward contracts and options	$	1,169.0	$	1,715.5

The pre-tax portion of the fair value of these foreign currency forward contracts and foreign currency options that were included in AOCI in total equity is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Unrealized gains	$	—	$	29.9	$	60.8
Unrealized (losses)	(34.8)		(21.3)		(7.0)
Net unrealized gains (losses)	$	(34.8)	$	8.6	$	53.8

We expect the net unrealized losses of approximately $34.8 million to be settled over the next 12 months, with any amounts in AOCI to be reported as an adjustment to revenue or operating expense. We consider the impact of our and our counterparties’ credit risk on the fair value of the contracts as well as the ability of each party to execute its contractual obligations. As of December 31, 2023 and 2022, credit risk did not materially change the fair value of our foreign currency forward contracts and forward currency options.

The following table summarizes the effect of foreign currency forward contracts and forward currency options designated as hedging instruments in our consolidated statements of income:


For the Years Ended December 31,
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)							Net Gains/(Losses) Recognized in Operating Income (in millions)
Location	2023		2022		2021		Location	2023		2022		2021
Revenue	$	11.6	$	201.6	$	(60.0)	Revenue	$	(2.4)	$	(8.6)	$	(8.4)
Operating expense	3.7		(5.5)		(0.8)		Operating expense	—		—		—

Net Investment Hedges - Hedging Instruments

In February 2012 we entered into a joint venture agreement with Samsung BioLogics establishing an entity, Samsung Bioepis, to develop, manufacture and market biosimilar products. In June 2018 we exercised our option under our joint venture agreement to increase our ownership percentage in Samsung Bioepis from approximately 5.0% to approximately 49.9%. Our investment in the equity of Samsung Bioepis related to this transaction was exposed to the currency fluctuations in the South Korean won.

In order to mitigate the currency fluctuations between the U.S. dollar and South Korean won, we entered into foreign currency forward contracts. These contracts were designated as net investment hedges. In April 2022 we completed the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics and closed these foreign currency forward contracts. Upon completing this sale, the cumulative gains on our net investment hedges of $57.0 million were reclassified from AOCI and reflected within the total pre-tax gain recognized from the sale, which was recorded in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2022. For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

Prior to the sale of our 49.9% equity interest in Samsung Bioepis, we recognized changes in the spot exchange rate of these foreign currency forward contracts in AOCI. The pre-tax portion of the fair value of these foreign currency forward contracts that were included in AOCI in total equity reflected net gains of $10.6 million as of December 31, 2021. We excluded fair value changes related to the forward rate from our hedging relationship and amortized the

forward points in other (income) expense, net in our consolidated statements of income over the term of the contract. The pre-tax portion of the fair value of the forward points that were included in AOCI in total equity reflected net losses of $3.6 million as of December 31, 2021.

The following table summarizes the effect of our net investment hedges in our consolidated financial statements:


For the Years Ended December 31,
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion) (in millions)			Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions)			Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)
Location	2022		2021		Location	2022		2021		Location	2022		2021
Gains (losses) on net investment hedge(1)	$	20.4	$	46.0	Gains (losses) on net investment hedge(1)	$	(3.2)	$	(3.2)	Other (income) expense(1)	$	(4.6)	$	(0.6)

(1) Beginning in the second quarter of 2022 we no longer held net investment hedges as they were closed with the sale of our 49.9% equity interest in Samsung Bioepis in April 2022. For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Foreign Currency Forward Contracts - Other Derivative Instruments

We also enter into other foreign currency forward contracts, usually with durations of one month or less, to mitigate the foreign currency risk related to certain balance sheet positions. We have not elected hedge accounting for these transactions.

The aggregate notional amount of these outstanding foreign currency forward contracts was $1,301.5 million and $1,238.8 million as of December 31, 2023 and 2022, respectively. Net gains of $3.8 million, net losses of $34.7 million and net losses of $43.3 million related to these contracts were recorded as a component of other (income) expense, net for the years ended December 31, 2023, 2022 and 2021, respectively.

Summary of Derivative Instruments

While certain of our derivative instruments are subject to netting arrangements with our counterparties, we do not offset derivative assets and liabilities in our consolidated balance sheets. The amounts in the table below would not be substantially different if the derivative assets and liabilities were offset.

The following table summarizes the fair value and presentation in our consolidated balance sheets of our outstanding derivative instruments, including those designated as hedging instruments:


		As of December 31,
(In millions)	Balance Sheet Location	2023		2022
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	0.3	$	37.9

Liability derivative instruments	Accrued expense and other	26.5		18.4


Other Derivative Instruments:
Asset derivative instruments	Other current assets	11.6		25.1
Liability derivative instruments	Accrued expense and other	5.1		7.6

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income attributable to Biogen Inc.	$ 1,161.1	$ 3,046.9	$ 1,556.1
Other comprehensive income:
Unrealized gains (losses) on securities available for sale, net of tax	15.7	(13.5)	(3.6)
Unrealized gains (losses) on cash flow hedges, net of tax	(40.1)	(38.7)	232.8
Gains (losses) on net investment hedges, net of tax	0.0	(25.5)	34.0
Unrealized gains (losses) on pension benefit obligation, net of tax	(1.5)	43.7	21.5
Currency translation adjustment	37.1	(24.2)	(92.4)
Total other comprehensive income (loss), net of tax	11.2	(58.2)	192.3
Comprehensive income (loss) attributable to Biogen Inc.	1,172.3	2,988.7	1,748.4
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	0.4	(85.3)	172.1
Comprehensive income (loss)	$ 1,172.7	$ 2,903.4	$ 1,920.5

Insider Trading Arrangements
shares in Thousands

12 Months Ended

Dec. 31, 2023

Trading Arrangements, by Individual

Non-Rule 10b5-1 Arrangement Adopted

false

Rule 10b5-1 Arrangement Terminated

false

Non-Rule 10b5-1 Arrangement Terminated

false

Robin Kramer [Member]

Trading Arrangements, by Individual

Material Terms of Trading Arrangement

From time to time, our officers (as defined in Rule 16a-1(f)) and directors may enter into Rule 10b5-1 or non-Rule 10b5-1 trading arrangements (as each such term is defined in Item 408 of Regulation S-K). During the fourth quarter of 2023 our officers and directors took the following actions with respect to 10b5-1 trading arrangements:

Trading Arrangement

Name and Position

Action

Date

Rule
10b5-1

Non-Rule 10b5-1

Total Shares to be Sold

Expiration Date

Robin Kramer (Senior Vice President, Chief Accounting Officer)

Adopt

11/13/2023

—

1,500

11/10/2025

Name

Robin Kramer

Title

Senior Vice President, Chief Accounting Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

11/13/2023

Arrangement Duration

728 days

Aggregate Available

1,500,000

Inventory

12 Months Ended

Dec. 31, 2023

Inventory Disclosure [Abstract]

Inventory


Note 6:			Inventory

The components of inventory are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Raw materials	$	426.9	$	413.2
Work in process	1,926.8		751.9
Finished goods	255.4		200.4
Total inventory	$	2,609.1	$	1,365.5

Balance Sheet Classification:
Inventory	$	2,527.4	$	1,344.4
Investments and other assets	81.7		21.1
Total inventory	$	2,609.1	$	1,365.5

Long-term inventory is included in investments and other assets in our consolidated balance sheets.

Write Downs and Other Charges

Inventory amounts written down as a result of excess, obsolescence or unmarketability are charged to cost of sales, and totaled $124.4 million, $336.2 million and $167.6 million for the years ended December 31, 2023, 2022 and 2021, respectively.

During the first quarter of 2022 we wrote-off approximately $275.0 million of inventory related to ADUHELM, as a result of the final NCD, which was recognized in cost of sales within our consolidated statements of income for the year ended December 31, 2022. We recognized approximately $136.0 million related to Eisai's 45.0% share of these charges in collaboration profit sharing/(loss reimbursement) within our consolidated statements of income for the year ended December 31, 2022.

During the fourth quarter of 2021 we wrote-off approximately $120.0 million of inventory in excess of forecasted demand related to ADUHELM, which was recognized in cost of sales within our consolidated statements of income for the year ended December 31, 2021. We have recognized approximately $59.0 million related to Eisai's 45.0% share of these charges in collaboration profit sharing/(loss reimbursement) within our consolidated statements of income for the year ended December 31, 2021.

As of December 31, 2023 and 2022, the carrying value of ADUHELM inventory was zero. In November 2023 we notified Neurimmune of our decision to terminate our collaboration and license agreement with Neurimmune and to discontinue the development and commercialization of ADUHELM.

For additional information on our collaboration with Eisai, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements. For additional information on the discontinuation of ADUHELM, please read Note 20, Investments in Variable Interest Entities, to these consolidated financial statements.

Financial Instruments

12 Months Ended

Dec. 31, 2023

Investments, All Other Investments [Abstract]

Financial Instruments


Note 9:			Financial Instruments

The following table summarizes our financial assets with maturities of less than 90 days from the date of purchase included in cash and cash equivalents in our consolidated balance sheets:


	As of December 31,
(In millions)	2023		2022
Commercial paper	$	—	$	177.2
Overnight reverse repurchase agreements	—		59.0
Money market funds	610.7		2,581.5
Short-term debt securities	—		29.9
Total	$	610.7	$	2,847.6

The carrying values of our commercial paper, including accrued interest, overnight reverse repurchase agreements, money market funds and short-term debt securities approximate fair value due to their short-term maturities.

We partially funded our Reata acquisition through available cash, cash equivalents and marketable securities. As of December 31, 2023, we have sold all of our marketable debt securities. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

Our marketable equity securities gains (losses) are recorded in other (income) expense, net in our consolidated statements of income. The following tables summarize our marketable debt and equity securities, classified as available for sale:


	As of December 31, 2023
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value












Marketable equity securities:
Marketable equity securities, current	$	31.6	$	—	$	(21.0)	$	10.6
Marketable equity securities, non-current	948.3		—		(542.1)		406.2
Total marketable equity securities	$	979.9	$	—	$	(563.1)	$	416.8


	As of December 31, 2022
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable debt securities:
Corporate debt securities:
Current	$	936.2	$	—	$	(4.9)	$	931.3
Non-current	305.3		0.1		(5.1)		300.3
Government securities:
Current	547.1		0.1		(5.0)		542.2
Non-current	271.4		—		(3.3)		268.1
Mortgage and other asset backed securities:
Current	—		—		—		—
Non-current	139.1		0.1		(1.9)		137.3
Total marketable debt securities	$	2,199.1	$	0.3	$	(20.2)	$	2,179.2

Marketable equity securities:

Marketable equity securities, non-current	$	1,133.8	$	—	$	(342.7)	$	791.1
Total marketable equity securities	$	1,133.8	$	—	$	(342.7)	$	791.1

Summary of Contractual Maturities: Available-for-Sale Debt Securities

The estimated fair value and amortized cost of our marketable debt securities classified as available-for-sale by contractual maturity are summarized as follows:



	As of December 31, 2022
(In millions)		Estimated Fair Value		Amortized Cost
Due in one year or less		$	1,473.5	$	1,483.3
Due after one year through five years		694.4		703.7
Due after five years		11.3		12.1
Total marketable debt securities		$	2,179.2	$	2,199.1

The average maturity of our marketable debt securities classified as available-for-sale as of December 31, 2022, was approximately 8 months.

Proceeds from Marketable Debt Securities

The proceeds from maturities and sales of marketable debt securities and resulting realized gains and losses are summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Proceeds from maturities and sales	$	7,380.8	$	3,671.0	$	3,405.4
Realized gains	1.4		—		0.2
Realized losses	18.4		12.6		4.0

Realized losses for the year ended December 31, 2023, primarily relate to sales of U.S. treasuries and corporate bonds. Realized losses for the years ended December 31, 2022 and 2021, primarily relate to sales of corporate bonds, agency mortgage-backed securities and other asset-backed securities.

Strategic Investments

Our strategic investment portfolio includes investments in equity securities of certain biotechnology companies, which are reflected within our disclosures included in Note 8, Fair Value Measurements, to these consolidated financial statements, as well as venture capital funds where the underlying investments are in equity securities of certain biotechnology companies and non-marketable equity securities.

As of December 31, 2023, our strategic investment portfolio was comprised of investments totaling $460.7 million which are included in other current assets and investments and other assets in our consolidated balance sheets. As of December 31, 2022, our strategic investment portfolio comprised of investments totaling $846.0 million which are included in investments and other assets in our consolidated balance sheets.

The decrease in our strategic investment portfolio for the year ended December 31, 2023, was primarily due to the decrease in the fair value of our investments in Denali, Sangamo and Sage common stock. Additionally, during 2023 we sold a portion of our Sangamo and Denali common stock and the remainder of our Ionis common stock.

For additional information on our investments in Denali, Sangamo, Sage and Ionis common stock, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Mar. 31, 2023
Variable Interest Entity [Line Items]
Income (loss) from equity method investments		$ 0.0	$ 2.6	$ 34.9
Potential future milestone payments commitment to third party approximately		5,100.0
Deferred tax asset, net			100.0
Valuation allowance		1,278.7	2,003.3		$ 85.0
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities		16.4	27.8
ADUHELM
Variable Interest Entity [Line Items]
Income (loss) from equity method investments		$ 111.0	30.0
Neurimmune
Variable Interest Entity [Line Items]
Research and development costs, percentage		100.00%
Deconsolidation, gain (loss)		$ 3.0
Regulatory Milestones
Variable Interest Entity [Line Items]
Potential future milestone payments commitment to third party approximately		$ 400.0
Eisai
Variable Interest Entity [Line Items]
Income (loss) from equity method investments			0.0	$ 45.0
Eisai \| Milestone Payments
Variable Interest Entity [Line Items]
Percentage of future development costs		45.00%
Eisai \| ADUHELM
Variable Interest Entity [Line Items]
Income (loss) from equity method investments	$ 45.0		$ 59.0
Eisai \| Regulatory Milestones \| Neurimmune \| ADUHELM
Variable Interest Entity [Line Items]
Potential future milestone payments commitment to third party approximately	$ 100.0

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies


Note 22:			Commitments and Contingencies

Royalty Payments

TYSABRI

We are obligated to make contingent payments of 18.0% on annual worldwide net sales of TYSABRI up to $2.0 billion and 25.0% on annual worldwide net sales of TYSABRI that exceed $2.0 billion. Royalty payments are recognized as cost of sales in our consolidated statements of income.

SPINRAZA

We make royalty payments to Ionis on annual worldwide net sales of SPINRAZA using a tiered royalty rate between 11.0% and 15.0%, which are recognized as cost of sales in our consolidated statements of income. For additional information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

QALSODY

We make royalty payments to Ionis on annual worldwide net sales of QALSODY using a tiered royalty rate between 11.0% and 15.0%, which are recognized as cost of sales in our consolidated statements of income.

For additional information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

VUMERITY

We make royalty payments to Alkermes on worldwide net sales of VUMERITY using a royalty rate of 15.0%, which are recognized as cost of sales in our consolidated statements of income. Royalties payable on net sales of VUMERITY are subject, under certain circumstances, to tiered minimum annual payment requirements for a period of five years following FDA approval.

In October 2019 we entered into a new supply agreement and amended our license and collaboration agreement with Alkermes for VUMERITY. We have elected to initiate a technology transfer and, following a transition period, to manufacture VUMERITY or have VUMERITY manufactured by a third party we have engaged in exchange for paying an increased royalty rate to Alkermes on any portion of future worldwide net commercial sales of VUMERITY that is manufactured by us or our designee. For additional information on our collaboration arrangement with Alkermes, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

SKYCLARYS

In connection with our acquisition of Reata in September 2023 we assumed additional contractual obligations related to royalty payments. Reata entered into agreements to pay royalties on future sales of SKYCLARYS, which will cumulatively range in the low- to mid-single digits.

For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

Regulatory and Commercial Milestone Payments

Based on our development plans as of December 31, 2023, we could trigger potential future milestone payments to third parties of up to approximately $5.1 billion, including approximately $0.9 billion in development milestones, approximately $0.4 billion in regulatory milestones and approximately $3.8 billion in commercial milestones, as part of our various collaborations, including licensing and development programs. Payments under these agreements generally become due and payable upon achievement of certain development, regulatory or commercial milestones. Because the achievement of these milestones was not considered probable as of December 31, 2023, such contingencies have not been recorded in our financial statements. Amounts related to contingent milestone payments are not considered contractual obligations as they are contingent on the successful achievement of certain development, regulatory or commercial milestones.

During the fourth quarter of 2023 we accrued a milestone payment due to Sage of $75.0 million upon the first commercial sale of ZURZUVAE for PPD in the U.S., which was recorded within intangible assets, net in our

consolidated balance sheets, and subsequently paid in January 2024. If certain clinical and commercial milestones are met, we may pay up to approximately $109.0 million in milestones in 2024 under our current agreements.

Other Funding Commitments

As of December 31, 2023, we have several ongoing clinical studies in various clinical trial stages. Our most significant clinical trial expenditures are to CROs. The contracts with CROs are generally cancellable, with notice, at our option. We recorded accrued expense of approximately $47.2 million in our consolidated balance sheets for expenditures incurred by CROs as of December 31, 2023. We have approximately $669.0 million in cancellable future commitments based on existing CRO contracts as of December 31, 2023.

Tax Related Obligations

We exclude liabilities pertaining to uncertain tax positions from our summary of contractual obligations as we cannot make a reliable estimate of the period of cash settlement with the respective taxing authorities. As of December 31, 2023, we have approximately $172.0 million of liabilities associated with uncertain tax positions.

As of December 31, 2023 and 2022, we have accrued income tax liabilities of approximately $419.5 million and $558.0 million, respectively, under the Transition Toll Tax. Of the amounts accrued as of December 31, 2023, approximately $185.4 million is expected to be paid within one year. The Transition Toll Tax is being paid in installments over an eight--year period, which started in 2018, and will not accrue interest. For additional information on the Transition Toll Tax, please read Note 17, Income Taxes, to these consolidated financial statements.

Fair Value Measurements - Fair Value of Contingent Consideration Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	$ 0.0	$ (209.1)	$ (50.7)
Fair value, measurements, recurring
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of year	$ 0.0	209.1
Fair value, end of year		$ 0.0	$ 209.1

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes


Note 17:			Income Taxes

Income Tax Expense

Income before income tax (benefit) expense and the income tax (benefit) expense consist of the following:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Income before income tax (benefit) expense:
Domestic	$	192.4	$	1,842.0	$	448.3
Foreign	1,104.4		1,749.8		1,296.9
Total income before income tax (benefit) expense	$	1,296.8	$	3,591.8	$	1,745.2
Income tax (benefit) expense:
Current:
Federal	$	377.6	$	694.5	$	319.1
State	15.1		39.0		23.1
Foreign	48.4		67.9		137.1
Total current	441.1		801.4		479.3
Deferred:
Federal	(587.4)		(328.3)		(242.5)
State	(12.7)		2.5		(11.9)
Foreign	294.3		157.2		(172.4)
Total deferred	(305.8)		(168.6)		(426.8)
Total income tax (benefit) expense	$	135.3	$	632.8	$	52.5

Transition Toll Tax

The Tax Cuts and Jobs Act of 2017 eliminated the deferral of U.S. income tax on the historical unrepatriated earnings by imposing the one-time mandatory deemed repatriation tax on accumulated foreign subsidiaries' previously untaxed foreign earnings. The Transition Toll Tax was assessed on our share of our foreign corporations' accumulated foreign earnings that were not previously taxed. Earnings in the form of cash and cash equivalents were taxed at a rate of 15.5% and all other earnings were taxed at a rate of 8.0%.

As of December 31, 2023 and 2022, we have accrued income tax liabilities of $419.5 million and $558.0 million, respectively, under the Transition Toll Tax. Of the amounts accrued as of December 31, 2023, approximately $185.4 million is expected to be paid within one year. The Transition Toll Tax is being paid in installments over an eight--year period, which started in 2018, and will not accrue interest.

Unremitted Earnings

At December 31, 2023, we considered our earnings not to be permanently reinvested outside the U.S. and therefore recorded deferred tax liabilities associated with an estimate of the total withholding taxes expected as a result of our repatriation of earnings. Other than for earnings, we are permanently reinvested for book/tax basis differences of approximately $1.5 billion as of December 31, 2023, primarily arising through the impacts of purchase accounting. These permanently reinvested basis differences could reverse through sales of the foreign subsidiaries, as well as various other events, none of which were considered probable as of December 31, 2023. The residual U.S. tax liability, if these differences reverse, would be between $300.0 million and $400.0 million as of December 31, 2023.

Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Deferred tax assets:
Tax credits	$	252.8	$	112.6
Inventory, other reserves and accruals	203.7		202.8
Intangibles, net	1,153.9		1,370.3
Neurimmune's tax basis in ADUHELM	—		470.3
IRC Section 174 capitalized research and development	570.8		271.8
Net operating loss	1,700.4		1,845.9
Share-based compensation	36.1		37.2
Other	293.3		280.7
Valuation allowance	(1,278.7)		(2,003.3)
Total deferred tax assets	$	2,932.3	$	2,588.3
Deferred tax liabilities:
Purchased inventory valuation step-up and intangible assets	$	(1,257.4)	$	(76.1)
Samsung Bioepis investment installments	(35.5)		(138.0)
GILTI	(1,136.9)		(1,002.0)
Tax credits	—		(228.7)
Depreciation, amortization and other	(215.7)		(251.8)
Total deferred tax liabilities	$	(2,645.5)	$	(1,696.6)

As of December 31, 2023, 2022, 2021 and 2020, we had a valuation allowance of $1,278.7 million, $2,003.3 million, $1,961.3 million and $1,753.9 million, respectively, related to net operating losses in Switzerland and Neurimmune's tax basis in ADUHELM. The change in the valuation allowance between December 31, 2023 and 2022, was primarily driven by a reduction of approximately $470.3 million related to the elimination of Neurimmune's tax basis in ADUHELM as a result of its deconsolidation and reduction of approximately $230.3 million due to movements in net operating loss deferred tax assets in Switzerland. The net income tax impact of the changes in the valuation allowance was an expense of approximately $7.4 million for the year ended December 31, 2023. The change in the valuation allowance between December 31, 2022 and 2021, and between December 31, 2021 and 2020, was primarily driven by additions of $85.0 million and $390.0 million, respectively, related to Neurimmune's tax basis in ADUHELM. For additional information on the deconsolidation and our collaboration arrangement with Neurimmune, please read Note 20, Investments in Variable Interest Entities, to these consolidated financial statements.

In addition to deferred tax assets and liabilities, we have recorded deferred charges related to intra-entity sales of inventory. As of December 31, 2023 and 2022, the total deferred charges were $69.3 million and $56.6 million, respectively.

Inflation Reduction Act

In August 2022 the IRA was signed into law in the U.S. The IRA introduced new tax provisions, including a 15.0% corporate alternative minimum tax and a 1.0% excise tax on stock repurchases. The provisions of the IRA are effective for periods after December 31, 2022. The IRA did not result in any material adjustments to our income tax provision or income tax balances as of December 31, 2023 and 2022. Preliminary guidance has been issued by the IRS and we expect additional guidance and regulations to be issued in future periods. We will continue to assess its potential impact on our business and results of operations as further information becomes available.

Tax Rate

A reconciliation between the U.S. federal statutory tax rate and our effective tax rate is summarized as follows:


	For the Years Ended December 31,
	2023		2022		2021
Statutory rate	21.0	%	21.0	%	21.0	%
State taxes	1.1		1.1		0.8
Taxes on foreign earnings	(5.9)		(4.9)		(10.5)
Tax credits	(7.3)		(1.7)		(3.8)
Purchased inventory valuation step-up and intangible assets	0.7		0.3		(1.6)

GILTI	(0.6)		0.7		1.3
Sale of Samsung Bioepis	—		(1.6)		—
Litigation settlement agreement	—		2.6		—

Neurimmune tax impacts	—		2.3		(5.3)
Internal reorganization	(0.1)		(1.4)		—
Other, including permanent items	1.5		(0.8)		1.1
Effective tax rate	10.4	%	17.6	%	3.0	%

Changes in Tax Rate

For the year ended December 31, 2023, compared to 2022, the decrease in our effective tax rate was driven by the impact of the non-cash changes in the value of our equity investments, the impact of Fit for Growth related expenses and Reata acquisition-related expenses, as well as the combined net unfavorable tax rate impacts in 2022 related to a litigation settlement agreement, the sale of our equity interest in Samsung Bioepis, the impact of a Neurimmune valuation allowance, as discussed below, and an international reorganization to align with global tax developments. The change also benefits from the resolution of an uncertain tax matter during the first quarter of 2023 related to tax credits.

For the year ended December 31, 2022, compared to 2021, the increase in our effective tax rate, excluding the impact of the net Neurimmune deferred tax asset, as discussed below, includes the tax impacts of the litigation settlement agreement and the sale of our building at 125 Broadway. These increases were partially offset by the impact of the current year tax benefits related to an international reorganization to align with global tax developments, the impacts of the sale of our equity interest in Samsung Bioepis and the tax impacts of the decision to discontinue development of vixotrigine. Further in 2021, our effective tax rate benefited from the tax effects of the BIIB111 and BIIB112 impairment charges and the non-cash tax effects of changes in the value of our equity instruments.

For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

For additional information on the litigation settlement agreement, please read Note 18, Other Consolidated Financial Statement Detail, to these consolidated financial statements.

Neurimmune Deferred Tax Asset

During the first quarter of 2022, upon issuance of the final NCD related to ADUHELM, we recorded an increase in a valuation allowance of approximately $85.0 million to reduce the net value of this deferred tax asset to zero.

These adjustments to our net deferred tax asset were each recorded with an equal and offsetting amount assigned to net income (loss) attributable to noncontrolling interests, net of tax in our consolidated statements of income, resulting in a zero net impact to net income attributable to Biogen Inc.

During the fourth quarter of 2023 Neurimmune was deconsolidated from our consolidated financial statements. For additional information on the deconsolidation and our collaboration arrangement with Neurimmune, please read Note 20, Investments in Variable Interest Entities, to these consolidated financial statements.

Tax Attributes

As of December 31, 2023, we had general business credit carry forwards for U.S. federal income tax purposes of approximately $141.8 million that begin to expire in 2030 and net operating losses of approximately $913.1 million that do not expire. For U.S. state income tax purposes, we had research and investment credit carry forwards of approximately $140.5 million that begin to expire in 2027 and net operating losses of approximately $21.0 million that begin to expire in 2036. For foreign income tax purposes, we had $13.0 billion of federal net operating loss carryforwards that begin to expire in 2027 and $12.2 billion of Swiss cantonal net operating loss carryforwards that begin to expire in 2027.

In assessing the realizability of our deferred tax assets, we have considered whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. In making this determination, under the applicable financial reporting standards, we are allowed to consider the scheduled reversal of deferred tax liabilities, projected future taxable income and tax planning strategies. Based upon the level of historical taxable income and income tax liability and projections for future taxable income over the periods in which the deferred tax assets are utilizable, we believe it is more likely than not that we will realize the net benefits of the deferred tax assets of our wholly owned subsidiaries, net of the recorded valuation allowance. In the event that actual results differ from our estimates or we adjust our estimates in future periods, we may need to adjust or establish a valuation allowance, which could materially impact our consolidated financial position and results of operations.

Accounting for Uncertainty in Income Taxes

A reconciliation of the beginning and ending amount of our unrecognized tax benefits is summarized as follows:



(In millions)	2023		2022		2021
Beginning balance	$	606.4	$	563.4	$	75.7
Additions based on tax positions related to the current period	5.2		36.3		4.2
Additions for tax positions of prior periods	60.2		23.4		509.9
Reductions for tax positions of prior periods	(485.0)		(14.9)		(18.8)
Statute expirations	(2.1)		(1.6)		(3.2)
Settlement refund (payment)	(11.3)		(0.2)		(4.4)
Ending balance	$	173.4	$	606.4	$	563.4

During the year ended December 31, 2021, we increased our gross unrecognized tax benefits by approximately $455.0 million, related to a deferred tax asset for Swiss tax purposes for Neurimmune's tax basis in ADUHELM. This unrecognized tax benefit was recorded as a reduction to the gross deferred tax asset, resulting in the net deferred tax asset, as discussed above, and not as a separate liability on our consolidated balance sheets. As of December 31, 2022, the unrecognized tax benefits related to Neurimmune was approximately $450.0 million. During the year ended December 31, 2023, we decreased our gross unrecognized tax benefits by approximately $450.0 million related to this item as a result of the deconsolidation of Neurimmune.

We file income tax returns in various U.S. states and in U.S. federal and other foreign jurisdictions. With few exceptions, we are no longer subject to U.S. federal tax examination for years before 2019 or state, local or non-U.S. income tax examinations for years before 2013.

The U.S. Internal Revenue Service and other national tax authorities routinely examine our intercompany transfer pricing with respect to intellectual property related transactions and it is possible that they may disagree with one or more positions we have taken with respect to such valuations.

Included in the balance of unrecognized tax benefits as of December 31, 2023, 2022 and 2021, are $147.6 million, $134.0 million and $87.5 million (net of the federal benefit on state issues), respectively, of unrecognized tax benefits that, if recognized, would affect the effective income tax rate in future periods.

We recognize potential interest and penalties related to unrecognized tax benefits in income tax expense. During the years ended December 31, 2023, 2022 and 2021, we recognized total interest and penalty expense of $5.1 million, $0.7 million and $2.7 million, respectively. We have accrued $30.2 million and $25.2 million for the payment of interest and penalties as of December 31, 2023 and 2022, respectively.

It is reasonably possible that we will adjust the value of our uncertain tax positions related to certain transfer pricing, collaboration matters, withholding taxes and other issues as we receive additional information from various taxing authorities, including reaching settlements with such authorities.

We estimate that it is reasonably possible that our gross unrecognized tax benefits, exclusive of interest, could decrease by up to approximately $20.0 million in the next 12 months as a result of various audit closures, settlements and expiration of the statute of limitations.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Collaborative and Other Relationships - Pretax Profit Sharing Formula (Details) - GAZYVA	Dec. 31, 2023	Apr. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Until Second GAZYVA Threshold Date	37.50%		37.50%	37.50%
After Second GAZYVA Threshold Date	35.00%	35.00%

Other Consolidated Financial Statement Detail - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interest	$ 252.2	$ 262.5	$ 280.8
Income taxes	$ 740.7	$ 932.9	$ 247.9

Derivative Instruments - Foreign Currency Forward Contracts Entered into Hedge Forecasted Revenues (Details) - Designated as Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts and options	$ 1,169.0	$ 1,715.5
Euro
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts and options	1,169.0	1,495.5
British pound
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts and options	0.0	162.8
Swiss franc
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts and options	0.0	0.0
Canadian dollar
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts and options	$ 0.0	$ 57.2

Collaborative and Other Relationships - Profit Sharing (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
RITUXAN
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of co promotion operating profits first fifty million	30.00%
Until Second GAZYVA Threshold Date	37.50%
GAZYVA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of co promotion operating profits first fifty million	35.00%
Co-promotion operating profit threshold for Rituxan in US and Canada to determine share of co promotion operating profit prior to amendment	$ 50.0	$ 50.0	$ 50.0
Limit of gross sale of GAZYVA to be achieved in preceding 12 months under option one	500.0
Limit of gross sale of GAZYVA to be achieved in any 12 months under option one	150.0
Sales trigger gross sales threshold	$ 350.0
Until Second GAZYVA Threshold Date	37.50%	37.50%	37.50%
New Anti Cd20
Collaborative arrangements and non-collaborative arrangement transactions
Future percentage of co-promotion operating profits		37.50%	37.50%

Collaborative and Other Relationships - Ionis (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended					12 Months Ended
	Dec. 31, 2019	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018
Collaborative arrangements and non-collaborative arrangement transactions
Cost of sales, excluding amortization and impairment of acquired intangible assets						$ 2,533.4	$ 2,278.3	$ 2,109.7
Research and development						2,462.0	2,231.1	2,501.2
Ionis Pharmaceuticals
Collaborative arrangements and non-collaborative arrangement transactions
Term of collaboration agreement		10 years		6 years
Total payment to enter collaboration agreement		$ 1,000.0
Upfront payment for collaboration agreement		$ 375.0
Investment in common stock, shares purchased (in shares)		11.5
Purchase of common stock		$ 625.0
Prepaid research and discovery services		50.9
Research and development		324.1				7.5	10.0	22.5
Estimated additional payments upon achievement of development and commercial milestones									$ 260.0
Upfront and milestone payments made to collaborative partner			$ 25.0
Expected additional milestone payments when certain sales threshold is met									$ 800.0
License fee				$ 70.0	$ 70.0
Expected license fee and regulatory milestone payments				$ 130.0	$ 130.0
Research and development expense asset acquired	$ 45.0
Additional milestone payment	155.0
Ionis Pharmaceuticals \| SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Cost of sales, excluding amortization and impairment of acquired intangible assets						240.2	243.1	267.1
Ionis Pharmaceuticals \| BIIB115
Collaborative arrangements and non-collaborative arrangement transactions
Upfront payment for collaboration agreement								60.0
Ionis Pharmaceuticals \| SOD1
Collaborative arrangements and non-collaborative arrangement transactions
Research and development							$ 17.0	$ 10.0
Estimated additional payments upon achievement of development and commercial milestones	55.0
Ionis Pharmaceuticals \| BIIB080
Collaborative arrangements and non-collaborative arrangement transactions
Research and development expense asset acquired	10.0
Ionis Pharmaceuticals \| QALSODY
Collaborative arrangements and non-collaborative arrangement transactions
Research and development						$ 16.0
Estimated additional payments upon achievement of development and commercial milestones	$ 20.0
Ionis Pharmaceuticals \| Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Estimated additional payments upon achievement of development and commercial milestones		125.0
Ionis Pharmaceuticals \| Minimum \| SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration						11.00%
Ionis Pharmaceuticals \| Minimum \| QALSODY
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration						11.00%
Ionis Pharmaceuticals \| Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Estimated additional payments upon achievement of development and commercial milestones		$ 270.0
Ionis Pharmaceuticals \| Maximum \| SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration						15.00%
Ionis Pharmaceuticals \| Maximum \| QALSODY
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration						15.00%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income before income tax provision and the income tax expense

Income before income tax (benefit) expense and the income tax (benefit) expense consist of the following:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Income before income tax (benefit) expense:
Domestic	$	192.4	$	1,842.0	$	448.3
Foreign	1,104.4		1,749.8		1,296.9
Total income before income tax (benefit) expense	$	1,296.8	$	3,591.8	$	1,745.2
Income tax (benefit) expense:
Current:
Federal	$	377.6	$	694.5	$	319.1
State	15.1		39.0		23.1
Foreign	48.4		67.9		137.1
Total current	441.1		801.4		479.3
Deferred:
Federal	(587.4)		(328.3)		(242.5)
State	(12.7)		2.5		(11.9)
Foreign	294.3		157.2		(172.4)
Total deferred	(305.8)		(168.6)		(426.8)
Total income tax (benefit) expense	$	135.3	$	632.8	$	52.5

Components of deferred tax assets and liabilities

Significant components of our deferred tax assets and liabilities are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Deferred tax assets:
Tax credits	$	252.8	$	112.6
Inventory, other reserves and accruals	203.7		202.8
Intangibles, net	1,153.9		1,370.3
Neurimmune's tax basis in ADUHELM	—		470.3
IRC Section 174 capitalized research and development	570.8		271.8
Net operating loss	1,700.4		1,845.9
Share-based compensation	36.1		37.2
Other	293.3		280.7
Valuation allowance	(1,278.7)		(2,003.3)
Total deferred tax assets	$	2,932.3	$	2,588.3
Deferred tax liabilities:
Purchased inventory valuation step-up and intangible assets	$	(1,257.4)	$	(76.1)
Samsung Bioepis investment installments	(35.5)		(138.0)
GILTI	(1,136.9)		(1,002.0)
Tax credits	—		(228.7)
Depreciation, amortization and other	(215.7)		(251.8)
Total deferred tax liabilities	$	(2,645.5)	$	(1,696.6)

Reconciliation between the U.S. federal statutory tax rate and effective tax rate

A reconciliation between the U.S. federal statutory tax rate and our effective tax rate is summarized as follows:


	For the Years Ended December 31,
	2023		2022		2021
Statutory rate	21.0	%	21.0	%	21.0	%
State taxes	1.1		1.1		0.8
Taxes on foreign earnings	(5.9)		(4.9)		(10.5)
Tax credits	(7.3)		(1.7)		(3.8)
Purchased inventory valuation step-up and intangible assets	0.7		0.3		(1.6)

GILTI	(0.6)		0.7		1.3
Sale of Samsung Bioepis	—		(1.6)		—
Litigation settlement agreement	—		2.6		—

Neurimmune tax impacts	—		2.3		(5.3)
Internal reorganization	(0.1)		(1.4)		—
Other, including permanent items	1.5		(0.8)		1.1
Effective tax rate	10.4	%	17.6	%	3.0	%

Reconciliation of beginning and ending amount of unrecognized tax benefits

A reconciliation of the beginning and ending amount of our unrecognized tax benefits is summarized as follows:



(In millions)	2023		2022		2021
Beginning balance	$	606.4	$	563.4	$	75.7
Additions based on tax positions related to the current period	5.2		36.3		4.2
Additions for tax positions of prior periods	60.2		23.4		509.9
Reductions for tax positions of prior periods	(485.0)		(14.9)		(18.8)
Statute expirations	(2.1)		(1.6)		(3.2)
Settlement refund (payment)	(11.3)		(0.2)		(4.4)
Ending balance	$	173.4	$	606.4	$	563.4

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of assets and liabilities recorded at fair value


	As of December 31, 2023
(In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	610.7	$	—	$	610.7	$	—




Marketable equity securities	416.8		416.8		—		—
Other current assets:
Receivable from Samsung BioLogics(1)	430.0		—		—		430.0
Derivative contracts	11.9		—		11.9		—
Other non-current assets:
Plan assets for deferred compensation	37.5		—		37.5		—

Total	$	1,506.9	$	416.8	$	660.1	$	430.0
Liabilities:
Derivative contracts	$	31.6	$	—	$	31.6	$	—

Total	$	31.6	$	—	$	31.6	$	—


	As of December 31, 2022
(In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	2,847.6	$	—	$	2,847.6	$	—
Marketable debt securities:
Corporate debt securities	1,231.6		—		1,231.6		—
Government securities	810.3		—		810.3		—
Mortgage and other asset backed securities	137.3		—		137.3		—
Marketable equity securities	791.1		791.1		—		—
Other current assets:
Receivable from Samsung BioLogics(1)	798.8		—		—		798.8
Other non-current assets:
Derivative contracts	63.0		—		63.0		—
Plan assets for deferred compensation	32.8		—		32.8		—
Receivable from Samsung BioLogics(1)	405.4		—		—		405.4
Total	$	7,117.9	$	791.1	$	5,122.6	$	1,204.2
Liabilities:
Derivative contracts	$	26.0	$	—	$	26.0	$	—

Total	$	26.0	$	—	$	26.0	$	—

Fair value of contingent consideration obligations

The following table provides a roll forward of the fair value of our contingent consideration obligations, which were classified as Level 3 measurements:


	As of December 31,
(In millions)	2022
Fair value, beginning of year	$	209.1
Changes in fair value	(209.1)

Fair value, end of year	$	—

Summary of fair and carrying value of debt instruments

The fair values of our debt instruments, which are Level 2 liabilities, are summarized as follows:


	Fair Value As of December 31,
(In millions)	2023		2022
Current portion:
2023 Term Loan 364-day tranche(1)	$	150.0	$	—
Current portion of notes payable and term loan	150.0		—

Non-current portion:
2023 Term Loan three-year tranche(1)	500.0		—
4.050% Senior Notes due September 15, 2025	1,721.5		1,699.9
2.250% Senior Notes due May 1, 2030	1,279.3		1,219.0
5.200% Senior Notes due September 15, 2045	1,089.7		1,033.2
3.150% Senior Notes due May 1, 2050	1,049.0		989.0
3.250% Senior Notes due February 15, 2051	498.2		469.1
Non-current portion of notes payable and term loan	6,137.7		5,410.2
Total notes payable and term loan	$	6,287.7	$	5,410.2

Litigation (Details) - USD ($) $ in Thousands		1 Months Ended
Litigation (Details) - USD ($) $ in Thousands	Sep. 26, 2023	Jan. 31, 2024	Oct. 31, 2023	Feb. 28, 2023	Jun. 30, 2023	Dec. 31, 2019
Loss Contingencies [Line Items]
Loss contingency					$ 49,900	$ 200,000
Bardoxolone Securities
Loss Contingencies [Line Items]
Payment made to Forward Pharma			$ 45,000
ERISA Class Action Litigaiton \| Subsequent Event
Loss Contingencies [Line Items]
Payment made to Forward Pharma		$ 9,750
Genentech
Loss Contingencies [Line Items]
Claims asserted				$ 88,300
Lender Dispute
Loss Contingencies [Line Items]
Claims asserted	$ 23,300

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Components of property, plant and equipment, net

We generally depreciate or amortize the cost of our property, plant and equipment using the straight-line method over the estimated useful lives of the respective assets, which are summarized as follows:


Asset Category			Useful Lives
Land			Not depreciated
Buildings			15 to 40 years
Leasehold Improvements			Lesser of the useful life or the term of the respective lease
Furniture and Fixtures			5 to 7 years
Machinery and Equipment			5 to 20 years
Computer Software and Hardware			3 to 5 years

Components of property, plant and equipment, net are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Land	$	202.4	$	202.4
Buildings	1,601.3		1,592.9
Leasehold improvements	135.7		107.7
Machinery and equipment	1,703.8		1,611.5
Computer software and hardware	1,032.1		999.9
Furniture and fixtures	61.5		61.1
Construction in progress	975.4		888.8
Total cost	5,712.2		5,464.3
Less: accumulated depreciation	(2,402.5)		(2,165.7)
Total property, plant and equipment, net	$	3,309.7	$	3,298.6

Leases - Schedule of Operating Leases (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Operating lease assets	Operating lease assets
Operating lease assets	$ 420.0	$ 403.9
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Operating lease liability, current	$ 90.3	$ 97.2
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term operating lease liabilities	Long-term operating lease liabilities
Long-term operating lease liabilities	$ 400.0	$ 333.0
Present value of operating lease liabilities	$ 490.3	$ 430.2

Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Share-based compensation expense included in consolidated statements of income

The following table summarizes share-based compensation expense included in our consolidated statements of income:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Research and development	$	296.7	$	98.5	$	89.3
Selling, general and administrative	371.7		175.1		169.5
Subtotal	668.4		273.6		258.8
Capitalized share-based compensation costs	(10.2)		(9.3)		(8.0)
Share-based compensation expense included in total cost and expense	658.2		264.3		250.8
Income tax effect	(132.6)		(49.2)		(46.7)
Share-based compensation expense included in net income attributable to Biogen Inc.	$	525.6	$	215.1	$	204.1

Summary of share-based compensation expense associated with each of our share-based compensating programs

The following table summarizes share-based compensation expense associated with each of our share-based compensation programs:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Market stock units	$	4.9	$	13.2	$	45.6
Time-vested restricted stock units	220.0		202.3		159.8
Performance stock units settled in stock	35.5		35.0		23.9
Performance stock units settled in cash	6.8		10.1		12.2
Employee stock purchase plan	10.5		12.7		17.3
Stock options	3.7		0.3		—
Reata equity awards(1)	387.0		—		—
Subtotal	668.4		273.6		258.8
Capitalized share-based compensation costs	(10.2)		(9.3)		(8.0)
Share-based compensation expense included in total cost and expense	$	658.2	$	264.3	$	250.8

(1) Relates to the Reata equity-based compensation expense attributable to the post-acquisition service period, associated with the accelerated vesting of stock options and RSUs previously granted to Reata employees that required no future services to vest. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

Schedule of Stock Options Roll Forward


	December 31, 2023
	Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at December 31, 2022	81,000	$	301.85	9.9 years
Granted	—	—
Exercised	—	—
Forfeited	—	—
Outstanding at December 31, 2023	81,000	$	301.85	8.9 years
Exercisable at December 31, 2023	27,000	$	301.85	8.9 years

Summary of market stock unit activity

The following table summarizes our MSU activity:


	December 31, 2023
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2022	113,000	$	366.52
Granted	—	—
Vested	(74,000)	368.87
Forfeited	(5,000)	372.87
Unvested at December 31, 2023	34,000	$	359.77

Assumptions used in valuation of market based stock units

The assumptions used in our valuation are summarized as follows:


												December 31, 2021
Expected dividend yield												—%
Range of expected stock price volatility												54.8% - 61.6%
Range of risk-free interest rates												0.06% - 0.21%
30 calendar day average stock price on grant date												$262.23 - $360.31
Weighted-average per share grant date fair value												$358.77

Performance stock units settled in stock activity

The following table summarizes our PSUs that settle in stock activity:


	December 31, 2023
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2022	336,000	$	292.95
Granted (1)	206,000	383.61
Vested	(100,000)	290.72
Forfeited	(53,000)	323.52
Unvested at December 31, 2023	389,000	$	325.73

(1) PSUs settled in stock granted in 2023 include awards granted in conjunction with our annual awards made in February 2023 and PSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant.

Performance stock units settled in cash activity

The assumptions used in our valuation are summarized as follows:


	For the Years Ended December 31,
	2023	2022
Expected dividend yield	—%	—%
Range of expected stock price volatility	44.7%	44.0% - 45.9%
Range of risk-free interest rates	4.1%	1.8% - 3.9%
30 calendar day average stock price on grant date	$283.93	$231.31 - $294.86
Weighted-average per share grant date fair value	$383.61	$294.43

The following table summarizes our PSUs that settle in cash activity:


			December 31, 2023
			Shares
Unvested at December 31, 2022			83,000
Granted(1)			5,000
Vested			(41,000)
Forfeited			(6,000)
Unvested at December 31, 2023			41,000

(1) PSUs settled in cash granted in 2023 represent the adjustment recorded to reflect the total number of units earned based on the finalization of the related performance multiplier for awards previously granted in 2020.

The fair values of PSUs settled in cash that vested in 2023, 2022 and 2021 totaled $11.7 million, $11.0 million and $9.9 million, respectively.

Time-vested restricted stock units activity

The following table summarizes our RSU activity:


	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2022	1,946,000	$	237.90
Granted (1)	1,171,000	282.92
Vested	(822,000)	249.12
Forfeited	(439,000)	257.66
Unvested at December 31, 2023	1,856,000	$	256.74

(1) RSUs granted in 2023 primarily represent RSUs granted in conjunction with our annual awards made in February 2023 and awards made in conjunction with the hiring of new employees. RSUs granted in 2023 also include approximately 7,300 RSUs granted to our Board of Directors.

Shares issued under employee stock purchase plan

The following table summarizes our ESPP activity:


	For the Years Ended December 31,
(In millions, except share amounts)	2023		2022		2021
Shares issued under the 2015 ESPP	199,000		241,000		248,000
Cash received under the 2015 ESPP	$	45.1	$	44.2	$	54.4

Other Consolidated Financial Statement Detail

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Other Consolidated Financial Statement Detail


Note 18:			Other Consolidated Financial Statement Detail

Supplemental Cash Flow Information

Supplemental disclosure of cash flow information for the years ended December 31, 2023, 2022 and 2021, is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Cash paid during the year for:
Interest	$	252.2	$	262.5	$	280.8
Income taxes	740.7		932.9		247.9

Other (Income) Expense, Net

Components of other (income) expense, net, are summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Gain on sale of equity interest in Samsung Bioepis(1)	$	—	$	(1,505.4)	$	—
Litigation settlement agreement and settlement fees	—		917.0		—
Interest income	(276.5)		(89.3)		(11.0)
Interest expense	246.9		246.6		253.6
(Gains) losses on investments, net	291.2		277.3		824.9
Foreign exchange (gains) losses, net	50.4		35.5		22.4
Other, net	3.5		10.1		5.6
Total other (income) expense, net	$	315.5	$	(108.2)	$	1,095.5

(1) Reflects the pre-tax gain, net of transaction costs, recognized from the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics in April 2022. For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

The (gains) losses on investments, net, as reflected in the table above, relate to debt securities, equity securities of certain biotechnology companies, venture capital funds where the underlying investments are in equity securities of certain biotechnology companies and non-marketable equity securities.

During the second quarter of 2022 we recorded a pre-tax charge of $900.0 million, plus settlement fees and expenses, related to a litigation settlement agreement to resolve a qui tam litigation relating to conduct prior to 2015. This charge is included within other (income) expense, net in our consolidated statements of income for the year ended December 31, 2022.

The following table summarizes our (gains) losses on investments, net that relates to our equity securities held as of December 31, 2023, 2022 and 2021:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Net (gains) losses recognized on equity securities	$	275.2	$	264.7	$	821.1
Less: Net (gains) losses realized on equity securities	5.2		—		(10.3)
Net unrealized (gains) losses recognized on equity securities	$	270.0	$	264.7	$	831.4

The net unrealized losses recognized during the year ended December 31, 2023, primarily reflect a decrease in the aggregate fair value of our investments in Sage, Denali, Sangamo and Ionis common stock of approximately $248.5 million.

The net unrealized losses recognized during the year ended December 31, 2022, primarily reflect a decrease in the aggregate fair value of our investments in Denali and Sangamo common stock of approximately $278.0 million, partially offset by an increase in the fair value of Ionis and Sage common stock of approximately $27.3 million.

Accrued Expense and Other

Accrued expense and other consists of the following:


	As of December 31,
(In millions)	2023		2022

Revenue-related reserves for discounts and allowances	$	926.5	$	891.6
Employee compensation and benefits	335.1		395.6
Collaboration expense	214.6		277.9
Royalties and licensing fees	191.5		209.4



Reata acquisition-related accrued expense	117.5		—
Other	838.4		746.9
Total accrued expense and other	$	2,623.6	$	2,521.4

Other long-term liabilities were $781.1 million and $944.2 million as of December 31, 2023 and 2022, respectively, and included accrued income taxes totaling $403.2 million and $541.7 million, respectively.

Fair Value Measurements - Summary of Fair and Carrying Value of Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 26, 2023	Dec. 31, 2022	Feb. 28, 2021	Apr. 30, 2020
Debt Instrument
Interest rate on senior notes	3.625%
Long-term debt, gross	$ 7,217.3
Senior Notes
Debt Instrument
Notes payable, fair value	6,287.7		$ 5,410.2
2023 Term Loan 364-day tranche \| Senior Notes
Debt Instrument
Notes payable, fair value	150.0		0.0
Current portion of notes payable and term loan \| Senior Notes
Debt Instrument
Notes payable, fair value	150.0		0.0
2023 Term loan three-year tranche \| Senior Notes
Debt Instrument
Notes payable, fair value	500.0		0.0
4.050% Senior Notes due September 15, 2025 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,721.5		1,699.9
Interest rate on senior notes	4.05%
2.250% Senior Notes due May 1, 2030 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,279.3		1,219.0
Interest rate on senior notes	2.25%				2.25%
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,089.7		1,033.2
Interest rate on senior notes	5.20%			5.20%
3.150% Senior Notes due May 1, 2050 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,049.0		989.0
Interest rate on senior notes	3.15%				3.15%
3.250% Senior Notes due February 15, 2051 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 498.2		469.1
Interest rate on senior notes	3.25%			3.25%
Non-current portion of notes payable and term loan \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 6,137.7		$ 5,410.2
The Credit Facility \| Line of Credit \| Reata Pharmaceuticals, Inc \| Secured Debt
Debt Instrument
Long-term debt, gross		$ 1,000.0

Equity (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Summary of common stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2023, 2022 and 2021:

As of December 31, 2023

As of December 31, 2022

As of December 31, 2021

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

168.7

144.9

1,000.0

167.9

144.0

1,000.0

170.8

147.0

Schedule of Accumulated Other Comprehensive Income (Loss)

The following tables summarize the changes in AOCI, net of tax by component:


	December 31, 2023
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2022	$	(15.7)	$	15.1	$	(1.1)	$	(163.2)	$	(164.9)
Other comprehensive income (loss) before reclassifications	2.3		(26.8)		(1.5)		37.1		11.1
Amounts reclassified from AOCI	13.4		(13.3)		—		—		0.1
Net current period other comprehensive income (loss)	15.7		(40.1)		(1.5)		37.1		11.2
Balance, December 31, 2023	$	—	$	(25.0)	$	(2.6)	$	(126.1)	$	(153.7)


	December 31, 2022
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Gains (Losses) on Net Investment Hedges, Net of Tax(1)		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2021	$	(2.2)	$	53.8	$	25.5	$	(44.8)	$	(139.0)	$	(106.7)
Other comprehensive income (loss) before reclassifications	(23.5)		137.3		12.6		43.7		(83.1)		87.0
Amounts reclassified from AOCI	10.0		(176.0)		(38.1)		—		58.9		(145.2)
Net current period other comprehensive income (loss)	(13.5)		(38.7)		(25.5)		43.7		(24.2)		(58.2)
Balance, December 31, 2022	$	(15.7)	$	15.1	$	—	$	(1.1)	$	(163.2)	$	(164.9)


	December 31, 2021
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Gains (Losses) on Net Investment Hedges, Net of Tax		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2020	$	1.4	$	(179.0)	$	(8.5)	$	(66.3)	$	(46.6)	$	(299.0)
Other comprehensive income (loss) before reclassifications	(6.6)		178.2		33.4		21.5		(92.4)		134.1
Amounts reclassified from AOCI	3.0		54.6		0.6		—		—		58.2
Net current period other comprehensive income (loss)	(3.6)		232.8		34.0		21.5		(92.4)		192.3
Balance, December 31, 2021	$	(2.2)	$	53.8	$	25.5	$	(44.8)	$	(139.0)	$	(106.7)

Reclassification out of Accumulated Other Comprehensive Income

The following table summarizes the amounts reclassified from AOCI:


(In millions)	Amounts Reclassified from AOCI						Income Statement Location
	For the Years Ended December 31,
	2023		2022		2021
Gains (losses) on securities available for sale	$	(17.0)	$	(12.6)	$	(3.8)	Other (income) expense
	3.6		2.6		0.8		Income tax (benefit) expense

Gains (losses) on cash flow hedges	11.6		201.6		(60.0)		Revenue
	3.7		(5.5)		(0.8)		Operating expense
	(0.3)		(0.3)		0.2		Other (income) expense
	(1.7)		(19.8)		6.0		Income tax (benefit) expense

Gains (losses) on net investment hedges(1)	—		38.1		(0.6)		Other (income) expense

Currency translation adjustments	—		(58.9)		—		Other (income) expense

Total reclassifications, net of tax	$	(0.1)	$	145.2	$	(58.2)

Fair Value Measurements - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
Fair Value Measurements - Narrative (Details) - USD ($)	Feb. 28, 2015	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2022
Business Acquisition, Contingent Consideration [Line Items]
Impairment of assets			$ 0	$ 0
Convergence Pharmaceuticals
Business Acquisition, Contingent Consideration [Line Items]
Additions	$ 274,500,000		0
Contingent consideration obligations					$ 209,100,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				209,100,000
BIIB111
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets				365,000,000
BIIB111 \| In-process research and development
Business Acquisition, Contingent Consideration [Line Items]
Intangible asset, fair value			0			$ 0
BIIB111 \| Nightstar
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets					365,000,000
BIIB112
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets					$ 220,000,000
BIIB112 \| In-process research and development
Business Acquisition, Contingent Consideration [Line Items]
Intangible asset, fair value			$ 0			$ 0
BIIB112 \| Nightstar
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets				220,000,000
BIIB054
Business Acquisition, Contingent Consideration [Line Items]
Reduction in contingent consideration				195,400,000
TGN \| In-process research and development
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets		$ 44,300,000		$ 119,600,000

Earnings per Share - Narrative (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock, at cost (in shares)	0
2020 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock, at cost (in shares)		3,600	6,000

Indebtedness - Summary of Indebtedness (Details) - USD ($) $ in Millions	Sep. 26, 2023	Dec. 31, 2023	Dec. 31, 2022	Feb. 28, 2021	Apr. 30, 2020
Non-current portion:
Non-current portion of notes payable and term loan		$ 6,788.2	$ 6,281.0
Interest rate on senior notes		3.625%
Senior Notes
Non-current portion:
Non-current portion of notes payable and term loan		$ 6,788.2	6,281.0
Line of Credit
Current portion:
Current portion of notes payable and term loan		150.0	0.0
2023 Term Loan \| Line of Credit
Current portion:
Current portion of notes payable and term loan		150.0	0.0
Non-current portion:
Non-current portion of notes payable and term loan		500.0	0.0
2023 Term Loan \| Line of Credit \| Reata Pharmaceuticals, Inc
Non-current portion:
Proceeds from long-term lines of credit	$ 1,000.0
2023 Term Loan \| Line of Credit \| Reata Pharmaceuticals, Inc \| 2023 Term Loan 364-day tranche
Non-current portion:
Proceeds from long-term lines of credit	500.0
2023 Term Loan \| Line of Credit \| Reata Pharmaceuticals, Inc \| 2023 Term loan three-year tranche
Non-current portion:
Proceeds from long-term lines of credit	$ 500.0
4.050% Senior Notes due September 15, 2025 \| Senior Notes
Non-current portion:
Non-current portion of notes payable and term loan		$ 1,746.6	1,744.7
Interest rate on senior notes		4.05%
2.250% Senior Notes due May 1, 2030 \| Senior Notes
Non-current portion:
Non-current portion of notes payable and term loan		$ 1,493.8	1,492.9
Interest rate on senior notes		2.25%			2.25%
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Non-current portion:
Non-current portion of notes payable and term loan		$ 1,100.7	1,100.3
Interest rate on senior notes		5.20%		5.20%
3.150% Senior Notes due May 1, 2050 \| Senior Notes
Non-current portion:
Non-current portion of notes payable and term loan		$ 1,474.3	1,473.8
Interest rate on senior notes		3.15%			3.15%
3.250% Senior Notes due February 15, 2051 \| Senior Notes
Non-current portion:
Non-current portion of notes payable and term loan		$ 472.8	$ 469.3
Interest rate on senior notes		3.25%		3.25%

Litigation

12 Months Ended

Dec. 31, 2023

Loss Contingency, Information about Litigation Matters [Abstract]

Litigation


Note 21:			Litigation

We are currently involved in various claims, investigations and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies, to these consolidated financial statements.

With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties’ legal theories; and (v) the parties' settlement positions. If an estimate of the possible loss or range of loss can be made at this time, it is included in the potential loss contingency description below.

The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third-parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated results of operations and financial position: (i) loss of patent protection; (ii) inability to continue to engage in certain activities; and (iii) payment of significant damages, royalties, penalties and/or license fees to third parties.

Loss Contingencies

ADUHELM Securities Litigation

We and certain current and former officers are defendants in two actions related to ADUHELM filed in the United States District Court for the District of Massachusetts (the District Court). Both actions allege violations of federal securities laws under 15 U.S.C. §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5 and seek declarations of the actions as class actions and monetary relief. In October 2023 the United States Court of Appeals for the First Circuit reversed in part and affirmed in part the dismissal of the shareholder action related to ADUHELM that was filed in November 2020. In March 2023 the District Court dismissed the shareholder action that was filed in February 2022. In May 2023 the plaintiff filed a motion to alter the judgment and amend the complaint, which is pending.

Derivative Actions

We and members of the Board of Directors are named as defendants in derivative actions filed by shareholders in February and July 2022, in the U.S. District Court for the District of Massachusetts. The actions allege violations of federal securities laws under 15 U.S.C. §78n(a) and 17 C.F.R. §240 14.a-9, and breaches of fiduciary duties and waste of corporate assets, and seek declaratory and injunctive relief, monetary relief payable to Biogen, and attorneys’ fees and costs payable to the plaintiffs. The Court has stayed both cases.

IMRALDI Patent Litigation

In June 2022 Fresenius Kabi Deutschland GmbH (Fresenius Kabi) filed a claim for damages and injunctive relief against Biogen France SAS in the Tribunal de Grande Instance de Paris, alleging that IMRALDI, the adalimumab biosimilar product of Samsung Bioepis that Biogen commercializes in Europe, infringes the French counterpart of European Patent 3 145 488 (the EP ‘488 Patent), which expires in May 2035. In August 2022 Fresenius Kabi filed a claim for damages and injunctive relief against Biogen GmbH in the Düsseldorf Regional Court, alleging infringement of the German counterpart of the EP '488 Patent. A hearing in the Düsseldorf Regional Court was held in December 2023 and a decision is pending. The EP '488 Patent is the subject of opposition proceedings in the EPO Technical Boards of Appeal.

Litigation with Former Convergence Shareholders

In 2015 Biogen acquired Convergence, a U.K. company. In 2019 Shareholder Representative Services LLC, on behalf of the former shareholders of Convergence, asserted claims of $200.0 million for alleged breaches of the contract pursuant to which we acquired Convergence. In June 2023 Shareholder Representative Services LLC and 24 former shareholders filed suit against us in the High Court of Justice of England and Wales on one of the previously asserted claims, seeking payment of $49.9 million, interest and costs.

ERISA Class Action Litigation

In 2020 participants in the Biogen 401(k) Savings Plan filed actions against us in the U.S. District Court for the District of Massachusetts alleging breach of fiduciary duty under ERISA and seeking a declaration of the actions as class actions and monetary and other relief. In January 2024 the Court granted final approval of a settlement under which we agreed to pay $9.75 million without any admission of liability and dismissed the actions with prejudice.

Humana Patient Assistance Litigation

In March 2023 the U.S. District Court for the District of Massachusetts dismissed the previously disclosed action filed against us by Humana in September 2020. Humana had alleged damages related to our providing MS patients with free medications and making charitable contributions to non-profit organizations that assist MS patients and had alleged violations of the federal RICO Act and state laws. In December 2023 Humana appealed to the United States Court of Appeals for the First Circuit and the appeal is pending.

Genentech Litigation

In February 2023 Genentech, Inc. filed suit against us in the U.S. District Court for the Northern District of California, alleging that it is owed royalties on sales of TYSABRI that occurred after the expiration of a patent licensed by Genentech to Biogen, together with interest and costs. The Company estimates that the royalties claimed total approximately $88.3 million.

Bardoxolone Securities Litigation

In 2021 and 2022 putative stockholders of Reata (later acquired by Biogen) filed litigation in the United States District Court for the Eastern District of Texas alleging violations of the federal securities laws by Reata, certain former officers and directors and certain underwriters under 15 U.S.C. §78j(b) and §78t(a), 17 C.F.R. §240.10b-5, and 15 U.S.C. §§77k, 77l(a)(2) and 77o in connection with Reata's asset bardoxolone. Plaintiffs seek declaration of the actions as a class actions and monetary relief. In October 2023 the parties reached a settlement providing for payment by Reata of $45.0 million without any admission of liability. The Court preliminarily approved the settlement in November 2023 and has set a final fairness hearing for March 2024. We expect a portion of the payment to be reimbursed under Reata's insurance coverage.

Lender Dispute

One of Reata's lenders claims that approximately $23.3 million is owing under a loan agreement with Reata.

Other Matters

Government Investigations

The Company has received subpoenas from the SEC seeking information relating to ADUHELM and its launch. The Company has received a subpoena from the DOJ seeking information relating to our business operations in several foreign countries. The Company is also providing information relating to our business operations in several foreign countries to the SEC.

TYSABRI Biosimilar Patent Matter

In September 2022 we filed an action in the U.S. District Court for the District of Delaware against Sandoz Inc., other Sandoz entities and Polpharma Biologics S.A. under the Biologics Price Competition and Innovation Act, 42 U.S.C. §262, seeking a declaratory judgment of patent infringement.

Annulment Proceedings in the General Court of the European Union relating to TECFIDERA

In November 2020 Mylan Ireland filed an action in the General Court of the European Union to annul the EMA's decision not to validate its applications to market generic versions of TECFIDERA on the grounds that TECFIDERA benefits from regulatory data protection.

Hatch-Waxman Act Litigation relating to VUMERITY Orange-Book Listed Patents

In July 2023 Biogen and Alkermes Pharma Ireland Limited filed patent infringement proceedings relating to VUMERITY Orange-Book listed patents (U.S. Patent Nos. 8,669,281, 9,090,558 and 10,080,733) pursuant to the Drug Price Competition and Patent Term Restoration Act of 1984 (the Hatch-Waxman Act) in the U.S. District Court for the District of Delaware against Zydus Worldwide DMCC.

Product Liability and Other Legal Proceedings

We are also involved in product liability claims and other legal proceedings generally incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial condition.

Commitments and Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2024	Jun. 30, 2022
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		$ 5,100.0	$ 5,100.0
Accrued expenses		47.2	47.2
Cancellable future commitments		669.0	669.0
Liabilities associated with uncertain tax positions		172.0	172.0
Income taxes paid			185.4
2017 Tax Act
Business Acquisition [Line Items]
Transition toll tax liabilities		419.5	419.5	$ 558.0
Development Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		900.0	900.0
Regulatory Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		400.0	400.0
Commercial Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		3,800.0	$ 3,800.0
Maximum \| ADUHELM
Business Acquisition [Line Items]
Research and development expense asset acquired				$ 335.0
Ionis Pharmaceuticals
Business Acquisition [Line Items]
Research and development expense asset acquired	$ 45.0
Ionis Pharmaceuticals \| Minimum \| SPINRAZA
Business Acquisition [Line Items]
Percentage of royalties as per collaboration			11.00%
Ionis Pharmaceuticals \| Minimum \| QALSODY
Business Acquisition [Line Items]
Percentage of royalties as per collaboration			11.00%
Ionis Pharmaceuticals \| Maximum \| SPINRAZA
Business Acquisition [Line Items]
Percentage of royalties as per collaboration			15.00%
Ionis Pharmaceuticals \| Maximum \| QALSODY
Business Acquisition [Line Items]
Percentage of royalties as per collaboration			15.00%
Alkermes \| VUMERITY
Business Acquisition [Line Items]
Percentage of royalties as per collaboration			15.00%
Royalties payable period, post FDA approval			5 years
Aducanumab \| Forecast
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately					$ 109.0
Eisai \| ADUHELM \| Regulatory Milestones \| Neurimmune
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately						$ 100.0
Sage Therapeutics
Business Acquisition [Line Items]
Research and development expense asset acquired		$ 75.0
TYSABRI
Business Acquisition [Line Items]
Future contingent payment for annual worldwide net sales up to threshold, percentage		18.00%	18.00%
Future contingent payment threshold		$ 2,000.0	$ 2,000.0
Future contingent payment for annual worldwide net sales that exceeding threshold, percentage		25.00%	25.00%

Restructuring, Business Transformation and Other Cost Saving Initiatives - Fit for Growth Initiative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 218.8	$ 131.1	$ 0.0
2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	153.4
Accelerated Depreciation and Other Costs	59.1
Restructuring charges	212.5
Selling, general and administrative \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	0.0
Accelerated Depreciation and Other Costs	23.3
Restructuring charges	23.3
Research and development \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	0.0
Accelerated Depreciation and Other Costs	1.2
Restructuring charges	1.2
Restructuring charges \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	153.4
Accelerated Depreciation and Other Costs	34.6
Restructuring charges	$ 188.0

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Financial Instruments - Proceeds from Marketable Debt Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investments, All Other Investments [Abstract]
Proceeds from maturities and sales	$ 7,380.8	$ 3,671.0	$ 3,405.4
Realized gains	1.4	0.0	0.2
Realized losses	$ 18.4	$ 12.6	$ 4.0

Financial Instruments - Summary of Contractual Maturities (Details) $ in Millions	Dec. 31, 2022 USD ($)
Estimated Fair Value
Due in one year or less	$ 1,473.5
Due after one year through five years	694.4
Due after five years	11.3
Total marketable debt securities	2,179.2
Amortized Cost
Due in one year or less	1,483.3
Due after one year through five years	703.7
Due after five years	12.1
Amortized Cost	$ 2,199.1

Derivative Instruments - Summary of Unrealized Gain (Loss) on Derivative Instruments Included in AOCI (Details) - Foreign Exchange Forward - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains	$ 0.0	$ 29.9	$ 60.8
Unrealized (losses)	(34.8)	(21.3)	(7.0)
Net unrealized gains (losses)	$ (34.8)	$ 8.6	$ 53.8

- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References + Details

Segment Information

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Segment Information


Note 25:			Segment Information

We operate as one operating segment, focused on discovering, developing and delivering worldwide innovative therapies for people living with serious neurological and neurodegenerative diseases as well as related therapeutic adjacencies. Our CEO, as the CODM, manages and allocates resources to the operations of our company on a total company basis. Our research and development organization is responsible for the research and discovery of new product candidates and supports development and registration efforts for potential future products. Our pharmaceutical, operations and technology organization manages the development of the manufacturing processes, clinical trial supply, commercial product supply, distribution, buildings and facilities. Our commercial organization is responsible for U.S. and international development of our commercial products. The company is also supported by corporate staff functions. Managing and allocating resources on a total company basis enables our CEO to assess the overall level of resources available and how to best deploy these resources across functions, therapeutic areas and research and development projects that are in line with our long-term company-wide strategic goals. Consistent with this decision-making process, our CEO uses consolidated, single-segment financial information for purposes of evaluating performance, forecasting future period financial results, allocating resources and setting incentive targets.

Enterprise-wide disclosures about product revenue, other revenue and long-lived assets by geographic area are presented below. Revenue is primarily attributed to individual countries based on location of the customer or licensee.

Geographic Information

The following tables contain certain financial information by geographic area:


	December 31, 2023
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	3,141.4	$	2,127.4	$	868.0	$	649.4	$	460.5	$	7,246.7
Revenue from anti-CD20 therapeutic programs	1,618.5		0.4		—		—		70.7		1,689.6
Contract manufacturing, royalty and other revenue	673.6		11.7		—		214.0		—		899.3
Long-lived assets	1,443.0		2,248.0		17.5		8.3		12.9		3,729.7

	December 31, 2022
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	3,469.3	$	2,401.3	$	926.2	$	672.1	$	518.9	$	7,987.8
Revenue from anti-CD20 therapeutic programs	1,636.4		0.1		—		—		64.0		1,700.5
Contract manufacturing, royalty and other revenue	425.8		11.7		—		47.6		—		485.1
Long-lived assets	1,369.4		2,275.8		21.0		13.7		22.6		3,702.5

	December 31, 2021
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	3,805.7	$	2,626.0	$	1,162.4	$	688.0	$	564.8	$	8,846.9
Revenue from anti-CD20 therapeutic programs	1,596.7		—		—		—		61.8		1,658.5
Contract manufacturing, royalty and other revenue	429.9		9.7		—		36.7		—		476.3
Long-lived assets	1,390.5		2,337.8		25.4		16.4		21.7		3,791.8

(1) Represents amounts related to Europe less those attributable to Germany.

Long-Lived Assets

As of December 31, 2023, 2022 and 2021, approximately $2,156.4 million, $2,198.5 million and $2,237.0 million, respectively, of our long-lived assets were related to the construction of our large-scale biologics manufacturing facility in Solothurn, Switzerland.

For additional information on our Solothurn manufacturing facility, please read Note 11, Property, Plant and Equipment, to these consolidated financial statements.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-34

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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+ Details

Collaborative and Other Relationships

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborative and Other Relationships


Note 19:			Collaborative and Other Relationships

In connection with our business strategy, we have entered into various collaboration agreements that provide us with rights to develop, produce and market products using certain know-how, technology and patent rights maintained by our collaborative partners. Terms of the various collaboration agreements may require us to make milestone payments upon the achievement of certain product research and development objectives and pay royalties on future sales, if any, of commercial products resulting from the collaboration.

Depending on the collaborative arrangement, we may record funding receivable or payable balances with our collaboration partners, based on the nature of the cost-sharing mechanism and activity within the collaboration. Our significant collaborative arrangements are discussed below.

Genentech, Inc. (Roche Group)

We have certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, CLL and other conditions; RITUXAN HYCELA for the treatment of non-Hodgkin's lymphoma and CLL; GAZYVA for the treatment of CLL and follicular lymphoma; OCREVUS for the treatment of PPMS and RMS; LUNSUMIO for the treatment of relapsed or refractory follicular lymphoma; COLUMVI, a bispecific antibody for the treatment of non-Hodgkin's lymphoma, which was granted accelerated approval by the FDA during the second quarter of 2023; and have the option to add other potential anti-CD20 therapies, pursuant to our collaboration arrangements with Genentech, a wholly-owned member of the Roche Group. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.

If we undergo a change in control, as defined in our collaboration agreement, Genentech has the right to present an offer to buy the rights to RITUXAN and we must either accept Genentech’s offer or purchase Genentech’s rights on the same terms as its offer. Genentech will also be deemed concurrently to have purchased our rights to the remaining products in the collaboration on the terms set forth below.

Our collaboration with Genentech was created through a contractual arrangement and not through a joint venture or other legal entity.

RITUXAN

Genentech and its affiliates are responsible for the worldwide manufacture of RITUXAN as well as all development and commercialization activities as follows:

•U.S.: We have co-exclusively licensed our rights to develop, commercialize and market RITUXAN in the U.S.

•Canada: We have co-exclusively licensed our rights to develop, commercialize and market RITUXAN in Canada.

GAZYVA

The Roche Group and its sub-licensees maintain sole responsibility for the development, manufacture and commercialization of GAZYVA in the U.S. The level of gross sales of GAZYVA in the U.S. has impacted our percentage of the co-promotion profits for RITUXAN and LUNSUMIO, as summarized in the table below.

If we undergo a change in control, as defined in our collaboration agreement, Genentech will be deemed to have purchased our rights to GAZYVA in exchange for the continued payment of the current compensation payable for GAZYVA under the collaboration arrangement until the 11 year anniversary of the first commercial sale of GAZYVA in the U.S.

OCREVUS

Pursuant to the terms of our collaboration arrangements with Genentech, we receive a tiered royalty on U.S. net sales from 13.5% and increasing up to 24.0% if annual net sales exceed $900.0 million. There will be a 50.0% reduction to these royalties if a biosimilar to OCREVUS is approved in the U.S.

In addition, we receive a gross 3.0% royalty on net sales of OCREVUS outside the U.S., with the royalty period lasting 11 years from the first commercial sale of OCREVUS on a country-by-country basis.

The commercialization of OCREVUS does not impact the percentage of the co-promotion profits we receive for RITUXAN, LUNSUMIO or GAZYVA. Genentech is solely responsible for development and commercialization of OCREVUS and funding future costs. Genentech cannot develop OCREVUS in CLL, non-Hodgkin's lymphoma or rheumatoid arthritis.

OCREVUS royalty revenue is based on our estimates from third party and market research data of OCREVUS sales occurring during the corresponding period. Differences between actual and estimated royalty revenue will be adjusted for in the period in which they become known, which is generally expected to be the following quarter.

If we undergo a change in control, as defined in our collaboration agreement, Genentech will be deemed to have purchased our rights to OCREVUS in exchange for the continued payment of the current royalties on net sales (as defined in our collaboration agreement and summarized above) in the U.S. only, until the 11 year anniversary of the first commercial sale of OCREVUS in the U.S.

LUNSUMIO (mosunetuzumab)

In January 2022 we exercised our option with Genentech to participate in the joint development and commercialization of LUNSUMIO. In connection with this exercise, we recorded a $30.0 million option exercise fee payable to Genentech in December 2021, which was recognized in research and development expense in our consolidated statements of income for the year ended December 31, 2021. We also recorded a charge of approximately $20.0 million to reimburse Genentech for our 30.0% share of the costs incurred in developing this product candidate during 2021, which was recognized in research and development expense in our consolidated statements of income for the year ended December 31, 2021. For the year ended December 31, 2022, we recorded approximately $28.4 million in research and development expense and approximately $13.0 million in sales and marketing expense in our consolidated statements of income related to this collaboration. For the year ended December 31, 2023, we began to record our share of LUNSUMIO development and sales and marketing expense as a reduction of our share of pre-tax profits in revenue from anti-CD20 therapeutic programs within our consolidated statements of income.

Under our collaboration with Genentech, we were responsible for 30.0% of development costs for LUNSUMIO prior to FDA approval and will be entitled to a tiered share of co-promotion operating profits and losses in the U.S., as summarized in the table below. In addition, we receive low single-digit royalties on sales of LUNSUMIO outside the U.S. In December 2022 LUNSUMIO was granted accelerated approval by the FDA for the treatment of relapsed or refractory follicular lymphoma.

If we undergo a change in control, as defined in our collaboration agreement, Genentech will be deemed to have purchased our rights to LUNSUMIO in exchange for 30.0% of the U.S. co-promotion operating profits or losses until the 11 year anniversary of the first commercial sale of LUNSUMIO in the U.S.

COLUMVI (glofitamab)

In December 2022 we entered into an agreement with Genentech related to the commercialization and sharing of economics for COLUMVI, a bispecific antibody for the treatment of B-cell non-Hodgkin's lymphoma, which was subsequently granted accelerated approval by the FDA in June 2023. Under the terms of this agreement, we will have no payment obligations. Genentech will have sole decision-making rights on the commercialization of COLUMVI within the U.S. and we will receive tiered royalties in the mid-single digit range on net sales of COLUMVI in the U.S. The commercialization of COLUMVI does not impact the percentage of the co-promotion profits we receive for RITUXAN, LUNSUMIO or GAZYVA.

If we undergo a change in control, as defined in our collaboration agreement, Genentech will be deemed to have purchased our rights to COLUMVI in exchange for a mid-single digit royalty on net sales (as defined in our collaboration agreement) in the U.S. only, until the 11 year anniversary of the first commercial sale of the product in the U.S.

Profit-sharing Formulas

RITUXAN and LUNSUMIO Profit Share

Our current pretax co-promotion profit-sharing formula for RITUXAN and LUNSUMIO in the U.S. provides for a 30.0% share on the first $50.0 million of combined co-promotion operating profits earned each calendar year. As a result of the FDA approval of LUNSUMIO our share of the combined annual co-promotion profits for RITUXAN and LUNSUMIO in excess of $50.0 million varies upon the following events, as summarized in the table below:




After LUNSUMIO Approval until the First Threshold Date	37.5	%
After First Threshold Date until the Second Threshold Date	35.0	%
After Second Threshold Date	30.0	%

First Threshold Date means the earlier of (i) the first day of the calendar quarter following the date U.S. gross sales of GAZYVA within any consecutive 12-month period have reached $500.0 million or (ii) the first date in any calendar year in which U.S. gross sales of LUNSUMIO have reached $150.0 million.

Second Threshold Date means the later of (i) the first date the gross sales in any calendar year in which U.S. gross sales of LUNSUMIO reach $350.0 million or (ii) January 1 of the calendar year following the calendar year in which the First Threshold Date occurs.

In March 2023 the First Threshold Date was achieved. As a result, beginning in April 2023 the pre-tax profit share for RITUXAN and LUNSUMIO was 35.0%. Our share of RITUXAN pre-tax profits in the U.S. in excess of $50.0 million for the years ended December 31, 2022 and 2021, was 37.5%.

GAZYVA Profit Share

Our current pretax profit-sharing formula for GAZYVA provides for a 35.0% share on the first $50.0 million of operating profits earned each calendar year. Our share of annual co-promotion profits in excess of $50.0 million varies upon the following events, as summarized in the table below:



Until Second GAZYVA Threshold Date	37.5	%
After Second GAZYVA Threshold Date	35.0	%

Second GAZYVA Threshold Date means the first day of the calendar quarter following the date U.S. gross sales of GAZYVA within any consecutive 12-month period have reached $500.0 million. The Second GAZYVA Threshold Date can be achieved regardless of whether GAZYVA has been approved in a non-CLL indication.

In March 2023 the Second GAZYVA Threshold Date was achieved. As a result, beginning in April 2023 the pre-tax profit share for GAZYVA was 35.0%. Our share of GAZYVA pre-tax profits in excess of $50.0 million for the years ended December 31, 2022 and 2021, was 37.5%.

Revenue from Anti-CD20 Therapeutic Programs

Revenue from anti-CD20 therapeutic programs is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Royalty revenue on sales of OCREVUS	$	1,266.2	$	1,136.3	$	991.7
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4		547.0		647.7
Other revenue from anti-CD20 therapeutic programs	14.0		17.2		19.1
Total revenue from anti-CD20 therapeutic programs	$	1,689.6	$	1,700.5	$	1,658.5

(1) LUNSUMIO became commercially available in the U.S. during the first quarter of 2023.

Prior to regulatory approval, we record our share of the expense incurred by the collaboration for the development of anti-CD20 products in research and development expense and pre-commercialization costs within selling, general and administrative expense in our consolidated statements of income. After an anti-CD20 product is approved, we record our share of the development and sales and marketing expense related to that product as a reduction of our share of pre-tax profits in revenue from anti-CD20 therapeutic programs.

Ionis Pharmaceuticals, Inc.

SPINRAZA

In January 2012 we entered into a collaboration and license agreement with Ionis pursuant to which we have an exclusive, worldwide license to develop and commercialize SPINRAZA for the treatment of SMA.

Under our agreement with Ionis, we make royalty payments to Ionis on annual worldwide net sales of SPINRAZA using a tiered royalty rate between 11.0% and 15.0%, which are recognized in cost of sales within our consolidated statements of income. Royalty cost of sales related to sales of SPINRAZA for the years ended December 31, 2023, 2022 and 2021, totaled approximately $240.2 million, $243.1 million and $267.1 million, respectively.

2018 Ionis Agreement

In June 2018 we entered into a 10-year exclusive collaboration agreement with Ionis to develop novel ASO drug candidates for a broad range of neurological diseases for a total payment of $1.0 billion, consisting of an upfront payment of $375.0 million and the purchase of approximately 11.5 million shares of Ionis common stock at a cost of $625.0 million.

Upon closing, we recorded $50.9 million of the $375.0 million upfront payment as prepaid services in our consolidated balance sheets and recognized the remaining $324.1 million as research and development expense in

our consolidated statements of income. The amount recorded as prepaid services represented the value of the employee resources committed to the arrangement to provide research and discovery services over the term of the agreement.

We have the option to license therapies arising out of this agreement and will be responsible for the development and commercialization of such therapies. We may pay development milestones to Ionis of up to $125.0 million or $270.0 million for each program, depending on the indication plus an annual license fee, as well as royalties on potential net commercial sales.

During the years ended December 31, 2023, 2022 and 2021, we incurred milestones of $7.5 million, $10.0 million and $22.5 million, respectively, related to the advancement of neurological targets identified under this agreement, which were recorded as research and development expense in our consolidated statements of income.

2017 SMA Collaboration Agreement

In December 2017 we entered into a collaboration agreement with Ionis to identify new ASO drug candidates for the potential treatment of SMA. Under this agreement, we have the option to license therapies arising out of this collaboration and will be responsible for their development and commercialization of such therapies.

Upon entering into this agreement, we made a $25.0 million upfront payment to Ionis and we may pay Ionis up to $260.0 million in additional development and regulatory milestone payments if new drug candidates advance to marketing approval. Upon commercialization, we may also pay Ionis up to $800.0 million in additional performance-based milestone payments and tiered royalties on potential net sales of such therapies.

In December 2021 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize BIIB115, an investigational ASO in development for SMA. In connection with this option exercise, we made an opt-in payment of $60.0 million to Ionis, which was recorded as research and development expense in our consolidated statements of income for the year ended December 31, 2021.

2013 Long-term Strategic Research Agreement

In September 2013 we entered into a six-year research collaboration agreement with Ionis under which both companies collaborate to perform discovery level research and subsequent development and commercialization activities of antisense or other therapeutics for the potential treatment of neurological diseases. Under this agreement, Ionis performs research on a set of neurological targets identified within the agreement.

Ionis is eligible to receive milestone payments, license fees and royalty payments for all product candidates developed through this collaboration, with the specific amount dependent upon the modality of the product candidate advanced by us under the terms of the agreement.

For non-ALS antisense product candidates, Ionis is responsible for global development through the completion of a Phase 2 trial and we provide advice on the clinical trial design and regulatory strategy. For ALS antisense product candidates, we are responsible for global development, clinical trial design and regulatory strategy. We have an option to license a product candidate until completion of the Phase 2 trial. If we exercise our option, we will pay Ionis up to a $70.0 million license fee and assume global development, regulatory and commercialization responsibilities. Ionis could receive additional milestone payments upon the achievement of certain regulatory milestones of up to $130.0 million, plus additional amounts related to the cost of clinical trials conducted by Ionis under the collaboration, and royalties on future sales if we successfully develop the product candidate after option exercise.

In December 2018 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize QALSODY (tofersen), for the treatment of ALS with SOD1 mutations. Following the option exercise, we are solely responsible for the costs and expense related to the development, manufacturing and commercialization of QALSODY. We may pay post-licensing milestone payments to Ionis of up to $55.0 million based on the successful achievement of certain regulatory and commercial milestones.

In April 2023 the FDA approved QALSODY for the treatment of ALS in adults who have a mutation in the SOD1 gene. This indication is approved under accelerated approval based on reduction in plasma neurofilament light chain observed in patients treated with QALSODY. Continued approval for this indication may be contingent upon verification of clinical benefit in confirmatory trial(s). Under this agreement, we make royalty payments to Ionis on annual worldwide net sales of QALSODY using a tiered royalty rate between 11.0% and 15.0%, which are recognized in cost of sales within our consolidated statements of income.

During the year ended December 31, 2023, we incurred a milestone payment of $16.0 million to Ionis following the FDA's approval of QALSODY, which was recorded within intangible assets, net in our consolidated balance sheets. We may pay Ionis an additional milestone of $20.0 million if QALSODY receives regulatory approval in the E.U.

During the years ending December 31, 2022 and 2021, we incurred milestones of $17.0 million and $10.0 million, respectively, related to the advancement of programs under this agreement, which were recorded as research and development expense in our consolidated statements of income.

2012 Ionis Agreement

In December 2012 we entered into an agreement with Ionis for the development and commercialization of up to three gene targets.

Under this agreement, Ionis is responsible for global development of any product candidate through the completion of a Phase 2 trial and we will provide advice on the clinical trial design and regulatory strategy. We have an option to license the product candidate until completion of the Phase 2 trial. If we exercise our option, we will pay a license fee of up to $70.0 million to Ionis and assume global development, regulatory and commercialization responsibilities. Ionis is eligible to receive up to $130.0 million in additional milestone payments upon the achievement of certain regulatory milestones as well as royalties on future sales if we successfully develop the product candidate after option exercise.

In December 2019 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize BIIB080 (tau ASO), which is currently in Phase 2 development for the potential treatment of Alzheimer's disease. In connection with the option exercise, we made a payment of $45.0 million to Ionis, which was recorded as research and development expense in our consolidated statements of income. Future payments may include additional milestone payments of up to $155.0 million and royalties on future sales in the low- to mid-teens if we successfully develop the product candidate after option exercise.

During the year ended December 31, 2022, we incurred a milestone payment of $10.0 million, related to the advancement of BIIB080 under this agreement, which was recorded within research and development expense in our consolidated statements of income.

Eisai Co., Ltd.

During the first quarter of 2023 we accrued a $31.0 million payable to Eisai related to the termination of an agreement whereby Eisai co-promoted or distributed our MS products in certain Asia-Pacific markets and settings. As of December 31, 2023, we paid approximately $16.0 million of the $31.0 million payable. The remaining portion was subsequently paid in January 2024. This termination fee is included in selling, general and administrative expense in our consolidated statements of income for the year ended December 31, 2023.

LEQEMBI (lecanemab) Collaboration

We have a collaboration agreement with Eisai to jointly develop and commercialize LEQEMBI (lecanemab), an anti-amyloid antibody for the treatment of Alzheimer's disease (the LEQEMBI Collaboration).

Eisai serves as the lead of LEQEMBI development and regulatory submissions globally with both companies co-commercializing and co-promoting the product, and Eisai having final decision-making authority. All costs, including research, development, sales and marketing expense, are shared equally between us and Eisai. We and Eisai co-promote LEQEMBI and share profits and losses equally. We currently manufacture LEQEMBI drug substance and drug product and in March 2022 we extended our supply agreement with Eisai related to LEQEMBI from five years to ten years for the manufacture of LEQEMBI drug substance.

The LEQEMBI Collaboration also provided Eisai with an option to jointly develop and commercialize ADUHELM (aducanumab) (ADUHELM Option), and an option to jointly develop and commercialize one of our anti-tau monoclonal antibodies (Anti-Tau Option). In October 2017 Eisai exercised its ADUHELM Option and we entered into a new collaboration agreement for the joint development and commercialization of ADUHELM (aducanumab) (the ADUHELM Collaboration Agreement).

On March 14, 2022, we amended our ADUHELM Collaboration Agreement with Eisai. As of the amendment date, we have sole decision making and commercialization rights worldwide on ADUHELM, and beginning January 1, 2023, Eisai receives only a tiered royalty based on net sales of ADUHELM, and no longer participates in sharing ADUHELM's global profits and losses. In March 2022 we also amended the LEQEMBI Collaboration Agreement with Eisai to eliminate the Anti-Tau Option.

If either company undergoes a change of control, as defined in our LEQEMBI Collaboration Agreement, the non-acquired party may elect to initiate an operational separation, as defined in the LEQEMBI Collaboration Agreement. In the event of an operational separation, we would work with Eisai to effect a timely transition of any development, manufacturing or commercial responsibilities regarding LEQEMBI from us to Eisai. In this scenario, as of six months following the change of control, our ongoing responsibility for LEQEMBI related cost-sharing would be reduced to an amount equal to 80.0% of what we would have owed prior to the operational separation, and all other economic rights would remain unchanged.

In addition, in the event either company undergoes a change of control in which the acquirer is engaged in commercialization of a competing product, as defined in the LEQEMBI Collaboration Agreement, the non-acquired party may also request that the acquired party cease commercializing the competing product. Should the acquired party elect to continue commercializing the competing product, the non-acquired party may terminate the LEQEMBI Collaboration Agreement. Furthermore, in the event we are the non-acquired party, we may choose either to sell our interest in LEQEMBI to Eisai or purchase Eisai's interest in LEQEMBI, subject to the parameters set forth in the LEQEMBI Collaboration Agreement.

In July 2023 the FDA granted traditional approval of LEQEMBI. Prior to receiving traditional approval, LEQEMBI had been granted accelerated approval by the FDA in January 2023, at which time it became commercially available in the U.S. Additionally, in September 2023 the Japanese Ministry of Health, Labor and Welfare approved LEQEMBI in Japan, which was subsequently launched in Japan in December 2023.

Upon commercialization of LEQEMBI, we began recognizing our 50.0% share of LEQEMBI product revenue, net and cost of sales, including royalties, within other revenue in our consolidated statements of income, as we are not the principal.

Our share of LEQEMBI sales and marketing expense and development expense are recorded within selling, general and administrative expense and research and development expense, respectively, within our consolidated statements of income.

A summary of development and sales and marketing expense related to the LEQEMBI Collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	371.9	$	347.2	$	323.0
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our consolidated statements of income	186.0		173.6		161.5
Total sales and marketing expense incurred by the LEQEMBI Collaboration	304.4		104.6		27.2
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	152.2		52.3		13.6

ADUHELM Collaboration Agreement

The LEQEMBI Collaboration also provided Eisai with an option to jointly develop and commercialize ADUHELM (aducanumab) (ADUHELM Option). In October 2017 Eisai exercised its ADUHELM Option and we entered into a new collaboration agreement for the joint development and commercialization of ADUHELM (the ADUHELM Collaboration Agreement).

Under our initial ADUHELM Collaboration Agreement, we would lead the ongoing development of ADUHELM, and we and Eisai would co-promote ADUHELM with a region-based profit split. Beginning in 2019, Eisai was reimbursing us for 45.0% of development and sales and marketing expense incurred by the collaboration for the advancement of ADUHELM.

In March 2022 we amended our ADUHELM Collaboration Agreement with Eisai. As of the amendment date, we have sole decision making and commercialization rights worldwide on ADUHELM, and beginning January 1, 2023, Eisai receives only a tiered royalty based on net sales of ADUHELM, and no longer participates in sharing ADUHELM's global profits and losses. Eisai's share of development, commercialization and manufacturing expense was limited to $335.0 million for the period from January 1, 2022 to December 31, 2022, which was achieved as of December 31, 2022. Once this limit was achieved, we became responsible for all ADUHELM related costs.

A summary of development expense, sales and marketing expense and milestone payments related to our initial ADUHELM Collaboration Agreement is as follows:


	For the Year Ended December 31,
(In millions)	2022		2021
Total ADUHELM Collaboration development expense	$	149.4	$	183.7
Biogen's share of the ADUHELM Collaboration development expense reflected in research and development expense in our consolidated statements of income	82.2		101.1
Total sales and marketing expense incurred by the ADUHELM Collaboration	134.2		562.3
Biogen's share of the ADUHELM Collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	71.5		301.4
Total ADUHELM Collaboration third party milestones	—		100.0
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	—		45

ADUHELM Co-promotion Profits and Losses

Under our initial ADUHELM Collaboration Agreement, we recognized revenue on sales of ADUHELM in the U.S. to third parties as a component of product revenue, net in our consolidated statements of income. We also recorded the related cost of revenue and sales and marketing expense in our consolidated statements of income as these costs were incurred. Payments made to and received from Eisai for its 45.0% share of the co-promotion profits or losses in the U.S. were recognized in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income. For the years ended December 31, 2022 and 2021, we recognized net reductions to our operating expense of approximately $224.7 million and $233.2 million, respectively, to reflect Eisai's 45.0% share of net collaboration losses in the U.S. for ADUHELM.

For the year ended December 31, 2021, we recognized a net reduction to our operating expense of $45.0 million to reflect Eisai's 45.0% share of the $100.0 million milestone payment made to Neurimmune related to the launch of ADUHELM in the U.S., which was recorded in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income.

During the fourth quarter of 2021 we recorded approximately $164.0 million of charges associated with the write-off of inventory and purchase commitments in excess of forecasted demand related to ADUHELM. During the first quarter of 2022, as a result of the final NCD, we recorded approximately $275.0 million of charges associated with the write-off of inventory and purchase commitments in excess of forecasted demand related to ADUHELM. Additionally, for the years ended December 31, 2022 and 2021, we recorded approximately $111.0 million and $30.0 million, respectively, of aggregate gross idle capacity charges related to ADUHELM. These charges were recorded in cost of sales within our consolidated statements of income for the years ended December 31, 2022 and 2021.

We recognized approximately $197.0 million and $99.0 million related to Eisai's 45.0% share of inventory, idle capacity charges and contractual commitments in collaboration profit sharing/(loss reimbursement) within our consolidated statements of income for the years ended December 31, 2022 and 2021, respectively.

Amounts receivable from Eisai related to the agreements discussed above were approximately $1.4 million and $88.0 million as of December 31, 2023 and 2022, respectively. Amounts payable to Eisai related to the agreements discussed above were approximately $118.4 million and $81.2 million as of December 31, 2023 and 2022, respectively.

UCB

We have a collaboration agreement with UCB, effective November 2003, to jointly develop and commercialize dapirolizumab pegol, an anti-CD40L pegylated Fab, for the potential treatment of SLE and other future agreed

indications. Either we or UCB may propose development of dapirolizumab pegol in additional indications. If the parties do not agree to add an indication as an agreed indication to the collaboration, we or UCB may, at the sole expense of the applicable party, pursue development in such excluded indication(s), subject to an opt-in right of the non-pursuing party after proof of clinical activity.

All costs incurred for agreed indications, including research, development, sales and marketing expense, are shared equally between us and UCB. If marketing approval is obtained, both companies will co-promote dapirolizumab pegol and share profits and losses equally.

A summary of development expense related to the UCB collaboration agreement is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total UCB collaboration development expense	$	60.7	$	68.0	$	84.2
Biogen's share of the UCB collaboration development expense reflected in research and development expense in our consolidated statements of income	30.3		34.0		42.1

Alkermes

In November 2017 we entered into an exclusive license and collaboration agreement with Alkermes Pharma Ireland Limited, a subsidiary of Alkermes, for VUMERITY, a novel fumarate for the treatment of RMS. In October 2019 the FDA approved VUMERITY in the U.S. for the treatment of RMS. During the fourth quarter of 2021 VUMERITY was approved for the treatment of RRMS in certain international markets.

Under this agreement, we received an exclusive, worldwide license to develop and commercialize VUMERITY and we pay Alkermes royalties of 15.0% on worldwide net commercial sales of VUMERITY, which are recognized in cost of sales within our consolidated statements of income. Royalties payable on net commercial sales of VUMERITY are subject, under certain circumstances, to tiered minimum annual payment requirements for a period of five years following FDA approval. Royalty cost of sales related to sales of VUMERITY for the years ended December 31, 2023, 2022 and 2021, totaled approximately $87.4 million, $83.0 million and $61.6 million, respectively.

Alkermes is eligible to receive royalties in the high-single digits to sub-teen double digits of annual net commercial sales upon successful development and commercialization of new product candidates, other than VUMERITY, developed under the exclusive license from Alkermes.

Alkermes currently supplies both VUMERITY and FAMPYRA to us pursuant to separate supply agreements. In October 2019 we entered into a new supply agreement and amended our license and collaboration agreement with Alkermes for VUMERITY. We have elected to initiate a technology transfer and, following a transition period, to manufacture VUMERITY or have VUMERITY manufactured by a third party we have engaged in exchange for paying an increased royalty rate to Alkermes on any portion of future worldwide net commercial sales of VUMERITY that is manufactured by us or our designee. In January 2023 we entered into a new supply agreement with Alkermes for FAMPYRA through January 2025. In December 2023 Alkermes entered into a definitive agreement to sell its development and manufacturing facility to Novo Nordisk, which is expected to close in mid-2024. Alkermes and Novo Nordisk plan to enter into subcontracting arrangements to continue work currently performed at the facility for a period of time after closing the transaction, which may continue through the end of 2025.

Acorda Therapeutics, Inc.

In June 2009 we entered into a collaboration and license agreement with Acorda to develop and commercialize products containing fampridine, such as FAMPYRA, in markets outside the U.S.

Under this agreement, we pay tiered royalties based on the level of ex-U.S. net sales and we may pay potential milestone payments based on the successful achievement of certain regulatory and commercial milestones.

In January 2024 we notified Acorda of our decision to terminate our collaboration and license agreement, effective January 1, 2025. As a result of this termination, Acorda will regain global commercialization rights to FAMPYRA.

For the years ended December 31, 2023, 2022 and 2021, total cost of sales related to royalties and commercial supply of FAMPYRA reflected in our consolidated statements of income were approximately $55.2 million, $46.1 million and $46.6 million, respectively.

Sage Therapeutics, Inc.

In November 2020 we entered into a global collaboration and license agreement with Sage to jointly develop and commercialize ZURZUVAE (zuranolone) for the treatment of PPD and potential treatment of MDD and BIIB124 (SAGE-324) for the potential treatment of essential tremor with potential in other neurological conditions such as epilepsy.

In connection with the closing of this transaction in December 2020 we purchased $650.0 million of Sage common stock, or approximately 6.2 million shares at approximately $104.14 per share, which were initially subject to transfer restrictions. We may pay Sage development and commercial milestone payments that could total up to approximately $1.6 billion if all the specified milestones set forth in this collaboration are achieved.

In August 2023 the FDA approved ZURZUVAE for adults with PPD, pending DEA scheduling, which was completed in October 2023. Upon approval, ZURZUVAE became the first and only oral, once-daily, 14-day treatment that can provide rapid improvements in depressive symptoms by day 15 for women with PPD. ZURZUVAE for PPD became commercially available in the U.S. during the fourth quarter of 2023. Additionally, the FDA issued a CRL for the NDA for zuranolone in the treatment of adults with MDD. The CRL stated that the application did not provide substantial evidence of effectiveness to support the approval of zuranolone for the treatment of MDD and that an additional study or studies would be needed. We and Sage are continuing to seek feedback from the FDA and evaluating next steps.

Under this collaboration, both companies will share equal responsibility and costs for development as well as profits and losses for commercialization in the U.S. Outside of the U.S., we are responsible for development and commercialization, excluding Japan, Taiwan and South Korea, with respect to zuranolone and may pay Sage potential tiered royalties in the high teens to low twenties. During the fourth quarter of 2023 we accrued a milestone payment due to Sage of $75.0 million upon the first commercial sale of ZURZUVAE for PPD in the U.S., which was recorded within intangible assets, net in our consolidated balance sheets, and subsequently paid in January 2024.

For the year ended December 31, 2023, we recognized net reductions to our operating expense of approximately $4.7 million to reflect Sage's 50.0% share of net collaboration losses in the U.S., which is recognized in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income.

A summary of development and sales and marketing expense related to the Sage collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total Sage collaboration development expense	$	176.7	$	173.3	$	167.7
Biogen's share of the Sage collaboration development expense reflected in research and development expense in our consolidated statements of income	88.3		86.7		83.8
Total sales and marketing expense incurred by the Sage collaboration	187.0		109.9		36.4
Biogen's share of the Sage collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our consolidated statements of income	93.5		55.0		18.2

Denali Therapeutics Inc.

In August 2020 we entered into a collaboration and license agreement with Denali to co-develop and co-commercialize Denali's small molecule inhibitors of LRRK2 for Parkinson's disease (LRRK2 Collaboration) and also entered into a separate agreement to obtain an exclusive option to license two preclinical programs from Denali's Transport Vehicle platform, including its ATV-enabled anti-amyloid beta program and a second program utilizing its Transport Vehicle technology.

As part of this collaboration we purchased $465.0 million of Denali common stock in September 2020, or approximately 13 million shares at approximately $34.94 per share, which were initially subject to transfer restrictions. We may pay Denali development and commercial milestone payments that could total up to approximately $1.1 billion if the milestones related to the LRRK2 Collaboration are achieved.

In April 2023 we exercised our option with Denali to license the ATV-enabled anti-amyloid beta program. In connection with this exercise, we assumed responsibility for all development and commercial activities and associated expenses related to this program. In addition, we made a one-time option exercise payment to Denali and, should certain milestones be achieved, may pay Denali additional development and commercial milestone payments and royalties based on future net sales. Our agreement with Denali was amended in August 2023, whereby certain milestone criteria were changed, while the total amount of development, regulatory and commercial milestones remains the same. In addition, we agreed to waive our option right to the second option program.

Under the LRRK2 Collaboration, both companies share responsibility and costs for global development based on specified percentages as well as profits and losses for commercialization in the U.S. and China. Outside the U.S. and China we are responsible for commercialization and may pay Denali potential tiered royalties.

A summary of development expense related to the Denali collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total Denali collaboration development expense	$	65.0	$	75.1	$	42.5
Biogen's share of the Denali collaboration development expense reflected in research and development expense in our consolidated statements of income	39.0		43.8		25.5

Sangamo Therapeutics, Inc.

In February 2020 we entered into a collaboration and license agreement with Sangamo to pursue certain neurological targets leveraging Sangamo’s proprietary zinc finger protein technology delivered via adeno-associated virus to modulate the expression of key genes involved in neurological diseases.

In connection with the closing of this transaction in April 2020 we purchased $225.0 million of Sangamo common stock, or approximately 24 million shares at approximately $9.21 per share, which were initially subject to transfer restrictions. These restrictions have now lapsed.

In March 2023 we terminated our collaboration and license agreement with Sangamo.

A summary of development expense related to the Sangamo collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Total Sangamo collaboration development expense	$	4.1	$	19.1	$	22.7
Biogen's share of the Sangamo collaboration development expense reflected in research and development expense in our consolidated statements of income	2.4		12.1		14.6

InnoCare Pharma Limited

In July 2021 we entered into a collaboration and license agreement with InnoCare Pharma Limited (InnoCare) for orelabrutinib, an oral small molecule Bruton's tyrosine kinase inhibitor for the potential treatment of MS. In connection with the closing of this transaction in August 2021 we made an upfront payment of $125.0 million that was recorded as research and development expense within our consolidated statements of income for the year ended December 31, 2021.

In February 2023 we terminated our collaboration and license agreement with InnoCare for orelabrutinib, for the potential treatment of MS.

Other Research and Discovery Arrangements

These arrangements may include the potential for future milestone payments based on the achievement of certain clinical and commercial development payable over a period of several years.

Other

For the years ended December 31, 2023, 2022 and 2021, we recorded approximately $4.1 million, $39.2 million and $89.1 million, respectively, as research and development expense in our consolidated statements of income related to other research and discovery related arrangements.

Samsung Bioepis Co., Ltd.

Joint Venture Agreement

In February 2012 we entered into a joint venture agreement with Samsung BioLogics establishing an entity, Samsung Bioepis, to develop, manufacture and market biosimilar products. Samsung BioLogics contributed 280.5 billion South Korean won (approximately $250.0 million) for an 85.0% ownership interest in Samsung Bioepis and we contributed 49.5 billion South Korean won (approximately $45.0 million) for the remaining 15.0% ownership interest. In June 2018 we exercised our option under our joint venture agreement to increase our ownership percentage in Samsung Bioepis from approximately 5.0%, which reflected the effect of previous equity financings in which we did not participate, to approximately 49.9%. The share purchase transaction was completed in November 2018 and, upon closing, we paid 759.5 billion South Korean won ($676.6 million) to Samsung BioLogics.

As part of this transaction, we are also eligible to receive up to an additional $50.0 million upon the achievement of certain commercial milestones. Our policy for contingent payments of this nature is to recognize the payments in the period that they become realizable, which is generally the same period in which the payments are earned.

Prior to this sale, we recognized our share of the results of operations related to our investment in Samsung Bioepis under the equity method of accounting one quarter in arrears when the results of the entity became available, which was reflected as equity in (income) loss of investee, net of tax in our consolidated statements of income.

Upon our November 2018 investment, the equity method of accounting required us to identify and allocate differences between the fair value of our investment and the carrying value of our interest in the underlying net assets of the investee. These basis differences were being amortized over their economic life, until the completion of the sale in April 2022, as discussed above. The total basis difference was approximately $675.0 million and related to inventory, developed technology, IPR&D and deferred tax balances. The basis differences related to inventory were amortized, net of tax, over their estimated useful lives of 1.5 years, and the basis differences related to developed technology and IPR&D for marketed products were being amortized, net of tax, over their estimated useful lives of 15 years.

For the year ended December 31, 2022, we recognized net income on our investment of $2.6 million, reflecting our share of Samsung Bioepis' operating profits, net of tax, totaling $17.0 million offset by amortization of basis differences totaling $14.4 million. Following the sale of Samsung Bioepis we no longer recognize gains or losses associated with Samsung Bioepis' results of operations and amortization related to basis differences.

For the year ended December 31, 2021, we recognized net income on our investment of $34.9 million, reflecting our share of Samsung Bioepis' operating profits, net of tax, totaling $64.6 million offset by amortization of basis differences totaling $29.7 million.

Net income on our investment for the year ended December 31, 2021, reflects a $31.2 million benefit related to the release of a valuation allowance on deferred tax assets associated with Samsung Bioepis. The valuation allowance was released in the second quarter of 2021 based on a consideration of the positive and negative evidence, including the historic earnings of Samsung Bioepis.

For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

2019 Development and Commercialization Agreement

In December 2019 we completed a transaction with Samsung Bioepis and secured the exclusive rights to commercialize two potential ophthalmology biosimilar products, BYOOVIZ (ranibizumab-nuna), a ranibizumab biosimilar referencing LUCENTIS, and SB15, a proposed aflibercept biosimilar referencing EYLEA, in major markets worldwide, including the U.S., Canada, Europe, Japan and Australia. Samsung Bioepis will be responsible for development and will supply both products to us at a pre-specified gross margin of approximately 45.0%.

During the third quarter of 2021 we accrued $15.0 million in milestone payments related to the approval of BYOOVIZ in the U.S., the E.U. and the U.K., that were capitalized within intangible assets, net in our consolidated balance sheets. We may also pay Samsung Bioepis up to approximately $180.0 million in additional development, regulatory and sales-based milestones.

2013 Commercial Agreement

In December 2013 we entered into an agreement with Samsung Bioepis to commercialize, over a 10-year term, 3 anti-TNF biosimilar product candidates which includes IMRALDI, an adalimumab biosimilar referencing HUMIRA, FLIXABI, an infliximab biosimilar referencing REMICADE, and BENEPALI, an etanercept biosimilar referencing ENBREL, in Europe, and in the case of BENEPALI, Japan. We have an option to extend this agreement by an additional five years, subject to payment of an option exercise fee of $60.0 million by August 2024. We also have an option to acquire exclusive rights to commercialize these products in China.

We reflect revenue on sales of BENEPALI, IMRALDI and FLIXABI to third parties in product revenue, net in our consolidated statements of income and record the related cost of revenue and sales and marketing expense in our consolidated statements of income to their respective line items when these costs are incurred. Royalty payments to AbbVie on sales of IMRALDI are recognized in cost of sales within our consolidated statements of income.

We share 50.0% of the profit or loss related to our commercial agreement with Samsung Bioepis, which is recognized in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income. For the years ended December 31, 2023, 2022 and 2021, we recognized net profit-sharing expense of $223.5 million, $217.4 million and $285.4 million, respectively, to reflect Samsung Bioepis' 50.0% sharing of the net collaboration profits.

Other Services

Simultaneous with the formation of Samsung Bioepis, we also entered into a license agreement with Samsung Bioepis.

Under this license agreement, we granted Samsung Bioepis an exclusive license to use, develop, manufacture and commercialize biosimilar products created by Samsung Bioepis using Biogen product-specific technology. In exchange, we receive single digit royalties on biosimilar products developed and commercialized by Samsung Bioepis. Royalty revenue under the license agreement is recognized as a component of contract manufacturing, royalty and other revenue in our consolidated statements of income.

For the years ended December 31, 2023, 2022 and 2021, we recognized $13.6 million, $20.6 million and $20.7 million, respectively, as a component of contract manufacturing, royalty and other revenue in our consolidated statements of income related to the license agreement and other services performed under our collaboration with Samsung Bioepis.

Amounts receivable from Samsung Bioepis related to the agreements discussed above were $9.9 million and $2.0 million as of December 31, 2023 and 2022, respectively. Amounts payable to Samsung Bioepis related to the agreements discussed above were $73.7 million and $40.5 million as of December 31, 2023 and 2022, respectively.

Equity

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Equity


Note 14:			Equity

Preferred Stock

We have 8.0 million shares of Preferred Stock authorized, of which 1.75 million shares are authorized as Series A, 1.0 million shares are authorized as Series X junior participating and 5.25 million shares are undesignated. Shares may be issued without a vote or action of shareholders from time to time in classes or series with the designations, powers, preferences and the relative, participating, optional or other special rights of the shares of each such class or series and any qualifications, limitations or restrictions thereon as set forth in the instruments governing such shares. Any such Preferred Stock may rank prior to common stock as to dividend rights, liquidation preference or both, and may have full or limited voting rights and may be convertible into shares of common stock. No shares of Preferred Stock were issued and outstanding during 2023, 2022 and 2021.

Common Stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2023, 2022 and 2021:

As of December 31, 2023

As of December 31, 2022

As of December 31, 2021

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

168.7

144.9

1,000.0

167.9

144.0

1,000.0

170.8

147.0

Share Repurchases

In October 2020 our Board of Directors authorized our 2020 Share Repurchase Program, which is a program to repurchase up to $5.0 billion of our common stock. Our 2020 Share Repurchase Program does not have an expiration date. All share repurchases under our 2020 Share Repurchase Program will be retired. Under our 2020 Share Repurchase Program, we repurchased and retired approximately 3.6 million and 6.0 million shares of our common stock at a cost of approximately $750.0 million and $1.8 billion during the years ended December 31, 2022 and 2021, respectively. There were no share repurchases of our common stock during the year ended December 31, 2023. Approximately $2.1 billion remained available under our 2020 Share Repurchase Program as of December 31, 2023.

Amounts paid to repurchase shares in excess of their par value are allocated between additional paid-in capital and retained earnings, with payments in excess of our additional paid-in-capital balance recorded as a reduction to retained earnings.

In August 2022 the IRA was signed into law. Among other things, the IRA levies a 1.0% excise tax on net stock repurchases after December 31, 2022. While we have historically made discretionary share repurchases, we had no share repurchases of our common stock during the year ended December 31, 2023.

Accumulated Other Comprehensive Income (Loss)

The following tables summarize the changes in AOCI, net of tax by component:


	December 31, 2023
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2022	$	(15.7)	$	15.1	$	(1.1)	$	(163.2)	$	(164.9)
Other comprehensive income (loss) before reclassifications	2.3		(26.8)		(1.5)		37.1		11.1
Amounts reclassified from AOCI	13.4		(13.3)		—		—		0.1
Net current period other comprehensive income (loss)	15.7		(40.1)		(1.5)		37.1		11.2
Balance, December 31, 2023	$	—	$	(25.0)	$	(2.6)	$	(126.1)	$	(153.7)


	December 31, 2022
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Gains (Losses) on Net Investment Hedges, Net of Tax(1)		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2021	$	(2.2)	$	53.8	$	25.5	$	(44.8)	$	(139.0)	$	(106.7)
Other comprehensive income (loss) before reclassifications	(23.5)		137.3		12.6		43.7		(83.1)		87.0
Amounts reclassified from AOCI	10.0		(176.0)		(38.1)		—		58.9		(145.2)
Net current period other comprehensive income (loss)	(13.5)		(38.7)		(25.5)		43.7		(24.2)		(58.2)
Balance, December 31, 2022	$	(15.7)	$	15.1	$	—	$	(1.1)	$	(163.2)	$	(164.9)


	December 31, 2021
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Gains (Losses) on Net Investment Hedges, Net of Tax		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2020	$	1.4	$	(179.0)	$	(8.5)	$	(66.3)	$	(46.6)	$	(299.0)
Other comprehensive income (loss) before reclassifications	(6.6)		178.2		33.4		21.5		(92.4)		134.1
Amounts reclassified from AOCI	3.0		54.6		0.6		—		—		58.2
Net current period other comprehensive income (loss)	(3.6)		232.8		34.0		21.5		(92.4)		192.3
Balance, December 31, 2021	$	(2.2)	$	53.8	$	25.5	$	(44.8)	$	(139.0)	$	(106.7)

The following table summarizes the amounts reclassified from AOCI:


(In millions)	Amounts Reclassified from AOCI						Income Statement Location
	For the Years Ended December 31,
	2023		2022		2021
Gains (losses) on securities available for sale	$	(17.0)	$	(12.6)	$	(3.8)	Other (income) expense
	3.6		2.6		0.8		Income tax (benefit) expense

Gains (losses) on cash flow hedges	11.6		201.6		(60.0)		Revenue
	3.7		(5.5)		(0.8)		Operating expense
	(0.3)		(0.3)		0.2		Other (income) expense
	(1.7)		(19.8)		6.0		Income tax (benefit) expense

Gains (losses) on net investment hedges(1)	—		38.1		(0.6)		Other (income) expense

Currency translation adjustments	—		(58.9)		—		Other (income) expense

Total reclassifications, net of tax	$	(0.1)	$	145.2	$	(58.2)

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
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+ Details

Leases - Operating Lease Liability Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 106.2
2025	96.1
2026	83.5
2027	86.1
2028	49.4
Thereafter	170.4
Total lease payments	591.7
Less: interest	101.4
Present value of operating lease liabilities	$ 490.3	$ 430.2

Financial Instruments - Summary of Financial Assets with Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	$ 610.7	$ 2,847.6
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	0.0	177.2
Overnight reverse repurchase agreements
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	0.0	59.0
Money market funds
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	610.7	2,581.5
Short-term debt securities
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	$ 0.0	$ 29.9

Collaborative and Other Relationships - Alkermes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Inventory and purchase commitment charges	$ 2,533.4	$ 2,278.3	$ 2,109.7
VUMERITY \| Alkermes
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration	15.00%
Royalties payable period, post FDA approval	5 years
Inventory and purchase commitment charges	$ 87.4	$ 83.0	$ 61.6

Property, Plant and Equipment - Components of property, plant, and equipment, net (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Land	$ 202.4		$ 202.4
Buildings	1,601.3		1,592.9
Leasehold improvements	135.7		107.7
Machinery and equipment	1,703.8		1,611.5
Computer software and hardware	1,032.1		999.9
Furniture and fixtures	61.5		61.1
Construction in progress	975.4		888.8
Total cost	5,712.2		5,464.3
Less: accumulated depreciation	(2,402.5)		(2,165.7)
Total property, plant and equipment, net	$ 3,309.7		$ 3,298.6
125 Broadway Building
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		$ 79.2
125 Broadway Building \| Buildings
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		72.6
125 Broadway Building \| Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		1.6
125 Broadway Building \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		$ 5.0

Financial Instruments - Summary of Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Marketable debt securities:
Amortized Cost		$ 2,199.1
Gross Unrealized Gains		0.3
Gross Unrealized Losses		(20.2)
Fair Value		2,179.2
Marketable equity securities:
Amortized Cost	$ 979.9	1,133.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(563.1)	(342.7)
Fair Value	416.8	791.1
Corporate debt securities Current
Marketable debt securities:
Amortized Cost		936.2
Gross Unrealized Gains		0.0
Gross Unrealized Losses		(4.9)
Fair Value		931.3
Corporate debt securities Non-current
Marketable debt securities:
Amortized Cost		305.3
Gross Unrealized Gains		0.1
Gross Unrealized Losses		(5.1)
Fair Value		300.3
Government securities Current
Marketable debt securities:
Amortized Cost		547.1
Gross Unrealized Gains		0.1
Gross Unrealized Losses		(5.0)
Fair Value		542.2
Government securities Non-current
Marketable debt securities:
Amortized Cost		271.4
Gross Unrealized Gains		0.0
Gross Unrealized Losses		(3.3)
Fair Value		268.1
Mortgage and other asset backed securities Current
Marketable debt securities:
Amortized Cost		0.0
Gross Unrealized Gains		0.0
Gross Unrealized Losses		0.0
Fair Value		0.0
Mortgage and other asset backed securities Non-current
Marketable debt securities:
Amortized Cost		139.1
Gross Unrealized Gains		0.1
Gross Unrealized Losses		(1.9)
Fair Value		137.3
Marketable equity securities, current
Marketable equity securities:
Amortized Cost	31.6
Gross Unrealized Gains	0.0
Gross Unrealized Losses	(21.0)
Fair Value	10.6
Marketable equity securities, non-current
Marketable equity securities:
Amortized Cost	948.3	1,133.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(542.1)	(342.7)
Fair Value	$ 406.2	$ 791.1

Share-Based Payments

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Share-Based Payments


Note 16:			Share-Based Payments

Share-Based Compensation Expense

The following table summarizes share-based compensation expense included in our consolidated statements of income:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Research and development	$	296.7	$	98.5	$	89.3
Selling, general and administrative	371.7		175.1		169.5
Subtotal	668.4		273.6		258.8
Capitalized share-based compensation costs	(10.2)		(9.3)		(8.0)
Share-based compensation expense included in total cost and expense	658.2		264.3		250.8
Income tax effect	(132.6)		(49.2)		(46.7)
Share-based compensation expense included in net income attributable to Biogen Inc.	$	525.6	$	215.1	$	204.1

In connection with our acquisition of Reata in September 2023 we recognized Reata equity-based compensation expense, inclusive of employer taxes, of approximately $393.4 million attributable to the post-acquisition service period, of which $196.4 million was recognized as a charge to selling, general and administrative expense with the remaining $197.0 million as a charge to research and development expense within our consolidated statements of income for the year ended December 31, 2023. These amounts were associated with the accelerated vesting of stock options and RSUs previously granted to Reata employees that required no future services to vest. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

The following table summarizes share-based compensation expense associated with each of our share-based compensation programs:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Market stock units	$	4.9	$	13.2	$	45.6
Time-vested restricted stock units	220.0		202.3		159.8
Performance stock units settled in stock	35.5		35.0		23.9
Performance stock units settled in cash	6.8		10.1		12.2
Employee stock purchase plan	10.5		12.7		17.3
Stock options	3.7		0.3		—
Reata equity awards(1)	387.0		—		—
Subtotal	668.4		273.6		258.8
Capitalized share-based compensation costs	(10.2)		(9.3)		(8.0)
Share-based compensation expense included in total cost and expense	$	658.2	$	264.3	$	250.8

As of December 31, 2023, unrecognized compensation cost related to unvested share-based compensation was approximately $287.4 million, net of estimated forfeitures. We expect to recognize the cost of these unvested awards over a weighted-average period of 1.8 years.

Share-Based Compensation Plans

We have three share-based compensation plans pursuant to which awards are currently being made: (i) the Biogen Inc. 2006 Non-Employee Directors Equity Plan (2006 Directors Plan); (ii) the Biogen Inc. 2017 Omnibus Equity Plan (2017 Omnibus Equity Plan); and (iii) the Biogen Inc. 2015 Employee Stock Purchase Plan (2015 ESPP).

Directors Plan

In May 2006 our shareholders approved the 2006 Directors Plan for share-based awards to our directors. Awards granted from the 2006 Directors Plan may include stock options, shares of restricted stock, RSUs, stock appreciation rights and other awards in such amounts and with such terms and conditions as may be determined by a committee of our Board of Directors, subject to the provisions of the 2006 Directors Plan. We have reserved a total of 1.6 million shares of common stock for issuance under the 2006 Directors Plan. The 2006 Directors Plan provides that awards other than stock options and stock appreciation rights will be counted against the total number of shares reserved under the plan in a 1.5-to-1 ratio. In June 2015 our shareholders approved an amendment to extend the term of the 2006 Directors Plan until June 2025.

Omnibus Plan

In June 2017 our shareholders approved the 2017 Omnibus Equity Plan for share-based awards to our employees. Awards granted from the 2017 Omnibus Equity Plan may include stock options, shares of restricted stock, RSUs, performance shares, stock appreciation rights and other awards in such amounts and with such terms and conditions as may be determined by a committee of our Board of Directors, subject to the provisions of the 2017 Omnibus Equity Plan. Shares of common stock available for grant under the 2017 Omnibus Equity Plan consist of 8.0 million shares reserved for this purpose, plus shares of common stock that remained available for grant under the Biogen Idec Inc. 2008 Omnibus Equity Plan (2008 Omnibus Equity Plan) as of June 7, 2017, or that could again become available for grant if outstanding awards under the 2008 Omnibus Equity Plan as of June 7, 2017, are cancelled, surrendered or terminated in whole or in part. The 2017 Omnibus Equity Plan provides that awards other than stock options and stock appreciation rights will be counted against the total number of shares available under the plan in a 1.5-to-1 ratio.

We have not made any awards pursuant to the 2008 Omnibus Equity Plan since our shareholders approved the 2017 Omnibus Equity Plan, and do not intend to make any awards pursuant to the 2008 Omnibus Equity Plan in the future, except that unused shares under the 2008 Omnibus Equity Plan have been carried over for use under the 2017 Omnibus Equity Plan.

Stock Options

In 2022 we granted approximately 81,000 stock options to our CEO (2022 CEO Grant) under the 2017 Omnibus Plan with a grant date fair value of $139.10 per option for a total of approximately $11.2 million. The fair value of the stock option grant is estimated as of the date of grant using a Black-Scholes option valuation model. The estimated fair value of the stock option is then expensed over the options' vesting periods. The 2022 CEO Grant is eligible to vest in equal annual installments over a three-year period from the grant date, subject to the CEO’s continued employment. The outstanding stock option has a 10-year term and is exercisable at a price per share not less than the fair market value of the underlying common stock on the date of grant.


	December 31, 2023
	Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at December 31, 2022	81,000	$	301.85	9.9 years
Granted	—	—
Exercised	—	—
Forfeited	—	—
Outstanding at December 31, 2023	81,000	$	301.85	8.9 years
Exercisable at December 31, 2023	27,000	$	301.85	8.9 years

Market Stock Units

MSUs awarded to employees prior to 2014 vested in four equal annual increments beginning on the first anniversary of the grant date. Participants may ultimately earn between zero and 150.0% of the target number of units granted based on actual stock performance.

MSUs awarded to employees in 2014 and thereafter vest in three equal annual increments beginning on the first anniversary of the grant date, and participants may ultimately earn between zero and 200.0% of the target number of units granted based on actual stock performance.

The vesting of these awards is subject to the respective employee’s continued employment. The number of MSUs granted represents the target number of units that are eligible to be earned based on the attainment of certain market-based criteria involving our stock price. The number of MSUs earned is calculated at each annual anniversary from the date of grant over the respective vesting periods, resulting in multiple performance periods. Accordingly, additional MSUs may be issued or currently outstanding MSUs may be cancelled upon final determination of the number of awards earned.

Beginning in 2022 we no longer grant MSUs as part of our long term incentive program and have replaced with granting performance-vested RSUs. MSUs granted in 2021 had a weighted average grant date fair value of $358.77.

The following table summarizes our MSU activity:


	December 31, 2023
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2022	113,000	$	366.52
Granted	—	—
Vested	(74,000)	368.87
Forfeited	(5,000)	372.87
Unvested at December 31, 2023	34,000	$	359.77

We value grants of MSUs using a lattice model with a Monte Carlo simulation. This valuation methodology utilizes several key assumptions, the 30 calendar day average closing stock price on the date of grant for MSUs, expected volatility of our stock price, risk-free rates of return and expected dividend yield.

The assumptions used in our valuation are summarized as follows:


												December 31, 2021
Expected dividend yield												—%
Range of expected stock price volatility												54.8% - 61.6%
Range of risk-free interest rates												0.06% - 0.21%
30 calendar day average stock price on grant date												$262.23 - $360.31
Weighted-average per share grant date fair value												$358.77

The fair values of MSUs vested in 2023, 2022 and 2021 totaled $20.7 million, $18.8 million and $22.5 million, respectively.

Performance Stock Units

PSUs Settled in Stock

During the first quarter of 2018 we began granting awards for performance-vested RSUs that will settle in stock. PSUs awarded to employees have a three-year performance period and vest on the third anniversary of the grant date. The vesting of these awards is subject to the respective employee’s continued employment. The number of PSUs granted represents the target number of units that are eligible to be earned based on the achievement of cumulative three-year performance measures established at the beginning of the performance period, which ends on December 31 of the third year of the performance period.

Beginning in 2022 we no longer grant MSUs as part of long term incentive program and have replaced with granting PSUs with a performance metric based on a three-year cumulative relative total shareholder return (rTSR) metric. The PSUs will vest on the third anniversary of the date of grant, with the number of PSUs earned based on this cumulative rTSR metric.

The following table summarizes our PSUs that settle in stock activity:


	December 31, 2023
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2022	336,000	$	292.95
Granted (1)	206,000	383.61
Vested	(100,000)	290.72
Forfeited	(53,000)	323.52
Unvested at December 31, 2023	389,000	$	325.73

PSUs settled in stock granted in 2022 and 2021 had weighted average grant date fair values of $294.43 and $276.61, respectively.

We value grants of PSUs using a lattice model with a Monte Carlo simulation. This valuation methodology utilizes several key assumptions, the 30 calendar day average closing stock price on the date of grant for PSUs, expected volatility of our stock price, risk-free rates of return and expected dividend yield.

The assumptions used in our valuation are summarized as follows:


	For the Years Ended December 31,
	2023	2022
Expected dividend yield	—%	—%
Range of expected stock price volatility	44.7%	44.0% - 45.9%
Range of risk-free interest rates	4.1%	1.8% - 3.9%
30 calendar day average stock price on grant date	$283.93	$231.31 - $294.86
Weighted-average per share grant date fair value	$383.61	$294.43

The fair values of PSUs settled in stock that vested in 2023, 2022 and 2021 totaled $28.6 million, $9.5 million and $15.5 million, respectively.

PSUs Settled in Cash

During the first quarter of 2018 we began granting awards for performance-vested restricted stock units that will settle in cash. PSUs awarded to employees have three performance periods and vest on the third anniversary of the grant date. The vesting of these awards is subject to the respective employee’s continued employment. The number of PSUs granted represents the target number of units that are eligible to be earned based on the achievement of three annual performance measures established when the performance objectives are defined, which will be at the beginning of each year and will end on December 31 of such year.

Participants may ultimately earn between zero and 200.0% of the target number of PSUs granted based on the degree of achievement of the applicable performance metric. Accordingly, additional PSUs may be issued or currently outstanding PSUs may be cancelled upon final determination of the number of units earned. PSUs are classified as liability awards and will be settled in cash based on the 30 calendar day average closing stock price through the vesting date, once the actual vested and earned number of PSUs is determined. Since no shares are issued, these awards do not dilute equity.

Beginning in 2022 we no longer grant this type of PSUs as part of our long term incentive program and have replaced with granting time-vested RSUs.

The following table summarizes our PSUs that settle in cash activity:


			December 31, 2023
			Shares
Unvested at December 31, 2022			83,000
Granted(1)			5,000
Vested			(41,000)
Forfeited			(6,000)
Unvested at December 31, 2023			41,000

The fair values of PSUs settled in cash that vested in 2023, 2022 and 2021 totaled $11.7 million, $11.0 million and $9.9 million, respectively.

Time-Vested Restricted Stock Units

RSUs awarded to employees generally vest no sooner than one-third per year over three years on the anniversary of the date of grant, or upon the third anniversary of the date of the grant, provided the employee remains continuously employed with us, except as otherwise provided in the plan. Shares of our common stock will be delivered to the employee upon vesting, subject to payment of applicable withholding taxes. RSUs awarded to directors for service on our Board of Directors vest on the first anniversary of the date of grant, provided in each case that the director continues to serve on our Board of Directors through the vesting date. Shares of our common stock will be delivered to the director upon vesting and are not subject to any withholding taxes.

The following table summarizes our RSU activity:


	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2022	1,946,000	$	237.90
Granted (1)	1,171,000	282.92
Vested	(822,000)	249.12
Forfeited	(439,000)	257.66
Unvested at December 31, 2023	1,856,000	$	256.74

RSUs granted in 2022 and 2021 had weighted average grant date fair values of $221.28 and $276.90, respectively.

The fair values of RSUs vested in 2023, 2022 and 2021 totaled $232.1 million, $116.3 million and $132.2 million, respectively.

Employee Stock Purchase Plan

In June 2015 our shareholders approved the 2015 ESPP. The maximum aggregate number of shares of our common stock that may be purchased under the 2015 ESPP is 6.2 million.

The following table summarizes our ESPP activity:


	For the Years Ended December 31,
(In millions, except share amounts)	2023		2022		2021
Shares issued under the 2015 ESPP	199,000		241,000		248,000
Cash received under the 2015 ESPP	$	45.1	$	44.2	$	54.4

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Allowance for credit loss, current	$ 2.4	$ 2.3
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, par value (in dollars per share)	$ 0.0005	$ 0.0005
Treasury stock at cost, shares (in shares)	23.8	23.8

Revenue - Total Reserves for Discounts and Allowances (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	$ 1,062.0	$ 1,035.0	$ 935.3	$ 1,276.0
Reduction of accounts receivable
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	135.5	143.4
Component of accrued expense and other
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	$ 926.5	$ 891.6

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues	$ 9,835.6	$ 10,173.4	$ 10,981.7
Cost and expense:
Cost of sales, excluding amortization and impairment of acquired intangible assets	2,533.4	2,278.3	2,109.7
Research and development	2,462.0	2,231.1	2,501.2
Selling, general and administrative	2,549.7	2,403.6	2,674.3
Amortization and impairment of acquired intangible assets	240.6	365.9	881.3
Collaboration profit sharing/(loss reimbursement)	218.8	(7.4)	7.2
(Gain) loss on fair value remeasurement of contingent consideration	0.0	(209.1)	(50.7)
Acquired in-process research and development	0.0	0.0	18.0
Restructuring charges	218.8	131.1	0.0
Gain on sale of building	0.0	(503.7)	0.0
Other (income) expense, net	315.5	(108.2)	1,095.5
Total cost and expense	8,538.8	6,581.6	9,236.5
Income before income tax (benefit) expense and equity in loss of investee, net of tax	1,296.8	3,591.8	1,745.2
Income tax (benefit) expense	135.3	632.8	52.5
Equity in (income) loss of investee, net of tax	0.0	(2.6)	(34.9)
Net income	1,161.5	2,961.6	1,727.6
Net income (loss) attributable to noncontrolling interests, net of tax	0.4	(85.3)	171.5
Net income attributable to Biogen Inc.	$ 1,161.1	$ 3,046.9	$ 1,556.1
Net income per share:
Basic earnings per share attributable to Biogen Inc. (in dollars per share)	$ 8.02	$ 20.96	$ 10.44
Diluted earnings per share attributable to Biogen Inc. (in dollars per share)	$ 7.97	$ 20.87	$ 10.40
Weighted-average shares used in calculating:
Weighted average number of common shares outstanding (in shares)	144,700	145,300	149,100
Diluted earnings per share attributable to Biogen Inc. (in shares)	145,600	146,000	149,600
Product revenue, net
Revenues	$ 7,246.7	$ 7,987.8	$ 8,846.9
Revenue from anti-CD20 therapeutic programs
Revenues	1,689.6	1,700.5	1,658.5
Contract manufacturing, royalty and other revenue
Revenues	$ 899.3	$ 485.1	$ 476.3

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment


Note 11:			Property, Plant and Equipment

Property, plant and equipment are recorded at historical cost, net of accumulated depreciation. Components of property, plant and equipment, net are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Land	$	202.4	$	202.4
Buildings	1,601.3		1,592.9
Leasehold improvements	135.7		107.7
Machinery and equipment	1,703.8		1,611.5
Computer software and hardware	1,032.1		999.9
Furniture and fixtures	61.5		61.1
Construction in progress	975.4		888.8
Total cost	5,712.2		5,464.3
Less: accumulated depreciation	(2,402.5)		(2,165.7)
Total property, plant and equipment, net	$	3,309.7	$	3,298.6

Depreciation expense totaled $254.2 million, $272.4 million and $235.3 million for the years ended December 31, 2023, 2022 and 2021, respectively.

For the years ended December 31, 2023, 2022 and 2021, we capitalized interest costs related to construction in progress totaling approximately $21.7 million, $17.1 million and $36.3 million, respectively.

Solothurn, Switzerland Manufacturing Facility

In order to support our future growth and drug development pipeline, we built a large-scale biologics manufacturing facility in Solothurn, Switzerland. This facility includes 393,000 square feet related to a large-scale biologics manufacturing facility, 290,000 square feet of warehouse, utilities and support space and 51,000 square feet of administrative space. As of December 31, 2023 and 2022, we had approximately $728.8 million and $711.1 million, respectively, capitalized as construction in progress related to this facility. In the second quarter of 2021 a portion of this facility (the first manufacturing suite) received a GMP multi-product license from the SWISSMEDIC, resulting in approximately $1.2 billion of fixed assets being placed into service during the second quarter of 2021. The second manufacturing suite became operational in January 2024, resulting in approximately $710.7 million of fixed assets being placed into service during the first quarter of 2024. Solothurn has been approved for the manufacture of ADUHELM and LEQEMBI by the FDA.

125 Broadway Building Sale

In September 2022 we completed the sale of our building and land parcel located at 125 Broadway for an aggregate sales price of approximately $603.0 million, which is inclusive of a $10.8 million tenant allowance. This sale resulted in a pre-tax gain on sale of approximately $503.7 million, net of transaction costs, which is reflected within gain on sale of building in our consolidated statements of income for the year ended December 31, 2022. This transaction included approximately $79.2 million of property, plant and equipment, net, which comprised of approximately $72.6 million for buildings, approximately $1.6 million for land and approximately $5.0 million for machinery and equipment.

Equity - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Mar. 31, 2022	Feb. 29, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income tax (benefit) expense	$ 135.3	$ 632.8	$ 52.5
Revenue	9,835.6	10,173.4	10,981.7
Net income attributable to Biogen Inc.	1,161.1	3,046.9	1,556.1
Samsung Bioepis
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income tax (benefit) expense		31.2
Ownership percentage				49.90%	15.00%
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income attributable to Biogen Inc.	(0.1)	145.2	(58.2)
Gains (losses) on securities available for sale \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	(17.0)	(12.6)	(3.8)
Income tax (benefit) expense	3.6	2.6	0.8
Gains (losses) on cash flow hedges \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	(0.3)	(0.3)	0.2
Income tax (benefit) expense	(1.7)	(19.8)	6.0
Revenue	11.6	201.6	(60.0)
Operating expense	3.7	(5.5)	(0.8)
Gains (losses) on net investment hedges(1) \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	0.0	38.1	(0.6)
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	$ 0.0	$ (58.9)	$ 0.0

Share-Based Payments - Shares Issued Under Employee Stock Purchase Plan (Details) - USD ($) shares in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under the 2015 ESPP (in shares)	6,200
2015 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under the 2015 ESPP (in shares)		199	241	248
Cash received under the 2015 ESPP		$ 45.1	$ 44.2	$ 54.4

Derivative Instruments - Summary of the Effect of Derivatives Designated as Net Investment Hedging Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Mar. 31, 2022	Feb. 29, 2012
Samsung Bioepis
Derivative Instruments, Gain (Loss) [Line Items]
Ownership percentage			49.90%	15.00%
Net investment hedge
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion) (in millions)	$ 20.4	$ 46.0
Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions)	(3.2)	(3.2)
Net investment hedge \| Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)	$ (4.6)	$ (0.6)

Indebtedness - Total Debt Maturities (Details) $ in Millions	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
2024	$ 150.0
2025	1,750.0
2026	500.0
2027	0.0
2028	0.0
2029 and thereafter	4,817.3
Notes payable and term loan	7,217.3
Less: debt discount and issuance fees	(279.1)
Notes payable and term loan	$ 6,938.2

Intangible Assets and Goodwill

12 Months Ended

Dec. 31, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets and Goodwill


Note 7:			Intangible Assets and Goodwill

Intangible Assets

Intangible assets, net of accumulated amortization, impairment charges and adjustments are summarized as follows:


		As of December 31, 2023						As of December 31, 2022
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology
Acquired and in-licensed rights and patents	2-22 years	$	8,180.2	$	(2,440.7)	$	5,739.5	$	3,866.6	$	(2,219.1)	$	1,647.5
Developed technology and other	13-31 years	3,548.6		(3,429.1)		119.5		3,548.7		(3,410.1)		138.6

Total completed technology		11,728.8		(5,869.8)		5,859.0		7,415.3		(5,629.2)		1,786.1
In-process research and development	Indefinite until commercialization	2,340.0		—		2,340.0		—		—		—
Priority review voucher	Indefinite	100.0		—		100.0		—		—		—
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	14,232.8	$	(5,869.8)	$	8,363.0	$	7,479.3	$	(5,629.2)	$	1,850.1

Amortization and Impairments

Amortization and impairment of acquired intangible assets totaled $240.6 million, $365.9 million and $881.3 million for the years ended December 31, 2023, 2022 and 2021, respectively. For the year ended December 31, 2023, we had no impairment charges.

Amortization of acquired intangible assets, excluding impairment charges, totaled $240.6 million, $246.3 million and $252.0 million for the years ended December 31, 2023, 2022 and 2021, respectively. The decrease in amortization of acquired intangible assets, excluding impairment charges, over the three years was primarily due to a lower rate of amortization for acquired intangible assets.

For the year ended December 31, 2022, amortization and impairment of acquired intangible assets reflects the impact of a $119.6 million impairment charge related to vixotrigine (BIIB074) for the potential treatment of DPN.

For the year ended December 31, 2021, amortization and impairment of acquired intangible assets reflects the impact of a $365.0 million impairment charge related to BIIB111 (timrepigene emparvovec), a $220.0 million impairment charge related to BIIB112 (cotoretigene toliparvovec) and a $44.3 million impairment charge related to vixotrigine for the potential treatment of TGN.

We monitor events and expectations regarding product performance. If new information indicates that the assumptions underlying our most recent analysis are substantially different than those utilized in our current estimates, our analysis would be updated and may result in a significant change in the anticipated lifetime revenue of the relevant products. The occurrence of an adverse event could substantially increase the amount of amortization expense related to our acquired intangible assets as compared to previous periods or our current expectations, which may result in a significant negative impact on our future results of operations.

Completed Technology

Completed technology primarily relates to our other marketed products and programs acquired through asset acquisitions, licenses and business combinations. Completed technology intangible assets are amortized over their estimated useful lives, which range between 2 to 31 years, with a remaining weighted average useful life of 12 years for acquired and in-licensed rights and patents and 10 years for developed technology and other. In connection with our acquisition of Reata in September 2023 we acquired SKYCLARYS, a commercially-approved product in the U.S., with an estimated fair value of approximately $4.2 billion, which includes measurement period adjustments.

IPR&D Related to Business Combinations

IPR&D represents the fair value assigned to research and development assets that we acquired as part of a business combination and had not yet reached technological feasibility at the date of acquisition. Included in IPR&D balances are adjustments related to foreign currency exchange rate fluctuations. We review amounts capitalized as

acquired IPR&D for impairment annually, as of October 31, and whenever events or changes in circumstances indicate to us that the carrying value of the assets might not be recoverable. The carrying value associated with our IPR&D assets as of December 31, 2023, relates to the IPR&D programs we acquired in connection with our acquisition of Reata in September 2023 with an estimated fair value of approximately $2.3 billion, which includes measurement period adjustments.

Priority Review Voucher

In connection with our acquisition of Reata in September 2023 we acquired a rare pediatric disease priority review voucher that may be used to obtain priority review by the FDA for a future regulatory submission or sold to a third party. We recorded the priority review voucher based on its estimated fair value of $100.0 million as an intangible asset. The estimated fair value was based on recent external purchase and sale transactions of similar vouchers.

For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

Vixotrigine

In connection with our acquisition of Convergence, we recognized $424.6 million of acquired IPR&D intangible assets for vixotrigine. In the periods following our acquisition of vixotrigine, there were numerous delays in the initiation of Phase 3 studies for the potential treatment of TGN and for the potential treatment of DPN, another form of neuropathic pain. We engaged with the FDA regarding the design of the potential Phase 3 studies of vixotrigine for the potential treatment of TGN and DPN and performed an additional clinical trial of vixotrigine, which was completed during 2022.

The performance of this additional clinical trial delayed the initiation of the Phase 3 studies of vixotrigine for the potential treatment of TGN, and, as a result, we recognized an impairment charge of $44.3 million related to vixotrigine for the potential treatment of TGN during the first quarter of 2021.

During the fourth quarter of 2022 we discontinued further development of vixotrigine based on regulatory, development and commercialization challenges. For the year ended December 31, 2022, we recognized an impairment charge of approximately $119.6 million related to vixotrigine for the potential treatment of DPN, reducing the remaining book value of this IPR&D intangible asset to zero. We also adjusted the value of our contingent consideration obligations related to this asset resulting in a pre-tax gain of approximately $209.1 million, which was recognized in (gain) loss on fair value remeasurement of contingent consideration within our consolidated statements of income for the year ended December 31, 2022.

BIIB111 and BIIB112

In connection with our acquisition of Nightstar Therapeutics plc, we recognized $480.0 million and $220.0 million of acquired IPR&D intangible assets for BIIB111 and BIIB112, respectively. During the second quarter of 2021 we announced that our Phase 3 STAR study of BIIB111 and our Phase 2/3 XIRIUS study of BIIB112 did not meet their primary endpoints. In the third quarter of 2021 we suspended further development on these programs based on the decision by management as part of its strategic review process. For the year ended December 31, 2021, we recognized an impairment charge of $365.0 million related to BIIB111 and an impairment charge of $220.0 million related to BIIB112, reducing the remaining book values of these IPR&D intangible assets to zero.

In addition, as a result of our decision to suspend further development of BIIB111 and BIIB112, we recorded charges of approximately $39.1 million during the third quarter of 2021 related to our manufacturing arrangements and other costs that we expect to incur as a result of suspending these programs. These charges were recognized in research and development expense in our consolidated statements of income for the year ended December 31, 2021.

Estimated Future Amortization of Intangible Assets

The estimated future amortization of finite-lived intangible assets for the next five years is expected to be as follows:


(In millions)	As of December 31, 2023
2024	$	345.0
2025	470.0
2026	485.0
2027	480.0
2028	495.0

Goodwill

The following table provides a roll forward of the changes in our goodwill balance:


	As of December 31,
(In millions)	2023		2022
Goodwill, beginning of year	$	5,749.0	$	5,761.1
Goodwill resulting from Reata acquisition	464.5		—

Other	5.7		(12.1)
Goodwill, end of year	$	6,219.2	$	5,749.0

For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

As of December 31, 2023 and 2022, we had no accumulated impairment losses related to goodwill. Other includes adjustments related to foreign currency exchange rate fluctuations.

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Firm ID	238
Auditor Location	Boston, Massachusetts
Auditor Name	PricewaterhouseCoopers LLP

Revenue - Other Revenues (Details) - USD ($) $ in Millions	12 Months Ended
Revenue - Other Revenues (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total product revenue	$ 9,835.6	$ 10,173.4	$ 10,981.7
Contract manufacturing revenue
Disaggregation of Revenue [Line Items]
Total product revenue	848.2	417.7	427.7
Royalty and other revenue
Disaggregation of Revenue [Line Items]
Total product revenue	51.1	67.4	48.6
Contract manufacturing, royalty and other revenue
Disaggregation of Revenue [Line Items]
Total product revenue	$ 899.3	$ 485.1	$ 476.3

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

+ Details

Collaborative and Other Relationships - Summary of Activity Related To Denali Therapeutics (Details) - Research and development - Denali Therapeutics - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 65.0	$ 75.1	$ 42.5
Expense reflected within statements of income	$ 39.0	$ 43.8	$ 25.5

Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Basic and diluted earnings per share

Basic and diluted shares outstanding used in our earnings per share calculation are calculated as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Numerator:
Net income attributable to Biogen Inc.	$	1,161.1	$	3,046.9	$	1,556.1
Denominator:
Weighted average number of common shares outstanding	144.7		145.3		149.1
Effect of dilutive securities:

Time-vested restricted stock units	0.7		0.5		0.3
Market stock units	—		0.1		0.1
Performance stock units settled in stock	0.2		0.1		0.1
Dilutive potential common shares	0.9		0.7		0.5
Shares used in calculating diluted earnings per share	145.6		146.0		149.6

Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) payment segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jul. 31, 2023	Apr. 30, 2022 USD ($)	Mar. 31, 2022	Feb. 29, 2012
Property, Plant and Equipment [Line Items]
Interest in subsidiary (less than given percentage)	100.00%
Number of operating segments \| segment	1
Number of reportable segment \| segment	1
Advertising costs	$ 71.4	$ 54.1	$ 98.7
LEQEMBI Collaboration
Property, Plant and Equipment [Line Items]
Share of non-controling interest recognized	50.00%			50.00%
Samsung Bioepis
Property, Plant and Equipment [Line Items]
Due from joint venture					$ 1,300.0
Number of payments \| payment	2
Samsung Bioepis \| Payment Due At First Anniversary
Property, Plant and Equipment [Line Items]
Due from joint venture					812.5
Samsung Bioepis \| Payment Due At Second Anniversary
Property, Plant and Equipment [Line Items]
Due from joint venture					$ 437.5
Samsung Bioepis
Property, Plant and Equipment [Line Items]
Ownership percentage						49.90%	15.00%
Minimum
Property, Plant and Equipment [Line Items]
Payment terms of accounts receivable arising from product sales	30 days
Minimum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Payment terms of accounts receivable arising from product sales	90 days
Maximum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years

Share-Based Payments - Share-based Compensation Expense Included in Consolidation Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ (274.4)	$ (263.5)	$ (246.6)
Subtotal	668.4	273.6	258.8
Capitalized share-based compensation costs	(10.2)	(9.3)	(8.0)
Share-based compensation expense included in total cost and expense	658.2	264.3	250.8
Income tax effect	(132.6)	(49.2)	(46.7)
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	296.7	98.5	89.3
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	371.7	175.1	169.5
Share-based compensation expense included in net income attributable to Biogen Inc.
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 525.6	$ 215.1	$ 204.1

Intangible Assets and Goodwill - Changes in Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Goodwill, beginning of year	$ 5,749.0	$ 5,761.1
Goodwill resulting from Reata acquisition	464.5	0.0
Other	5.7	(12.1)
Goodwill, end of year	$ 6,219.2	$ 5,749.0

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Components of property, plant and equipment, net


Asset Category			Useful Lives
Land			Not depreciated
Buildings			15 to 40 years
Leasehold Improvements			Lesser of the useful life or the term of the respective lease
Furniture and Fixtures			5 to 7 years
Machinery and Equipment			5 to 20 years
Computer Software and Hardware			3 to 5 years

Components of property, plant and equipment, net are summarized as follows:


	As of December 31,
(In millions)	2023		2022
Land	$	202.4	$	202.4
Buildings	1,601.3		1,592.9
Leasehold improvements	135.7		107.7
Machinery and equipment	1,703.8		1,611.5
Computer software and hardware	1,032.1		999.9
Furniture and fixtures	61.5		61.1
Construction in progress	975.4		888.8
Total cost	5,712.2		5,464.3
Less: accumulated depreciation	(2,402.5)		(2,165.7)
Total property, plant and equipment, net	$	3,309.7	$	3,298.6

Restructuring

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Restructuring


Note 4:			Restructuring

2023 Fit for Growth Restructuring Program

In 2023 we initiated additional cost saving measures as part of our Fit for Growth program to reduce operating costs, while improving operating efficiency and effectiveness. The Fit for Growth program is expected to generate approximately $1.0 billion in gross operating expense savings by 2025, some of which will be reinvested in various initiatives. The Fit for Growth program is currently estimated to include net headcount reductions of approximately 1,000 employees and we expect to incur restructuring charges ranging from approximately $260.0 million to $280.0 million.

Total charges incurred from our 2023 cost saving initiatives are summarized as follows:


	For the Year Ended December 31,
	2023
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total
Selling, general and administrative	$	—	$	23.3	$	23.3
Research and development	—		1.2		1.2
Restructuring charges	153.4		34.6		188.0
Total charges	$	153.4	$	59.1	$	212.5

Other Costs: includes costs associated with items such as asset abandonment and write-offs, facility closure costs, pretax gains and losses resulting from the termination of certain leases, employee non-severance expense, consulting fees and other costs.

Reata Integration

Following the close of our Reata acquisition, we implemented an integration plan designed to realize operating synergies through cost savings and avoidance. These amounts are primarily related to severance and are expected to be paid by the end of 2024. For the year ended December 31, 2023, we recognized approximately $30.4 million of net pre-tax restructuring charges related to employee severance costs.

2022 Cost Saving Initiatives

In December 2021 and May 2022 we announced our plans to implement a series of cost-reduction measures during 2022. These savings are being achieved through a number of initiatives, including reductions to our workforce, the substantial elimination of our commercial ADUHELM infrastructure, deprioritization of certain research and development programs, the consolidation of certain real estate locations and operating efficiencies across our selling, general and administrative and research and development functions. Charges related to our 2022 cost saving initiatives were substantially incurred during 2022 with remaining payments expected to be made through 2026.

Total charges incurred from our 2022 cost saving initiatives are summarized as follows:


	For the Years Ended December 31,
	2023						2022
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs(1)		Total
Restructuring charges	$	(2.2)	$	2.6	$	0.4	$	112.6	$	18.5	$	131.1
Total charges	$	(2.2)	$	2.6	$	0.4	$	112.6	$	18.5	$	131.1

Charges and spending related to our 2023 and 2022 workforce reductions and Reata integration are summarized as follows:


(In millions)	Total
Restructuring reserve, December 31, 2021	$	—
Expense	112.6
Payment	(78.0)
Foreign currency and other adjustments	1.3
Restructuring reserve, December 31, 2022	35.9
Expense	181.6
Payment	(140.5)
Foreign currency and other adjustments	(1.6)
Restructuring reserve, December 31, 2023	$	75.4

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies


Note 1:			Summary of Significant Accounting Policies

References in these notes to "Biogen," the "company," "we," "us" and "our" refer to Biogen Inc. and its consolidated subsidiaries.

Business Overview

Biogen is a global biopharmaceutical company focused on discovering, developing and delivering innovative therapies for people living with serious and complex diseases worldwide. We have a broad portfolio of medicines to treat MS, have introduced the first approved treatment for SMA, co-developed treatments to address a defining pathology of Alzheimer’s disease and launched the first approved treatment to target a genetic cause of ALS. Through our 2023 acquisition of Reata we market the first and only drug approved in the U.S. and the E.U. for the treatment of Friedreich's Ataxia in adults and adolescents aged 16 years and older. We are focused on advancing our pipeline in neurology, specialized immunology and rare diseases. We support our drug discovery and development efforts through internal research and development programs and external collaborations.

Our marketed products include TECFIDERA, VUMERITY, AVONEX, PLEGRIDY, TYSABRI and FAMPYRA for the treatment of MS; SPINRAZA for the treatment of SMA; SKYCLARYS for the treatment of Friedreich's Ataxia; QALSODY for the treatment of ALS; and FUMADERM for the treatment of severe plaque psoriasis.

We also have collaborations with Eisai on the commercialization of LEQEMBI for the treatment of Alzheimer's disease and Sage on the commercialization of ZURZUVAE for the treatment of PPD and we have certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, CLL and other conditions; RITUXAN HYCELA for the treatment of non-Hodgkin's lymphoma and CLL; GAZYVA for the treatment of CLL and follicular lymphoma; OCREVUS for the treatment of PPMS and RMS; LUNSUMIO for the treatment of relapsed or refractory follicular lymphoma; COLUMVI, a bispecific antibody for the treatment of non-Hodgkin's lymphoma; and have the option to add other potential anti-CD20 therapies, pursuant to our collaboration arrangements with Genentech, a wholly-owned member of the Roche Group.

We commercialize a portfolio of biosimilars of advanced biologics including BENEPALI, an etanercept biosimilar referencing ENBREL, IMRALDI, an adalimumab biosimilar referencing HUMIRA, and FLIXABI, an infliximab biosimilar referencing REMICADE, in certain countries in Europe, as well as BYOOVIZ, a ranibizumab biosimilar referencing LUCENTIS, in the U.S. and certain international markets. We also have exclusive rights to commercialize TOFIDENCE, a tocilizumab biosimilar referencing ACTEMRA. We continue to develop potential biosimilar product SB15, a proposed aflibercept biosimilar referencing EYLEA.

For additional information on our collaboration arrangements, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in this report.

Consolidation

Our consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and variable interest entities where we are the primary beneficiary. For consolidated entities where we own or are exposed to less than 100.0% of the economics, we record net income (loss) attributable to noncontrolling interests, net of tax in our consolidated statements of income equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties. Intercompany balances and transactions are eliminated in consolidation.

In determining whether we are the primary beneficiary of a variable interest entity, we apply a qualitative approach that determines whether we have both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to that entity. We continuously assess whether we are the primary beneficiary of a variable interest entity as changes to existing relationships or future transactions may result in us consolidating or deconsolidating one or more of our collaborators or partners. In November 2023 we terminated the Neurimmune Agreement, which resulted in the deconsolidation of our variable interest entity, Neurimmune.

Use of Estimates

The preparation of our consolidated financial statements requires us to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, equity, revenue and expense and related

disclosure of contingent assets and liabilities. On an ongoing basis we evaluate our estimates, judgments and assumptions. We base our estimates on historical experience and on various other assumptions that we believe are reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenue and expense. Actual results may differ from these estimates.

Revenue Recognition

We recognize revenue when our customer obtains control of promised goods or services, in an amount that reflects the consideration which we expect to receive in exchange for those goods or services. We recognize revenue following the five-step model prescribed under FASB ASC 606, Revenue from Contracts with Customers: (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy the performance obligations.

Product Revenue

In the U.S., we sell our products primarily to wholesale and specialty distributors and specialty pharmacies. In other countries, we sell our products primarily to wholesale distributors, hospitals, pharmacies and other third-party distribution partners. These customers subsequently resell our products to health care providers and patients. In addition, we enter into arrangements with health care providers and payors that provide for government-mandated or privately-negotiated discounts and allowances related to our products.

Product revenue is recognized when the customer obtains control of our product, which occurs at a point in time, typically upon delivery to the customer. We expense incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that we would have recognized is one year or less or the amount is immaterial.

Reserves for Discounts and Allowances

Product revenue is recorded net of reserves established for applicable discounts and allowances that are offered within contracts with our customers, health care providers or payors, including those associated with the implementation of pricing actions in certain of the international markets in which we operate.

Product revenue reserves, which are classified as a reduction in product revenue, are generally characterized in the following categories: discounts, contractual adjustments and returns.

These reserves are based on estimates of the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if the amount is payable to our customer) or a liability (if the amount is payable to a party other than our customer). Our estimates of reserves established for variable consideration are calculated based upon a consistent application of our methodology utilizing the expected value method. These estimates reflect our historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. The transaction price, which includes variable consideration reflecting the impact of discounts and allowances, may be subject to constraint and is included in the net sales price only to the extent that it is probable that a significant reversal of the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts may ultimately differ from our estimates. If actual results vary, we adjust these estimates, which could have an effect on earnings in the period of adjustment.

Discounts include trade term discounts and wholesaler incentives. Trade term discounts and wholesaler incentives primarily relate to estimated obligations for credits to be granted to wholesalers for remitting payment on their purchases within established incentive periods and credits to be granted to wholesalers for compliance with various contractually-defined inventory management practices, respectively. We determine these reserves based on our historical experience, including the timing of customer payments.

Contractual adjustments primarily relate to Medicaid and managed care rebates in the U.S., pharmacy rebates, co-payment (copay) assistance, VA and PHS discounts, specialty pharmacy program fees and other governmental rebates or applicable allowances.

•Medicaid rebates: relate to our estimated obligations to states under established reimbursement arrangements. Rebate accruals are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expense and other current liabilities in our consolidated balance sheets. Our liability for Medicaid rebates consists of estimates for claims

that a state will make for the current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, invoices received for claims from the prior quarters that have not been paid and an estimate of potential claims that will be made for inventory that exists in the distribution channel at period end.

•Governmental rebates: or chargebacks, including VA and PHS discounts, represent our estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices we charge to wholesalers which provide those products. The wholesaler charges us for the difference between what the wholesaler pays for the products and the ultimate selling price to the qualified healthcare providers. Rebate and chargeback reserves are established in the same period as the related revenue is recognized, resulting in a reduction of product revenue and a reduction in the net accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider from the wholesaler, and we generally issue credits for such amounts within a few weeks of the wholesaler notifying us about the resale. Our reserves for VA, PHS and other chargebacks consist of amounts for inventory that exists at the wholesalers that we expect will be sold to qualified healthcare providers and chargebacks that wholesalers have claimed for which we have not issued a credit.

•Managed care rebates: represent our estimated obligations to third-parties, primarily pharmacy benefit managers. Rebate accruals are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expense and other current liabilities in our consolidated balance sheets. These rebates result from performance-based goals, formulary position and price increase limit allowances (price protection). The calculation of the accrual for these rebates is based on an estimate of the coverage patterns and the resulting applicable contractual rebate rate(s) to be earned over a contractual period.

•Copay assistance: represents financial assistance to qualified patients, assisting them with prescription drug co-payments required by insurance. The calculation of the accrual for copay is based on an estimate of claims and the cost per claim that we expect to receive associated with inventory that exists in the distribution channel at period end.

•Pharmacy rebates: represent our estimated obligations resulting from contractual commitments to sell products to specific pharmacies. Rebate accruals are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expense and other current liabilities in our consolidated balance sheets. These rebates result from contracted discounts on product purchased or product dispensed. The calculation of the accrual for these rebates is based on an estimate of the pharmacy’s buying or dispensing patterns and the resulting applicable contractual rebate rate(s) to be earned over the contractual period.

•Other governmental rebates: non-U.S. pharmaceutical taxes or applicable allowances primarily relate to mandatory rebates and discounts in international markets where government-sponsored healthcare systems are the primary payors for healthcare.

Product return reserves are established for returns made by wholesalers and are recorded in the period the related revenue is recognized, resulting in a reduction to product revenue. In accordance with contractual terms, wholesalers are permitted to return product for reasons such as damaged or expired product. The majority of wholesaler returns are due to product expiration. Expired product return reserves are estimated through a comparison of historical return data to their related sales on a production lot basis. Historical rates of return are determined for each product and are adjusted for known or expected changes in the marketplace specific to each product.

In addition to discounts, rebates and product returns, we also maintain certain customer service contracts with distributors and other customers in the distribution channel that provide us with inventory management, data and distribution services, which are generally reflected as a reduction of revenue. To the extent we can demonstrate a separable benefit and fair value for these services we classify these payments in selling, general and administrative expense in our consolidated statements of income.

Revenue from Anti-CD20 Therapeutic Programs

Our collaboration with Genentech is within the scope of ASC 808, Collaborative Agreements, which provides guidance on the presentation and disclosure of collaborative arrangements. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.

Our share of the pre-tax co-promotion profits on RITUXAN, GAZYVA and LUNSUMIO and royalty revenue on sales of OCREVUS, resulted from an exchange of a license. As we do not have future performance obligations under the license or collaboration agreement, revenue is recognized as the underlying sales occur.

Revenue from anti-CD20 therapeutic programs consist of:

(i) our share of pre-tax profits and losses in the U.S. for RITUXAN, GAZYVA and LUNSUMIO;

(ii) royalty revenue on sales of OCREVUS; and

(ii) other revenue from anti-CD20 therapeutic programs, which consists of our share of pre-tax co-promotion profits on RITUXAN in Canada, royalties on net sales of COLUMVI in the U.S. and royalties on sales of LUNSUMIO outside the U.S.

Pre-tax co-promotion profits on RITUXAN, GAZYVA and LUNSUMIO are calculated and paid to us by Genentech and the Roche Group. Pre-tax co-promotion profits consist of net sales to third-party customers less applicable costs to manufacture, third-party royalty expense, distribution, selling and marketing expense and joint development expense incurred by Genentech and the Roche Group. Our share of the pre-tax profits on RITUXAN, GAZYVA and LUNSUMIO include estimates that are based on information received from Genentech and the Roche Group. These estimates are subject to change and actual results may differ.

We recognize royalty revenue on sales of OCREVUS based on our estimates from third party and market research data of OCREVUS sales occurring during the corresponding period. Differences between actual and estimated royalty revenue will be adjusted for in the period in which they become known, which is generally expected to be the following quarter.

Prior to regulatory approval, we record our share of the expense incurred by the collaboration for the development of anti-CD20 products within research and development expense and pre-commercialization costs within selling, general and administrative expense in our consolidated statements of income. After an anti-CD20 product is approved, we record our share of the development and sales and marketing expense related to that product as a reduction of our share of pre-tax profits in revenue from anti-CD20 therapeutic programs.

Accordingly, Biogen recorded its share of the expense incurred in connection with the development of LUNSUMIO within research and development expense and its share of pre-commercialization costs within selling, general and administrative expense through December 2022, when regulatory approval was granted by the FDA. Beginning in January 2023 our share of pre-tax profits and losses in the U.S. for LUNSUMIO was reflected as a component of revenue from anti-CD20 therapeutic programs within our consolidated statements of income.

For additional information on our relationship with Genentech, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Contract Manufacturing, Royalty and Other Revenue

Contract Manufacturing Revenue

We record contract manufacturing revenue primarily from amounts earned under contract manufacturing agreements with our strategic customers. Revenue under contract manufacturing agreements is recognized when the customer obtains control of the product, which may occur at a point in time or over time depending on the terms and conditions of the agreement. During the first quarter of 2023 we began recognizing contract manufacturing revenue for LEQEMBI, upon accelerated approval of LEQEMBI in the U.S. Prior to accelerated approval, our share of contract manufacturing amounts related to LEQEMBI were recognized in research and development expense within our consolidated statements of income.

Royalty and Other Revenue

Royalty and other revenue primarily reflects the royalties we receive from net sales on products related to patents that we have out-licensed, as well as royalty revenue on biosimilar products from our collaboration arrangements with Samsung Bioepis and our 50.0% share of LEQEMBI product revenue, net and cost of sales, including royalties, as we are not the principal. These arrangements resulted from an exchange of a license and utilize the sales and usage based royalty exception. Therefore, royalties received are recognized as the underlying sales occur.

Collaborative and Other Relationships

We also have a number of significant collaborative and other third-party relationships for revenue and for the development, regulatory approval, commercialization and marketing of certain of our products and product candidates. Where we are the principal on sales transactions with third parties, we recognize revenue, cost of sales and operating expense on a gross basis in their respective lines in our consolidated statements of income. Where we are not the principal on sales transactions with third parties, our share of the revenue, cost of sales and operating expense is recorded as a component of other revenue in our consolidated statements of income.

Our development and commercialization arrangements with Genentech, Eisai, Sage and Samsung Bioepis represent collaborative arrangements as each party is an active participant in one or more joint operating activities and is exposed to significant risks and rewards of these arrangements. These arrangements resulted from an exchange of a license and utilize the sales and usage based royalty exception, as applicable. Therefore, revenue relating to royalties or profit-sharing amounts received is recognized as the underlying sales occur.

For additional information on our collaboration arrangements with Genentech, Eisai, Sage and Samsung Bioepis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Fair Value Measurements

We have certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements.

•Level 1 — Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access;

•Level 2 — Fair values are determined by utilizing quoted prices for identical or similar assets and liabilities in active markets or other market observable inputs such as interest rates, yield curves, foreign currency spot rates and option pricing valuation models; and

•Level 3 — Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

The majority of our financial assets have been classified as Level 2. Our financial assets (which typically include our cash equivalents, marketable debt securities and certain of our marketable equity securities, derivative contracts and plan assets for deferred compensation) have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third-party pricing services or option pricing valuation models. The pricing services utilize industry standard valuation models, including both income and market-based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events.

We validate the prices provided by our third-party pricing services by understanding the models used, obtaining market values from other pricing sources and analyzing pricing data in certain instances. The option pricing valuation models use assumptions within the model, including the term, stock price volatility, constant maturity risk-free interest rate and dividend yield. After completing our validation procedures, we did not adjust or override any fair value measurements provided by our pricing services as of December 31, 2023 and 2022.

Other Assets and Liabilities

The carrying amounts reflected in our consolidated balance sheets for current accounts receivable, due from anti-CD20 therapeutic programs, other current assets, accounts payable and accrued expense and other, approximate fair value due to their short-term maturities.

Cash and Cash Equivalents

We consider only those investments that are highly liquid, readily convertible to cash and that mature within three months from date of purchase to be cash equivalents. As of December 31, 2023 and 2022, cash equivalents were comprised of money market funds, commercial paper, overnight reverse repurchase agreements and other debt securities with maturities less than three months from the date of purchase.

Accounts Receivable

The majority of our accounts receivable arise from product sales and primarily represent amounts due from our wholesale and other third-party distributors, public hospitals, pharmacies and other government entities and have standard payment terms that generally require payment within 30 to 90 days.

We do not adjust our receivables for the effects of a significant financing component at contract inception if we expect to collect the receivables in one year or less from the time of sale.

We provide reserves against accounts receivable for estimated losses that may result from a customer's inability to pay. Amounts determined to be uncollectible are charged or written-off against the reserve.

Receivables from Samsung BioLogics

In April 2022 we completed the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics, which resulted in a receivable of approximately $1.3 billion in cash to be deferred over two payments. The first deferred payment of $812.5 million was received in April 2023 and the second deferred payment of $437.5 million is due at the second anniversary of the closing of this transaction in April 2024. The payments due to us from Samsung BioLogics have been recorded at their estimated fair values through the use of risk-adjusted discount rates. For additional information on the accounting for the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

Concentration of Credit Risk

Financial instruments that potentially subject us to concentrations of credit risk include cash and cash equivalents, investments, derivatives and accounts receivable. We attempt to minimize the risks related to cash and cash equivalents and investments by investing in a broad and diverse range of financial instruments as previously defined by us. We have established guidelines related to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. Our investment portfolio is maintained in accordance with our investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. We minimize credit risk resulting from derivative instruments by choosing only highly rated financial institutions as counterparties.

Concentrations of credit risk with respect to receivables, which are typically unsecured, are somewhat mitigated due to the wide variety of customers and markets using our products, as well as their dispersion across many different geographic areas. We monitor the financial performance and creditworthiness of our customers so that we can properly assess and respond to changes in their credit profile. We continue to monitor these conditions and assess their possible impact on our business.

Marketable Securities and Other Investments

Marketable Debt Securities

Available-for-sale marketable debt securities are recorded at fair market value and unrealized gains and losses are included in AOCI in equity, net of related tax effects, unless the security has experienced a credit loss, we have determined that we have the intent to sell the security or we have determined that it is more likely than not that we will have to sell the security before its expected recovery. Realized gains and losses are reported in other (income) expense, net on a specific identification basis.

Marketable Equity Securities and Venture Capital Funds

Our marketable equity securities are recorded at fair market value and unrealized gains and losses are included in other (income) expense, net in our consolidated statements of income. Our marketable equity securities represent investments in publicly traded equity securities and are included in investments and other assets in our consolidated balance sheets.

Our investments in venture capital funds are recorded at net asset value, which approximates fair value, and unrealized gains and losses are included in other (income) expense, net in our consolidated statements of income.

The underlying investments of the venture capital funds in which we invest are in equity securities of certain biotechnology companies and are included in investments and other assets in our consolidated balance sheets.

Non-Marketable Equity Securities

We also invest in equity securities of companies whose securities are not publicly traded and where fair value is not readily available. These investments are recorded using either the equity method of accounting or the cost minus impairment adjusted for observable price changes, depending on our ownership percentage and other factors that suggest we have significant influence. We monitor these investments to evaluate whether any increase or decline in their value has occurred, based on the implied value of recent company financings, public market prices of comparable companies and general market conditions. These investments are included in investments and other assets in our consolidated balance sheets.

Evaluating Marketable Debt Securities for Other-than-Temporary Impairments

We conduct periodic reviews to identify and evaluate each investment that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. Unrealized losses on available-for-sale debt securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, in AOCI.

For available-for-sale debt securities with unrealized losses, management performs an analysis to assess whether we intend to sell or whether we would more likely than not be required to sell the security before the expected recovery of the amortized cost basis. Where we intend to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is reflected in earnings as an impairment loss.

Regardless of our intent to sell a security, we perform additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security.

Equity Method of Accounting

In circumstances where we have the ability to exercise significant influence over the operating and financial policies of a company in which we have an investment, we utilize the equity method of accounting for recording investment activity. In assessing whether we exercise significant influence, we consider the nature and magnitude of our investment, the voting and protective rights we hold, any participation in the governance of the other company and other relevant factors such as the presence of a collaborative or other business relationship. Under the equity method of accounting, we record in our consolidated statements of income our share of income or loss of the other company. If our share of losses exceeds the carrying value of our investment, we will suspend recognizing additional losses and will continue to do so unless we commit to providing additional funding.

Inventory

Inventories are stated at the lower of cost or net realizable value with cost based on the first-in, first-out method. We classify our inventory costs as long-term when we expect to utilize the inventory beyond our normal operating cycle and include these costs in investments and other assets in our consolidated balance sheets. Inventory that can be used in either the production of clinical or commercial products is expensed as research and development costs when identified for use in a clinical manufacturing campaign.

Capitalization of Inventory Costs

We capitalize inventory costs associated with our products prior to regulatory approval, when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. We consider numerous attributes in evaluating whether the costs to manufacture a particular product should be capitalized as an asset. We assess the regulatory approval process and where the particular product stands in relation to that approval process, including any known safety or efficacy concerns, potential labeling restrictions and other impediments to approval. We evaluate our anticipated research and development initiatives and constraints relating to the product and the indication in which it will be used. We consider our manufacturing environment including our supply chain in determining logistical constraints that could hamper approval or commercialization. We consider the shelf life of the product in relation to the expected timeline for approval and we consider patent related or contract issues that may prevent or delay commercialization. We also

base our judgment on the viability of commercialization, trends in the marketplace and market acceptance criteria. Finally, we consider the reimbursement strategies that may prevail with respect to the product and assess the economic benefit that we are likely to realize. We expense previously capitalized costs related to pre-approval inventory upon changes in such judgments, due to, among other potential factors, a denial or significant delay of approval by necessary regulatory bodies.

Obsolescence and Unmarketable Inventory

At each reporting period we review our inventories for excess or obsolescence and write-down obsolete or otherwise unmarketable inventory to its estimated net realizable value. If the actual net realizable value is less than that estimated by us, or if it is determined that inventory utilization will further diminish based on estimates of demand, additional inventory write-downs may be required. Additionally, our products are subject to strict quality control and monitoring that we perform throughout the manufacturing process. In the event that certain batches or units of product no longer meet quality specifications, we will record a charge to cost of sales to write-down any unmarketable inventory to its estimated net realizable value. In all cases, product inventory is carried at the lower of cost or its estimated net realizable value. Amounts written-down due to unmarketable inventory are charged to cost of sales in our consolidated statements of income.

Property, Plant and Equipment

Property, plant and equipment are carried at cost, subject to reviews for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The cost of normal, recurring or periodic repairs and maintenance activities related to property, plant and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits.

Interest costs incurred during the construction of major capital projects are capitalized until the underlying asset is ready for its intended use, at which point the interest costs are amortized as depreciation expense over the life of the underlying asset. We also capitalize certain direct and incremental costs associated with the validation effort required for licensing by regulatory agencies of new manufacturing equipment for the production of a commercially approved drug. These costs primarily include direct labor and material and are incurred in preparing the equipment for its intended use. The validation costs are either amortized over the life of the related equipment or expensed as cost of sales when the product produced in the validation process is sold.

In addition, we capitalize certain internal use computer software development costs. If the software is an integral part of production assets, these costs are included in machinery and equipment and are amortized on a straight-line basis over the estimated useful lives of the related software, which generally range from three to five years.


Asset Category			Useful Lives
Land			Not depreciated
Buildings			15 to 40 years
Leasehold Improvements			Lesser of the useful life or the term of the respective lease
Furniture and Fixtures			5 to 7 years
Machinery and Equipment			5 to 20 years
Computer Software and Hardware			3 to 5 years

When we dispose of property, plant and equipment, we remove the associated cost and accumulated depreciation from the related accounts in our consolidated balance sheets and include any resulting gain or loss in our consolidated statements of income.

Leases

We determine if an arrangement is a lease at contract inception. Operating lease assets represent our right to use an underlying asset for the lease term and operating lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, we include options to extend or terminate the lease when it is reasonably certain that they will be exercised.

We use the implicit rate when readily determinable and use our incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. Our incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease.

The lease payments used to determine our operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized in our operating lease assets in our consolidated balance sheets. Our lease agreements may include both lease and non-lease components, which we account for as a single lease component when the payments are fixed. Variable payments included in the lease agreement are expensed as incurred. For certain equipment leases, such as vehicles, we apply a portfolio approach to effectively account for the operating lease assets and liabilities.

Our operating leases are reflected in operating lease assets, accrued expense and other and long-term operating lease liabilities in our consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

We also have real estate lease agreements which are subleased to third-parties. Operating leases for which we are the sublessor are included in accrued expense and other and other long-term liabilities in our consolidated balance sheets. We recognize sublease income on a straight-line basis over the lease term in our consolidated statements of income.

For additional information on our leases, please read Note 12, Leases, to these consolidated financial statements.

Intangible Assets

Our intangible assets consist of completed technology (comprised of acquired and in-licensed rights and patents, developed technology and other), IPR&D acquired after January 1, 2009, priority review vouchers and trademarks and trade names. Our intangible assets are recorded at fair value at the time of their acquisition and are stated in our consolidated balance sheets net of accumulated amortization and impairments, if applicable.

Intangible assets related to acquired and in-licensed rights and patents, developed technology and other are amortized over their estimated useful lives using the economic consumption method if anticipated future revenue can be reasonably estimated. The straight-line method is used when revenue cannot be reasonably estimated. Amortization is recorded within amortization and impairment of acquired intangible assets in our consolidated statements of income.

We amortize the intangible assets related to our marketed products using the economic consumption method based on revenue generated from the products underlying the related intangible assets. An analysis of the anticipated lifetime revenue of our marketed products is performed annually during our long-range planning cycle and whenever events or changes in circumstances would significantly affect anticipated lifetime revenue of the relevant products.

Intangible assets related to trademarks, trade names, IPR&D prior to commercialization and priority review vouchers are not amortized because they have indefinite lives; however, they are subject to review for impairment. We review our intangible assets with indefinite lives for impairment annually, as of October 31, and whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable.

Acquired In-process Research and Development

Acquired IPR&D represents the fair value assigned to research and development assets that have not reached technological feasibility. The value assigned to acquired IPR&D is determined by estimating the costs to develop the acquired technology into commercially viable products, estimating the resulting revenue from the projects and discounting the net cash flow to present value. The revenue and cost projections used to value acquired IPR&D are, as applicable, reduced based on the probability of success of developing a new drug. Additionally, the projections consider the relevant market sizes and growth factors, expected trends in technology and the nature and expected timing of new product introductions by us and our competitors. The rates utilized to discount the net cash flow to present value are commensurate with the stage of development of the projects and uncertainties in the economic estimates used in the projections. Upon the acquisition of IPR&D, we complete an assessment of whether our acquisition constitutes the purchase of a single asset or a group of assets. We consider multiple factors in this assessment, including the nature of the technology acquired, the presence or absence of separate cash flow, the development process and stage of completion, quantitative significance and our rationale for entering into the transaction.

If we acquire a business as defined under applicable accounting standards, then the acquired IPR&D is capitalized as an intangible asset. If we acquire an asset or group of assets that do not meet the definition of a business under applicable accounting standards, then the acquired IPR&D is expensed on its acquisition date. Future costs to develop these assets are recorded to research and development expense in our consolidated statements of income as they are incurred.

When performing our impairment assessment, we calculate the fair value using the same methodology as described above. If the carrying value of our acquired IPR&D exceeds its fair value, then the intangible asset is written down to its fair value. Changes in estimates and assumptions used in determining the fair value of our acquired IPR&D could result in an impairment. Impairments are recorded within amortization and impairment of acquired intangible assets in our consolidated statements of income.

Goodwill

Goodwill represents the difference between the purchase price and the fair value of the identifiable tangible and intangible net assets when accounted for using the purchase method of accounting. Goodwill is not amortized, but is reviewed for impairment annually, as of October 31, and whenever events or changes in circumstances indicate that the carrying value of the goodwill may not be recoverable.

We compare the fair value of our reporting unit to its carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of our reporting unit, we would record an impairment loss equal to the difference. As described in Note 25, Segment Information, to these consolidated financial statements, we operate as one operating segment, which is our only reporting unit.

Impairment of Long-Lived Assets

Long-lived assets to be held and used, including property, plant and equipment, and definite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets or asset group may not be recoverable.

Determination of recoverability is based on an estimate of undiscounted future cash flow resulting from the use of the asset and its eventual disposition. In the event that such cash flow is not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their fair values. Long-lived assets to be disposed of are carried at fair value less costs to sell.

Contingent Consideration

The consideration for our acquisitions often includes future payments that are contingent upon the occurrence of a particular event or events. We record an obligation for such contingent payments at fair value on the acquisition date. We estimate the fair value of contingent consideration obligations through valuation models that incorporate probability-adjusted assumptions related to the achievement of the milestones and thus likelihood of making related payments. We revalue our contingent consideration obligations each reporting period. Changes in the fair value of our contingent consideration obligations are recognized in our consolidated statements of income. Changes in the fair value of the contingent consideration obligations can result from changes to one or multiple inputs, including adjustments to the discount rates, changes in the amount or timing of expected expenditures associated with product development, changes in the amount or timing of cash flow and reserves associated with products upon commercialization, changes in the assumed achievement or timing of any cumulative sales-based and development milestones, changes in the probability of certain clinical events and changes in the assumed probability associated with regulatory approval.

Discount rates in our valuation models represent a measure of the credit risk associated with settling the liability. The period over which we discount our contingent obligations is based on the current development stage of the product candidates, our specific development plan for that product candidate adjusted for the probability of completing the development step and when the contingent payments would be triggered. In estimating the probability of success, we utilize data regarding similar milestone events from several sources, including industry studies and our own experience. These fair value measurements are based on significant inputs not observable in the market. Significant judgment is employed in determining the appropriateness of these assumptions as of the acquisition date and for each subsequent period.

Derivative Instruments and Hedging Activities

Cash Flow and Fair Value Derivative Instruments

We recognize all derivative instruments as either assets or liabilities at fair value in our consolidated balance sheets. Changes in the fair value of our derivative instruments are recognized each period in current earnings or AOCI, depending on whether the derivative instrument is designated as part of a hedge transaction and, if so, the type of hedge transaction. We classify the cash flow from these instruments in the same category as the cash flow from the hedged items. We do not hold or issue derivative instruments for trading or speculative purposes.

We assess at inception and on an ongoing basis, whether the derivative instruments that are used in hedging transactions are highly effective in offsetting the changes in cash flow or fair values of the hedged items. We exclude the forward points portion of the derivative instruments used in a hedging transaction from the effectiveness test and record the fair value gain or loss related to this portion each period in our consolidated statements of income in the same line as the underlying hedged item. If we determine that a forecasted transaction is no longer probable of occurring, we discontinue hedge accounting for the affected portion of the hedge instrument, and any related unrealized gain or loss on the contract is recognized in current earnings.

Net Investment Derivative Instruments

Designated net investment hedges are recognized as either assets or liabilities, at fair value, in our consolidated balance sheets. We hedge the changes in the spot exchange rate in AOCI and exclude changes to the forward rate and amortize the forward points in other (income) expense, net in our consolidated statements of income over the term of the contract. We classify the cash flow from these instruments in the same category as the cash flow from the hedged items.

Beginning in the second quarter of 2022 we no longer held net investment hedges as they were closed with the sale of our 49.9% equity interest in Samsung Bioepis in April 2022. For additional information on the sale of our equity interest in Samsung Bioepis, please read Note 3, Dispositions, to these consolidated financial statements.

For additional information on our derivative instruments and hedging activities, please read Note 10, Derivative Instruments, to these consolidated financial statements.

Translation of Foreign Currencies

The functional currency for most of our foreign subsidiaries is their local currency. For our non-U.S. subsidiaries that transact in a functional currency other than the U.S. dollar, assets and liabilities are translated at current rates of exchange at the balance sheet date. Income and expense items are translated at the average foreign currency exchange rates for the period. Adjustments resulting from the translation of the financial statements of our foreign operations into U.S. dollars are excluded from the determination of net income and are recorded in AOCI, as a separate component of equity. For subsidiaries where the functional currency of the assets and liabilities differ from the local currency, non-monetary assets and liabilities are translated at the rate of exchange in effect on the date assets were acquired while monetary assets and liabilities are translated at current rates of exchange as of the balance sheet date. Income and expense items are translated at the average foreign currency rates for the period. Translation adjustments of these subsidiaries are included in other (income) expense, net in our consolidated statements of income.

Royalty Cost of Sales

We make royalty payments to a number of third-parties under license or purchase agreements associated with our acquisition of intellectual property. These royalty payments are typically calculated as a percentage (royalty rate) of the sales of our products in a particular year. That royalty rate may remain constant, increase or decrease within each year based on the total amount of sales during the annual period. Each quarterly period, we estimate our total royalty obligation for the full year and recognize the proportional amount as cost of sales based on actual quarterly sales as a percentage of full year estimated sales. For example, if the level of net sales in any calendar year increases the royalty rate within the year, we will record our cost of sales at an even rate over the year, based on the estimated blended royalty rate.

Accounting for Share-Based Compensation

Our share-based compensation programs grant awards that have included stock options, restricted stock units that vest based on stock performance known as MSUs, time-vested RSUs, performance-vested stock units that settle in stock or cash (PSUs) and shares issued under our ESPP. Compensation expense is recognized based on the estimated fair value of the awards at grant date. We recognize compensation expense for the number of awards expected to vest after taking into consideration an estimate of award forfeitures over the requisite service period, which is generally the vesting period. Where awards are made with non-substantive vesting periods (for instance, where a portion of the award vests upon retirement eligibility), we estimate and recognize expense based on the period from the grant date to the date the employee becomes retirement eligible.

The fair values of our stock option grants are estimated as of the date of grant using a Black-Scholes option valuation model. The estimated fair values of the stock options are then expensed over the options' vesting periods.

The fair values of our MSUs and PSUs that settle in stock and have market-based metrics are estimated using a lattice model with a Monte Carlo simulation. We apply an accelerated attribution method to recognize share-based compensation expense over the applicable service period for these awards. The probability of actual shares expected to be earned is considered in the grant date valuation, therefore the expense is not adjusted to reflect the actual units earned.

The fair values of our RSUs are based on the market value of our stock on the date of grant. Compensation expense for RSUs is recognized straight-line over the applicable service period.

We apply an accelerated attribution method to recognize share-based compensation expense when accounting for our PSUs that settle in cash, and the fair value of the liability is remeasured at the end of each reporting period through expected settlement. Compensation expense associated with PSUs that settle in cash are based upon the stock price and the number of units expected to be earned after assessing the probability that certain performance criteria will be met and the targeted payout level associated with the performance criteria expected to be achieved. Cumulative adjustments are recorded each quarter to reflect changes in the stock price and estimated outcome of the performance-related conditions until the date results are determined and settled. If performance criteria are not met or not expected to be met, any compensation expense previously recognized to date associated with the awards will be reversed.

The fair values of PSUs that settle in stock and do not have market-based metrics are based upon the stock price on the date of grant. Compensation expense is recognized for the number of units expected to be earned after assessing the probability that certain performance criteria will be met and the targeted payout level associated with the performance criteria expected to be achieved. Cumulative adjustments are recorded each quarter to reflect the estimated outcome of the performance-related conditions until the date results are determined and settled. If performance criteria are not met or not expected to be met, any compensation expense previously recognized to date associated with the awards will be reversed.

Research and Development Expense

Research and development expense consists of expenses incurred in performing research and development activities, which include compensation and benefits, facilities and overhead expense, clinical trial expense and fees paid to CROs, clinical supply and manufacturing expense, write-offs of inventory that was previously capitalized in anticipation of product launch and determined to no longer be realizable and other outside expense and upfront fees and milestones paid to third-party collaborators. Research and development expense is expensed as incurred. Upfront and milestone payments made to third-party collaborators are expensed as incurred up to the point of regulatory approval. Milestone payments made upon regulatory approval are capitalized and amortized over the remaining useful life of the related product. Payments we make for research and development services prior to the services being rendered are recorded as prepaid assets in our consolidated balance sheets and are expensed as the services are provided. We also accrue the costs of ongoing clinical trials associated with programs that have been terminated or discontinued for which there is no future economic benefit at the time the decision is made to terminate or discontinue the program.

From time to time, we enter into development agreements in which we share expenses with a collaborative partner. We record payments received from our collaborative partners for their share of the development costs as a reduction of research and development expense, except as discussed in Note 19, Collaborative and Other Relationships, to these consolidated financial statements. Expenses incurred by Genentech in the ongoing development of RITUXAN,

GAZYVA, LUNSUMIO and other products for which an initial indication has been approved are not recorded as research and development expense, but rather reduce our share of profits recorded as a component of revenue from anti-CD20 therapeutic programs.

Selling, General and Administrative Expense

Selling, general and administrative expense is primarily comprised of compensation and benefits associated with sales and marketing, finance, human resources, legal, information technology and other administrative personnel, outside marketing, advertising and legal expense and other general and administrative costs.

Advertising costs are expensed as incurred. For the years ended December 31, 2023, 2022 and 2021, advertising costs totaled $71.4 million, $54.1 million and $98.7 million, respectively.

Income Taxes

The provision for income taxes includes federal, state, local and foreign taxes. Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be recovered or settled. We evaluate the realizability of our deferred tax assets and establish a valuation allowance when it is more likely than not that all or a portion of deferred tax assets will not be realized. We recognize deferred taxes associated with our GILTI tax calculations.

The income tax consequences from the intra-entity transfers of inventory within our consolidated group, both current and deferred, are recorded as a prepaid tax or deferred charge and recognized through our consolidated statements of income when the inventory is sold to a third-party. The income tax consequences from the intra-entity transfer of assets other than inventory and associated changes to deferred taxes are recognized when the transfer occurs.

We account for uncertain tax positions using a “more likely than not” threshold for recognizing and resolving uncertain tax positions. We evaluate uncertain tax positions on a quarterly basis and consider various factors including, but not limited to, changes in tax law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, information obtained during in process audit activities and changes in facts or circumstances related to a tax position. We also accrue for potential interest and penalties related to unrecognized tax benefits in income tax (benefit) expense in our consolidated statements of income.

Contingencies

We are currently involved in various claims and legal proceedings. Loss contingency provisions are recorded if the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount can be reasonably estimated or a range of loss can be determined. These accruals represent management’s best estimate of probable loss. Disclosure also is provided when it is reasonably possible that a loss will be incurred or when it is reasonably possible that the amount of a loss will exceed the recorded provision. On a quarterly basis, we review the status of each significant matter and assess its potential financial exposure. Significant judgment is required in both the determination of probability and as to whether an exposure is reasonably estimable. Because of uncertainties related to these matters, accruals are based only on the best information available at the time. As additional information becomes available, we reassess the potential liability related to pending claims and litigation and may change our estimates. Legal costs associated with legal proceedings are expensed when incurred.

Earnings per Share

Basic earnings per share is computed by dividing undistributed net income attributable to Biogen Inc. by the weighted-average number of common shares outstanding during the period. Diluted earnings per share is computed based on the treasury method by dividing net income by the weighted-average number of common shares outstanding during the period plus potentially dilutive common equivalent shares outstanding.

Business Combinations

Business combinations are recorded using the acquisition method of accounting. The results of operations of the acquired company are included in our results of operations beginning on the acquisition date, and assets acquired and liabilities assumed are recognized on the acquisition date at their respective fair values. Any excess of consideration transferred over the net carrying value of the assets acquired and liabilities assumed as of the acquisition date is recognized as goodwill.

We use the multi-period excess earnings method, which is a form of the income approach, utilizing post-tax cash flow and discount rates in estimating the fair value of identifiable intangible assets acquired when allocating the purchase consideration paid for the acquisition. The estimates of the fair value of identifiable intangible assets involve significant judgment by management and include assumptions with measurement uncertainty, such as the amount and timing of projected cash flow, long-term sales forecasts, discount rates and additionally for IPR&D intangible assets, the timing and probability of regulatory and commercial success.

We use the net realizable value method in estimating the fair value of acquired finished goods and work-in-process inventory. Raw materials acquired are valued using the replacement cost method.

Transaction and restructuring costs related to business combinations are expensed as incurred. The fair value of assets acquired and liabilities assumed in certain cases may be subject to revision based on the final determination of fair value during a period of time not to exceed 12 months from the acquisition date. If we determine the assets acquired do not meet the definition of a business, the transaction will be accounted for as an asset acquisition rather than a business combination.

New Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that we adopt as of the specified effective date. Unless otherwise discussed below, we do not believe that the adoption of recently issued standards have or may have a material impact on our consolidated financial statements or disclosures.

Segment Reporting

In November 2023 the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosure. This standard requires disclosure of significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit or loss, an amount and description of its composition for other segment items to reconcile to segment profit or loss and the title and position of the entity's CODM. The amendments in this update also expand the interim segment disclosure requirements. All disclosure requirements under this standard are also required for public entities with a single reportable segment. This standard is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted and the amendments in this update are required to be applied on a retrospective basis. We are currently evaluating the potential impact that this new standard will have on our consolidated financial statements and related disclosures.

Fair Value Measurements

In June 2022 the FASB issued ASU No. 2022-03, Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions. This standard clarifies that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. This standard became effective for us on January 1, 2024. We elected to early adopt this standard on a prospective basis during the third quarter of 2022. Upon adoption, we recorded an immaterial amount in other (income) expense, net in our consolidated statements of income.

Intangible Assets and Goodwill - Estimated Future Amortization of Intangible Assets (Details) $ in Millions	Dec. 31, 2023 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2024	$ 345.0
2025	470.0
2026	485.0
2027	480.0
2028	$ 495.0

Indebtedness

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Indebtedness


Note 13:			Indebtedness

Our indebtedness is summarized as follows:


	As of December 31,
(In millions)	2023		2022
Current portion:
2023 Term Loan 364-day tranche(1)	$	150.0	$	—
Current portion of notes payable and term loan	$	150.0	$	—
Non-current portion:
2023 Term Loan three-year tranche(1)	$	500.0	$	—
4.050% Senior Notes due September 15, 2025	1,746.6		1,744.7
2.250% Senior Notes due May 1, 2030	1,493.8		1,492.9
5.200% Senior Notes due September 15, 2045	1,100.7		1,100.3
3.150% Senior Notes due May 1, 2050	1,474.3		1,473.8
3.250% Senior Notes due February 15, 2051	472.8		469.3
Non-current portion of notes payable and term loan	$	6,788.2	$	6,281.0

As of December 31, 2023, we were in compliance with our senior note covenants and term loan covenants.

2023 Term Loan Credit Agreement

In connection with our acquisition of Reata in September 2023 we entered into a $1.5 billion term loan credit agreement (2023 Term Loan). On the closing date of the Reata acquisition we drew $1.0 billion from the 2023 Term Loan, comprised of a $500.0 million floating rate 364-day tranche and a $500.0 million floating rate three-year tranche. The remaining unused commitment of $500.0 million was terminated. During the fourth quarter of 2023 we repaid $350.0 million of the 364-day tranche. As of December 31, 2023, we had $650.0 million outstanding under the 2023 Term Loan, of which $150.0 million was outstanding under the 364-day tranche and $500.0 million was outstanding under the three-year tranche.

2021 Exchange Offer

In February 2021 we completed our private offer to exchange (Exchange Offer) our tendered 5.200% Senior Notes due September 15, 2045 (2045 Senior Notes) for a new series of 3.250% Senior Notes due February 15, 2051 (2051 Senior Notes) and cash, and an offer to purchase our tendered 2045 Senior Notes for cash.

An aggregate principal amount of approximately $624.6 million of our 2045 Senior Notes was exchanged for an aggregate principal amount of approximately $700.7 million of our 2051 Senior Notes and aggregate cash payments of approximately $151.8 million. Our Exchange Offer has been accounted for as a debt modification; as such, the cash component has been reflected as additional debt discount and is amortized as an adjustment to interest expense over the term of our 2051 Senior Notes.

In addition, we redeemed an aggregate principal amount of approximately $8.9 million of our 2045 Senior Notes for aggregate cash payments of approximately $12.1 million, excluding accrued and unpaid interest. The redemption has been accounted for as a debt extinguishment; as such, we recognized a pre-tax charge of $3.2 million upon the extinguishment of such 2045 Senior Notes. This charge, which was recognized in interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2021, reflects the payment of an early call premium and the write-off of the remaining unamortized original debt issuance costs and discount balances associated with such 2045 Senior Notes.

Upon settlement, we also made aggregate cash payments of approximately $13.8 million to settle all accrued and unpaid interest from the last interest payment date on our 2045 Senior Notes that were exchanged or redeemed. We incurred approximately $6.1 million of costs associated with our Exchange Offer, which was recognized in interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2021.

2020 Senior Notes

On April 30, 2020, we issued senior unsecured notes for an aggregate principal amount of $3.0 billion (2020 Senior Notes), consisting of the following:

•$1.5 billion aggregate principal amount of 2.25% Senior Notes due May 1, 2030, valued at 99.973% of par; and

•$1.5 billion aggregate principal amount of 3.15% Senior Notes due May 1, 2050, valued at 99.174% of par.

Our 2020 Senior Notes are senior unsecured obligations and may be redeemed at our option at any time at 100.0% of the principal amount plus accrued interest and, until a specified period before maturity, a specified make-whole amount. Our 2020 Senior Notes contain a change-of-control provision that, under certain circumstances, may require us to purchase our 2020 Senior Notes at a price equal to 101.0% of the principal amount plus accrued and unpaid interest to the date of repurchase.

The original costs associated with this offering of approximately $24.4 million have been recorded as a reduction to the carrying amount of the debt in our consolidated balance sheets. These costs along with the discounts will be amortized as additional interest expense using the effective interest rate method over the period from issuance through maturity. Interest on our 2020 Senior Notes is payable May 1 and November 1 of each year, commencing November 1, 2020.

2015 Senior Notes

The following is a summary of our currently outstanding senior unsecured notes issued in 2015 (the 2015 Senior Notes), consisting of the following:

•$1.75 billion aggregate principal amount of 4.05% Senior Notes due September 15, 2025, valued at 99.764% of par; and

•$1.12 billion aggregate principal amount of 5.20% Senior Notes due September 15, 2045, valued at 99.294% of par.

Our 2015 Senior Notes are senior unsecured obligations and may be redeemed at our option at any time at 100.0% of the principal amount plus accrued interest and a specified make-whole amount. Our 2015 Senior Notes contain a change of control provision that may require us to purchase the notes at a price equal to 101.0% of the principal amount plus accrued and unpaid interest to the date of purchase under certain circumstances.

The original costs associated with this offering of approximately $47.5 million have been recorded as a reduction to the carrying amount of the debt in our consolidated balance sheets. These costs along with the discounts will be amortized as additional interest expense using the effective interest rate method over the period from issuance through maturity.

3.625% Senior Notes due September 15, 2022

On September 15, 2015, we issued $1.0 billion aggregate principal amount of our 3.625% Senior Notes due September 15, 2022, at 99.920% of par. Our 3.625% Senior Notes were senior unsecured obligations. In July 2022 we redeemed our 3.625% Senior Notes prior to their maturity and recognized a net pre-tax charge of approximately $2.4 million upon the extinguishment of these Senior Notes, which primarily reflects the payment of an early call premium as well as the write-off of remaining unamortized original debt issuance costs and discount balances. These charges were recognized as interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2022.

2020 Revolving Credit Facility

In January 2020 we entered into a $1.0 billion, five-year senior unsecured revolving credit facility under which we are permitted to draw funds for working capital and general corporate purposes. The terms of the revolving credit facility

include a financial covenant that requires us not to exceed a maximum consolidated leverage ratio. As of December 31, 2023, we had no outstanding borrowings and were in compliance with all covenants under this facility.

Debt Maturity

The total gross payments due under our debt arrangements are as follows:


(In millions)	As of December 31, 2023
2024	$	150.0
2025	1,750.0
2026	500.0
2027	—
2028	—
2029 and thereafter	4,817.3
Total current and non-current debt	$	7,217.3
Less: debt discount and issuance fees	(279.1)
Total current and non-current debt, net	$	6,938.2

The fair value of our debt is disclosed in Note 8, Fair Value Measurements, to these consolidated financial statements.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2023

Investments, All Other Investments [Abstract]

Summary of financial assets with maturities of less than 90 days included within cash and cash equivalents

he following table summarizes our financial assets with maturities of less than 90 days from the date of purchase included in cash and cash equivalents in our consolidated balance sheets:


	As of December 31,
(In millions)	2023		2022
Commercial paper	$	—	$	177.2
Overnight reverse repurchase agreements	—		59.0
Money market funds	610.7		2,581.5
Short-term debt securities	—		29.9
Total	$	610.7	$	2,847.6

Marketable debt and equity securities

The following tables summarize our marketable debt and equity securities, classified as available for sale:


	As of December 31, 2023
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value












Marketable equity securities:
Marketable equity securities, current	$	31.6	$	—	$	(21.0)	$	10.6
Marketable equity securities, non-current	948.3		—		(542.1)		406.2
Total marketable equity securities	$	979.9	$	—	$	(563.1)	$	416.8


	As of December 31, 2022
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable debt securities:
Corporate debt securities:
Current	$	936.2	$	—	$	(4.9)	$	931.3
Non-current	305.3		0.1		(5.1)		300.3
Government securities:
Current	547.1		0.1		(5.0)		542.2
Non-current	271.4		—		(3.3)		268.1
Mortgage and other asset backed securities:
Current	—		—		—		—
Non-current	139.1		0.1		(1.9)		137.3
Total marketable debt securities	$	2,199.1	$	0.3	$	(20.2)	$	2,179.2

Marketable equity securities:

Marketable equity securities, non-current	$	1,133.8	$	—	$	(342.7)	$	791.1
Total marketable equity securities	$	1,133.8	$	—	$	(342.7)	$	791.1

Summary of contractual maturities: available-for-sale securities

The estimated fair value and amortized cost of our marketable debt securities classified as available-for-sale by contractual maturity are summarized as follows:



	As of December 31, 2022
(In millions)		Estimated Fair Value		Amortized Cost
Due in one year or less		$	1,473.5	$	1,483.3
Due after one year through five years		694.4		703.7
Due after five years		11.3		12.1
Total marketable debt securities		$	2,179.2	$	2,199.1

Proceeds from marketable securities, excluding strategic investments

The proceeds from maturities and sales of marketable debt securities and resulting realized gains and losses are summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Proceeds from maturities and sales	$	7,380.8	$	3,671.0	$	3,405.4
Realized gains	1.4		—		0.2
Realized losses	18.4		12.6		4.0

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Schedule of operating leases

All of our leases qualify as operating leases. The following table summarizes the presentation in our consolidated balance sheets of our operating leases:


		As of December 31,
(In millions)	Balance sheet location	2023		2022
Assets:
Operating lease assets	Operating lease assets	$	420.0	$	403.9

Liabilities
Current operating lease liabilities	Accrued expense and other	$	90.3	$	97.2
Non-current operating lease liabilities	Long-term operating lease liabilities	400.0		333.0
Total operating lease liabilities		$	490.3	$	430.2

Operating lease costs

The following table summarizes the effect of lease costs in our consolidated statements of income:


		For the Years Ended December 31,
(In millions)	Income Statement Location	2023		2022		2021
Operating lease cost	Research and development	$	2.0	$	2.0	$	3.4
	Selling, general and administrative	128.1		95.9		95.9
Variable lease cost	Research and development	0.5		0.4		0.8
	Selling, general and administrative	37.3		25.4		25.7
Sublease income	Selling, general and administrative	(23.5)		(24.0)		(23.9)
	Other (income) expense, net	(4.1)		(4.1)		(4.0)
Net lease cost		$	140.3	$	95.6	$	97.9

Operating lease liability maturity

The minimum lease payments for the next five years and thereafter are expected to be as follows:


(In millions)	As of December 31, 2023
2024	$	106.2
2025	96.1
2026	83.5
2027	86.1
2028	49.4
Thereafter	170.4
Total lease payments	$	591.7
Less: interest	101.4
Present value of operating lease liabilities	$	490.3

Operating lease weighted average remaining term and discount rate

The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows:


	As of December 31,
	2023		2022
Weighted average remaining lease term in years	7.37		4.64
Weighted average discount rate	4.5	%	3.7	%

Operating lease supplemental cash flow disclosure

Supplemental disclosure of cash flow information related to our operating leases included in cash flow provided by operating activities in our consolidated statements of cash flow is as follows:


	As of December 31,
(In millions)	2023		2022		2021
Cash paid for amounts included in the measurement of lease liabilities	$	116.4	$	107.4	$	105.8
Operating lease assets obtained in exchange for lease obligations	146.0		108.3		18.1

Inventory - Components of Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 27, 2023	Sep. 26, 2023	Dec. 31, 2022
Inventory [Line Items]
Raw materials	$ 426.9			$ 413.2
Work in process	1,926.8			751.9
Finished goods	255.4			200.4
Total inventory	2,609.1			1,365.5
Inventory, current	2,527.4			1,344.4
Inventory, noncurrent	81.7			$ 21.1
Reata Pharmaceuticals, Inc
Inventory [Line Items]
Inventory	$ 1,259.0	$ 1,300.0	$ 1,692.0

Property, Plant and Equipment - Narrative (Details) ft² in Thousands, $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2023 USD ($) ft²	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2023 USD ($)
Property, Plant and Equipment [Line Items]
Depreciation expense				$ 254.2	$ 272.4	$ 235.3
Interest costs capitalized				21.7	17.1	36.3
Construction in progress				975.4	888.8
Proceeds from divestiture of Hillerød, Denmark manufacturing operations				0.0	0.0	28.1
Gain on sale of building				0.0	503.7	$ 0.0
Property, plant and equipment, net				3,309.7	3,298.6
125 Broadway Building
Property, Plant and Equipment [Line Items]
Proceeds from divestiture of Hillerød, Denmark manufacturing operations	$ 603.0
Tenant allowance	10.8
Gain on sale of building	$ 503.7
Property, plant and equipment, net							$ 79.2
125 Broadway Building \| Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net							72.6
125 Broadway Building \| Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net							1.6
125 Broadway Building \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net							$ 5.0
Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Construction in progress				$ 728.8	$ 711.1
Property, plant and equipment, additions			$ 1,200.0
Solothurn, Switzerland \| Subsequent Event
Property, Plant and Equipment [Line Items]
Property, plant and equipment, additions		$ 710.7
Biologics Manufacturing \| Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²				393
Warehouse, Utilities and Support Space \| Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²				290
Administrative Space \| Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²				51

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flow from operating activities:
Net income	$ 1,161.5	$ 2,961.6	$ 1,727.6
Adjustments to reconcile net income to net cash flow from operating activities:
Depreciation and amortization	494.8	518.4	487.7
Impairment of intangible assets	0.0	119.6	629.3
Excess and obsolescence charges related to inventory	124.4	336.2	167.6
Amortization of inventory step-up	31.5	0.0	0.0
Acquired in-process research and development	0.0	0.0	18.0
Share-based compensation	264.2	254.1	238.6
Contingent consideration	0.0	(209.1)	(50.7)
Deferred income taxes	(305.8)	(168.6)	(426.8)
(Gain) loss on strategic investments	277.1	265.9	826.8
(Gain) loss on equity method investment	0.0	(2.6)	(34.9)
Gain on sale of equity interest in Samsung Bioepis	0.0	(1,505.4)	0.0
Gain on sale of building	0.0	(503.7)	0.0
Other	148.2	208.2	202.2
Changes in operating assets and liabilities, net of effects of business acquired:
Accounts receivable	61.3	(203.4)	324.8
Due from anti-CD20 therapeutic programs	(4.6)	(19.0)	1.2
Inventory	(130.9)	(320.2)	(462.4)
Accrued expense and other current liabilities	(201.6)	(113.4)	(95.4)
Income tax assets and liabilities	(299.0)	(142.3)	230.8
Other changes in operating assets and liabilities, net	(73.9)	(92.0)	(144.5)
Net cash flow provided by (used in) operating activities	1,547.2	1,384.3	3,639.9
Cash flow from investing activities:
Purchases of property, plant and equipment	(277.0)	(240.3)	(258.1)
Proceeds from sales and maturities of marketable securities	7,380.8	3,671.0	3,405.4
Purchases of marketable securities	(5,140.7)	(3,448.5)	(3,808.7)
Proceeds from sale of building	(6,926.1)
Proceeds from sale of equity interest in Samsung Bioepis	788.1	990.3	0.0
Proceeds from sale of building	0.0	582.6	0.0
Proceeds from divestiture of Hillerød, Denmark manufacturing operations	0.0	0.0	28.1
Acquired in-process research and development			(18.0)
Acquisitions of intangible assets	(34.4)	(2.9)	(18.8)
Proceeds from sales of strategic investments	119.6	0.0	93.5
Other	(11.3)	24.4	12.9
Net cash flow provided by (used in) investing activities	(4,101.0)	1,576.6	(563.7)
Cash flow from financing activities:
Purchase of treasury stock	0.0	(750.0)	(1,800.0)
Payments related to issuance of stock for share-based compensation arrangements, net	(44.3)	(1.9)	(0.7)
Repayments of borrowings and premiums paid	(809.9)	(1,002.2)	(170.0)
Proceeds from borrowings	997.2	0.0	0.0
Net (distribution) contribution to noncontrolling interest	12.3	12.4	(94.4)
Other	(6.0)	(5.6)	(21.1)
Net cash flow provided by (used in) financing activities	149.3	(1,747.3)	(2,086.2)
Net increase (decrease) in cash and cash equivalents	(2,404.5)	1,213.6	990.0
Effect of exchange rate changes on cash and cash equivalents	35.1	(55.7)	(59.8)
Cash and cash equivalents, beginning of the year	3,419.3	2,261.4	1,331.2
Cash and cash equivalents, end of the year	$ 1,049.9	$ 3,419.3	$ 2,261.4

Leases - Operating Lease Supplemental Cash Flow Disclosure (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 116.4	$ 107.4	$ 105.8
Operating lease assets obtained in exchange for lease obligations	$ 146.0	$ 108.3	$ 18.1

Guarantees

12 Months Ended

Dec. 31, 2023

Guarantees [Abstract]

Guarantees


Note 23:			Guarantees

As of December 31, 2023 and 2022, we did not have significant liabilities recorded for guarantees.

We enter into indemnification provisions under our agreements with other companies in the ordinary course of business, typically with business partners, contractors, clinical sites and customers. Under these provisions, we generally indemnify and hold harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of our activities. These indemnification provisions generally survive termination of the underlying agreement. The maximum potential amount of future payments we could be required to make under these indemnification provisions is unlimited. However, to date we have not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these agreements is minimal. Accordingly, we have no liabilities recorded for these agreements as of December 31, 2023 and 2022.

- Definition

The entire disclosure for each guarantee obligation, or each group of similar guarantee obligations, including (a) the nature of the guarantee, including its term, how it arose, and the events or circumstances that would require the guarantor to perform under the guarantee; (b) the maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee; (c) the current carrying amount of the liability, if any, for the guarantor's obligations under the guarantee; and (d) the nature of any recourse provisions under the guarantee, and any assets held either as collateral or by third parties, and any relevant related party disclosure. Excludes disclosures about product warranties.

+ References + Details

Collaborative and Other Relationships - OCREVUS (Details) - OCREVUS $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Collaborative arrangements and non-collaborative arrangement transactions
Royalty operating profit threshold for highest royalty rate percentage	$ 900.0
Reduction in royalty rate	50.00%
Collaboration agreement term	11 years
Foreign Tax Authority
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	3.00%
Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	13.50%
Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	24.00%

Share-Based Payments - Narrative (Details) $ / shares in Units, $ in Millions		1 Months Ended			3 Months Ended	12 Months Ended
	Sep. 26, 2023 USD ($)	Jun. 30, 2017 shares	Jun. 30, 2015 shares	May 31, 2006 shares	Mar. 31, 2019	Dec. 31, 2023 USD ($) plan increment $ / shares shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2014 increment
Share-based Compensation Arrangement by Share-based Payment Award
Selling, general and administrative						$ 2,549.7	$ 2,403.6	$ 2,674.3
Unrecognized compensation cost related to unvested share-based compensation						$ 287.4
Weighted-average period to recognize the cost of unvested awards (in years)						1 year 9 months 18 days
Number of share-based compensation plans pursuant to which awards are currently being made \| plan						3
Granted (in shares) \| shares						0
Shares issued under ESPP (in shares) \| shares			6,200,000
Reata Pharmaceuticals, Inc
Share-based Compensation Arrangement by Share-based Payment Award
Operating expenses	$ 393.4
Selling, general and administrative	196.4
Research and development expense asset acquired	$ 197.0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Share based payment arrangement, term						10 years
Market Stock Units (MSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Number of equal annual increments \| increment						3			4
Percentage of earnings of the target number of units granted based on actual stock performance						0.00%			0.00%
Percentage of earnings of the target number of units granted based on actual stock performance						200.00%			150.00%
Weighted average grant date fair value, nonvested \| $ / shares						$ 359.77	$ 366.52	$ 358.77
Total fair value of vested awards						$ 20.7	$ 18.8	$ 22.5
Granted (in dollars per share) \| $ / shares						$ 0		$ 358.77
Performance Units (PUs)
Share-based Compensation Arrangement by Share-based Payment Award
Number of days for calculation of average closing stock price						30 days
Total fair value of vested awards						$ 28.6	$ 9.5	$ 15.5
PSUs Settled in Stock
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period					3 years
Percentage of earnings of the target number of units granted based on actual stock performance						0.00%
Percentage of earnings of the target number of units granted based on actual stock performance						200.00%
Weighted average grant date fair value, nonvested \| $ / shares						$ 325.73	$ 292.95
Granted (in dollars per share) \| $ / shares						$ 383.61	$ 294.43	$ 276.61
PSUs Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period					3 years
Percentage of earnings of the target number of units granted based on actual stock performance						0.00%
Percentage of earnings of the target number of units granted based on actual stock performance						200.00%
Number of days for calculation of average closing stock price						30 days
Total fair value of vested awards						$ 11.7	$ 11.0	$ 9.9
Granted (in dollars per share) \| $ / shares						$ 383.61	$ 294.43
Time-Vested Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period						3 years
Weighted average grant date fair value, nonvested \| $ / shares						$ 256.74	$ 237.90
Total fair value of vested awards						$ 232.1	$ 116.3	$ 132.2
Granted (in dollars per share) \| $ / shares						$ 282.92	$ 221.28	$ 276.90
Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award
Total number of shares of common stock for issuance (in shares) \| shares				1,600,000
Ratio of total number of shares reserved under the plan				1.5
2017 Omnibus Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award
Ratio of total number of shares reserved under the plan		1.5
Omnibus Plan number of shares authorized (in shares) \| shares		8,000,000
2017 Omnibus Equity Plan \| Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award
Granted (in shares) \| shares						81,000
Stock options granted, weighted average price (in dollars per share) \| $ / shares						$ 139.10
Stock options granted, grant date fair value						$ 11.2
Vesting period						3 years

Dispositions (Details) ₩ in Millions, $ in Millions	1 Months Ended	12 Months Ended
Dispositions (Details) ₩ in Millions, $ in Millions	Apr. 30, 2022 USD ($)	Dec. 31, 2023 USD ($) payment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2022 KRW (₩)	Feb. 29, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of equity interest in Samsung Bioepis		$ (291.2)	$ (277.3)	$ (824.9)
Samsung Bioepis
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage					49.90%	15.00%	15.00%
Amount sold	$ 2,300.0
Investment in Samsung Bioepis						$ 45.0	₩ 49,500.0
Samsung Bioepis \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other current assets, receivable		$ 430.0	798.8
Samsung Bioepis \| Payment Due At First Anniversary \| Risk-adjusted discount rate \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Risk-adjusted discount rates		5.80%
Samsung Bioepis
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of interest in joint venture	1,000.0
Due from joint venture	1,300.0
Number of payments \| payment		2
Investment in Samsung Bioepis \| ₩					₩ 581.6
Gain on sale of equity interest in Samsung Bioepis		$ 1,500.0
Cumulative translation loss		58.9
Gain on derivative used in net investment hedge		57.0
Additional milestone payment	$ 50.0
Contingent discount on common shares	5.00%
Discrete income tax expense (benefit)		257.9
Samsung Bioepis \| Payment Due At First Anniversary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Due from joint venture	$ 812.5
Gain (loss) on sale		13.7	10.7
Samsung Bioepis \| Payment Due At Second Anniversary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Due from joint venture	$ 437.5
Gain (loss) on sale		$ 24.6	$ (1.4)

Indebtedness - Narrative (Details) - USD ($)		1 Months Ended			12 Months Ended
Indebtedness - Narrative (Details) - USD ($)	Sep. 26, 2023	Jul. 31, 2022	Feb. 28, 2021	Jan. 31, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Sep. 15, 2022	Apr. 30, 2020	Sep. 15, 2015
Debt Instrument
Interest rate on senior notes					3.625%
Aggregate principal amount, debt converted		$ 2,400,000
Senior notes aggregate principal amount										$ 1,000,000,000
Interest expense					$ 246,900,000	$ 246,600,000	$ 253,600,000
Redemption rate								99.92%
Revolving Credit Facility
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity				$ 1,000,000,000
Debt instrument, term				5 years
Outstanding borrowings					$ 0
2015 Senior Notes
Debt Instrument
Redemptions percentage of 2015 notes					100.00%
Redemption percentage for change in control provision					101.00%
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Debt Instrument
Aggregate principal amount, debt converted			$ 8,900,000
Aggregate cash payments			12,100,000
Loss on extinguishment of debt			3,200,000
Cash payments on debt extinguishment, including accrued interest			13,800,000
Interest expense			$ 6,100,000
Senior Notes \| 2020 Senior Notes
Debt Instrument
Senior notes aggregate principal amount									$ 3,000,000,000
Redemptions percentage of 2015 notes					100.00%
Redemption percentage for change in control provision					101.00%
Costs associated with the senior notes offerings					$ 24,400,000
Senior Notes \| 2.250% Senior Notes due May 1, 2030
Debt Instrument
Interest rate on senior notes					2.25%				2.25%
Senior notes aggregate principal amount									$ 1,500,000,000
Redemption percentage par value of senior notes									99.973%
Senior Notes \| 3.150% Senior Notes due May 1, 2050
Debt Instrument
Interest rate on senior notes					3.15%				3.15%
Senior notes aggregate principal amount									$ 1,500,000,000
Redemption percentage par value of senior notes									99.174%
Senior Notes \| 2015 Senior Notes
Debt Instrument
Costs associated with the senior notes offerings					$ 47,500,000
Senior Notes \| 4.050% Senior Notes due September 15, 2025
Debt Instrument
Interest rate on senior notes					4.05%
Senior notes aggregate principal amount					$ 1,750,000,000
Redemption percentage par value of senior notes					99.764%
Senior Notes \| 5.200% Senior Notes due September 15, 2045
Debt Instrument
Interest rate on senior notes			5.20%		5.20%
Aggregate principal amount, debt converted			$ 624,600,000
Senior notes aggregate principal amount					$ 1,120,000,000
Aggregate cash payments			$ 151,800,000
Redemption percentage par value of senior notes					99.294%
Senior Notes \| 3.250% Senior Notes due February 15, 2051
Debt Instrument
Interest rate on senior notes			3.25%		3.25%
Senior notes aggregate principal amount			$ 700,700,000
Line of Credit \| 2023 Term Loan
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity	$ 1,500,000,000				$ 650,000,000
Unused borrowing capacity, amount	500,000,000
Line of Credit \| 2023 Term Loan \| Reata Pharmaceuticals, Inc
Debt Instrument
Proceeds from long-term lines of credit	1,000,000,000
Line of Credit \| 2023 Term Loan \| Floating Rate 364-Day Tranche
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity					150,000,000
Repayments of short-term debt, maturing in more than three months	350,000,000
Line of Credit \| 2023 Term Loan \| 2023 Term loan three-year tranche
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity					$ 500,000,000
Line of Credit \| 2023 Term Loan \| 2023 Term loan three-year tranche \| Reata Pharmaceuticals, Inc
Debt Instrument
Proceeds from long-term lines of credit	$ 500,000,000

Acquisitions -Narrative (Details) $ / shares in Units, $ in Millions		3 Months Ended		12 Months Ended
	Sep. 26, 2023 USD ($) ft² $ / shares	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 27, 2023 USD ($)
Business Acquisition [Line Items]
Selling, general and administrative				$ 2,549.7	$ 2,403.6	$ 2,674.3
Long-term debt, gross		$ 7,217.3	$ 7,217.3	7,217.3
Goodwill		6,219.2	6,219.2	6,219.2	$ 5,749.0	$ 5,761.1
Reata Pharmaceuticals, Inc
Business Acquisition [Line Items]
Price per share \| $ / shares	$ 172.50
Total transaction value	$ 6,602.9
Outstanding equity awards				983.9
Consideration transferred, equity compensation pre-acquisition services	590.5
Operating expenses	393.4
Selling, general and administrative	196.4
Research and development expense asset acquired	197.0
Inventory	$ 1,692.0	1,259.0	1,259.0	1,259.0			$ 1,300.0
Inventory amortization period	3 years
Measurement Period Adjustments, Inventory		31.5	(433.0)
Fair value indefinite lived intangible assets discount rate	14.30%
Operating lease area \| ft²	327,400
Operating lease, contract term	16 years
Operating lease liabilities	$ 151.8	151.8	151.8	151.8			151.8
Remaining lease term	15 years
Operating lease assets	$ 122.4	121.2	121.2	121.2			121.2
Goodwill	1,057.3	464.5	464.5	464.5			464.5
Reata Pharmaceuticals, Inc \| Secured Debt \| The Credit Facility \| Line of Credit
Business Acquisition [Line Items]
Long-term debt, gross	1,000.0
Reata Pharmaceuticals, Inc \| Selling, general and administrative
Business Acquisition [Line Items]
Separately recognized transactions, additional disclosures, acquisition cost expensed				28.4
Reata Pharmaceuticals, Inc \| Completed technology for SKYCLARYS (U.S.)
Business Acquisition [Line Items]
Intangible assets:	3,600.0	4,200.0	4,200.0	4,200.0			4,200.0
Reata Pharmaceuticals, Inc \| In-process research and development
Business Acquisition [Line Items]
Intangible assets:	1,900.0	2,300.0	2,300.0	2,300.0			2,300.0
Reata Pharmaceuticals, Inc \| Priority review voucher
Business Acquisition [Line Items]
Intangible assets:	100.0	100.0	100.0	100.0
Reata Pharmaceuticals, Inc \| Other clinical programs
Business Acquisition [Line Items]
Intangible assets:	$ 20.0	$ 40.0	$ 40.0	$ 40.0			$ 40.0

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases


Note 12:			Leases

We lease real estate, including laboratory and office space, and certain equipment.

Our leases have remaining lease terms ranging from less than one year to fifteen years. Certain leases include one or more options to renew, exercised at our sole discretion, with renewal terms that can extend the lease term from one year to ten years.

In addition, we sublease certain real estate to third parties. Our sublease portfolio consists of operating leases, with remaining lease terms ranging from one year to six years.

All of our leases qualify as operating leases. The following table summarizes the presentation in our consolidated balance sheets of our operating leases:


		As of December 31,
(In millions)	Balance sheet location	2023		2022
Assets:
Operating lease assets	Operating lease assets	$	420.0	$	403.9

Liabilities
Current operating lease liabilities	Accrued expense and other	$	90.3	$	97.2
Non-current operating lease liabilities	Long-term operating lease liabilities	400.0		333.0
Total operating lease liabilities		$	490.3	$	430.2

The following table summarizes the effect of lease costs in our consolidated statements of income:


		For the Years Ended December 31,
(In millions)	Income Statement Location	2023		2022		2021
Operating lease cost	Research and development	$	2.0	$	2.0	$	3.4
	Selling, general and administrative	128.1		95.9		95.9
Variable lease cost	Research and development	0.5		0.4		0.8
	Selling, general and administrative	37.3		25.4		25.7
Sublease income	Selling, general and administrative	(23.5)		(24.0)		(23.9)
	Other (income) expense, net	(4.1)		(4.1)		(4.0)
Net lease cost		$	140.3	$	95.6	$	97.9

Variable lease cost primarily related to operating expense, taxes and insurance associated with our operating leases. As these costs are generally variable in nature, they are not included in the measurement of the operating lease asset and related lease liability.

The minimum lease payments for the next five years and thereafter are expected to be as follows:


(In millions)	As of December 31, 2023
2024	$	106.2
2025	96.1
2026	83.5
2027	86.1
2028	49.4
Thereafter	170.4
Total lease payments	$	591.7
Less: interest	101.4
Present value of operating lease liabilities	$	490.3

The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows:


	As of December 31,
	2023		2022
Weighted average remaining lease term in years	7.37		4.64
Weighted average discount rate	4.5	%	3.7	%

Supplemental disclosure of cash flow information related to our operating leases included in cash flow provided by operating activities in our consolidated statements of cash flow is as follows:


	As of December 31,
(In millions)	2023		2022		2021
Cash paid for amounts included in the measurement of lease liabilities	$	116.4	$	107.4	$	105.8
Operating lease assets obtained in exchange for lease obligations	146.0		108.3		18.1

6100 Legacy Drive Lease

In connection with our acquisition of Reata we assumed responsibility for a single-tenant, build-to-suit building of approximately 327,400 square feet of office and laboratory space located in Plano, Texas, with an initial lease term of 16 years. We recorded a lease liability of approximately $151.8 million, which represents the net present value of rental expense over the remaining lease term of approximately 15 years, with a corresponding right-of-use asset of approximately $121.2 million, which represents our estimate of the fair value for a market participant of the current rental market in the Dallas, Texas area. Included in our estimate of the market rental rate is the value of any leasehold improvements or tenant allowances related to the building. We do not intend to occupy this building and are evaluating opportunities to sublease the property.

For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these consolidated financial statements.

125 Broadway Building Sale and Leaseback Transaction

In connection with the sale of our 125 Broadway building during the third quarter of 2022, we simultaneously leased back the building for a term of approximately 5.5 years, which resulted in the recognition of approximately $168.2 million in a new lease liability and right-of-use asset recorded within our consolidated balance sheets as of December 31, 2022. The sale and immediate leaseback of this building qualified for sale and leaseback treatment and is classified as an operating lease. For additional information on the sale of our 125 Broadway building, please read Note 11, Property, Plant and Equipment, to these consolidated financial statements.

300 Binney Street Lease Modification

In September 2022 we entered into an agreement to partially terminate a portion of our lease located at 300 Binney Street, as well as to reduce the lease term for the majority of the remaining space. The agreement was driven by our 2022 efforts to reduce costs by consolidating real estate locations. The transaction was treated as a lease modification as of the effective date and resulted in the derecognition of a right-of-use asset of approximately $47.4 million and a lease liability of approximately $52.7 million, which resulted in a gain of approximately $5.3 million, which was recorded within restructuring charges in our consolidated statements of income for the year ended December 31, 2022.

Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment Estimated Useful Lives (Details)	Dec. 31, 2023
Minimum \| Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Minimum \| Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Minimum \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Minimum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Maximum \| Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years
Maximum \| Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	7 years
Maximum \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	20 years
Maximum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years

Acquisitions (Tables)

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Schedule of Business Acquisitions, by Acquisition

Total consideration transferred for the acquisition of Reata is summarized as follows:


(In millions)	As of September 26, 2023
Cash consideration paid to Reata shareholders(1)	$	6,602.9
Fair value of Reata equity compensation pre-acquisition services and related taxes(2)	590.5
Total consideration	$	7,193.4

(1) Represents cash consideration transferred of $172.50 per outstanding Reata ordinary share based on 38.3 million Reata shares outstanding at closing.

(2) Represents the fair value of Reata stock options and stock units issued to Reata equity award holders and the related taxes attributable to pre-acquisition vesting services.

The related impact to our consolidated statements of income that would have been recognized in previous periods if the adjustments were recognized as of the acquisition date is immaterial.


(In millions)	Amounts Recognized as of Acquisition Date (as previously reported)		Measurement Period Adjustments		Amounts Recognized as of Acquisition Date (as adjusted)
Cash and cash equivalents	$	267.3	$	—	$	267.3
Accounts receivable	15.9		—		15.9
Inventory	1,692.0		(433.0)		1,259.0
Other current assets	53.6		—		53.6
Intangible assets:
Completed technology for SKYCLARYS (U.S.)	3,600.0		600.0		4,200.0
In-process research and development (omaveloxolone)	1,900.0		400.0		2,300.0
Priority review voucher	100.0		—		100.0
Other clinical programs	20.0		20.0		40.0
Operating lease assets	122.4		(1.2)		121.2
Accrued expense and other	(98.9)		(2.6)		(101.5)
Debt payable	(159.9)		—		(159.9)
Contingent payable to Blackstone(1)	(300.0)		—		(300.0)
Deferred tax liability	(922.5)		10.1		(912.4)
Operating lease liabilities	(151.8)		—		(151.8)
Other assets and liabilities, net	(2.0)		(0.5)		(2.5)
Total identifiable net assets	6,136.1		592.8		6,728.9
Goodwill	1,057.3		(592.8)		464.5
Total assets acquired and liabilities assumed	$	7,193.4	$	—	$	7,193.4

(1) For additional information on the contingent payable to Blackstone, please read Note 18, Other Consolidated Financial Statement Detail, to these consolidated financial statements.

Restructuring - Narrative (Details) $ in Millions		12 Months Ended
Restructuring - Narrative (Details) $ in Millions	Sep. 26, 2023 USD ($)	Dec. 31, 2023 USD ($) employee
Minimum
Restructuring Cost and Reserve [Line Items]
Expected cost remaining		$ 260.0
Maximum
Restructuring Cost and Reserve [Line Items]
Expected cost remaining		$ 280.0
2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Expected operating expense reduction	$ 1,000.0
Expected number of positions eliminated \| employee		1,000
Severance Costs		$ 153.4
Restructuring charges \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs		153.4
Reata Pharmaceuticals, Inc
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 30.4

Revenue - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
Revenue - Narrative (Details) $ in Millions	Jun. 30, 2020 USD ($) payment	Dec. 31, 2023 wholesaler	Dec. 31, 2022	Dec. 31, 2021	Jul. 31, 2023
Disaggregation of Revenue [Line Items]
Number of wholesalers \| wholesaler		2
Percentage of total revenues		17.20%	16.70%	15.10%
Contract manufacturing revenue
Disaggregation of Revenue [Line Items]
Remaining performance obligation, amount \| $	$ 500.0
Revenue, Remaining Performance Obligation, Number Of Payments \| payment	3
LEQEMBI Collaboration
Disaggregation of Revenue [Line Items]
Share of non-controling interest recognized		50.00%			50.00%
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors		27.00%	26.80%	28.80%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors		9.90%	11.10%	10.10%
Distributor One
Disaggregation of Revenue [Line Items]
Percentage receivables of wholesale distributor accounted in consolidated receivables		24.60%	22.70%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage receivables of wholesale distributor accounted in consolidated receivables		11.60%	10.90%

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Business Overview

For additional information on our collaboration arrangements, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in this report.

Consolidation

Use of Estimates

Revenue Recognition

Product Revenue

Reserves for Discounts and Allowances

Product revenue reserves, which are classified as a reduction in product revenue, are generally characterized in the following categories: discounts, contractual adjustments and returns.

Revenue from Anti-CD20 Therapeutic Programs

Revenue from anti-CD20 therapeutic programs consist of:

(i) our share of pre-tax profits and losses in the U.S. for RITUXAN, GAZYVA and LUNSUMIO;

(ii) royalty revenue on sales of OCREVUS; and

For additional information on our relationship with Genentech, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Contract Manufacturing, Royalty and Other Revenue

Contract Manufacturing Revenue

Royalty and Other Revenue

Collaborative and Other Relationships

Fair Value Measurements

•Level 1 — Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access;

•Level 3 — Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

Other Assets and Liabilities

Cash and Cash Equivalents

Accounts Receivable

We do not adjust our receivables for the effects of a significant financing component at contract inception if we expect to collect the receivables in one year or less from the time of sale.

Receivables from Samsung BioLogics

Concentration of Credit Risk

Marketable Securities and Other Investments

Marketable Debt Securities

Marketable Equity Securities and Venture Capital Funds

Non-Marketable Equity Securities

Evaluating Marketable Debt Securities for Other-than-Temporary Impairments

Equity Method of Accounting

Inventory

Capitalization of Inventory Costs

Obsolescence and Unmarketable Inventory

Property, Plant and Equipment


Asset Category			Useful Lives
Land			Not depreciated
Buildings			15 to 40 years
Leasehold Improvements			Lesser of the useful life or the term of the respective lease
Furniture and Fixtures			5 to 7 years
Machinery and Equipment			5 to 20 years
Computer Software and Hardware			3 to 5 years

Leases

Intangible Assets

Acquired In-process Research and Development

Goodwill

Impairment of Long-Lived Assets

Contingent Consideration

Derivative Instruments and Hedging Activities

Cash Flow and Fair Value Derivative Instruments

Net Investment Derivative Instruments

For additional information on our derivative instruments and hedging activities, please read Note 10, Derivative Instruments, to these consolidated financial statements.

Translation of Foreign Currencies

Royalty Cost of Sales

Accounting for Share-Based Compensation

The fair values of our RSUs are based on the market value of our stock on the date of grant. Compensation expense for RSUs is recognized straight-line over the applicable service period.

Research and Development Expense

Selling, General and Administrative Expense

Advertising costs are expensed as incurred.

Income Taxes

Contingencies

Earnings per Share

Business Combinations

We use the net realizable value method in estimating the fair value of acquired finished goods and work-in-process inventory. Raw materials acquired are valued using the replacement cost method.

New Accounting Pronouncements

Segment Reporting

Fair Value Measurements

Leases - Operating Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net lease cost	$ 140.3	$ 95.6	$ 97.9
Research and development
Operating lease cost	2.0	2.0	3.4
Variable lease cost	0.5	0.4	0.8
Selling, general and administrative
Operating lease cost	128.1	95.9	95.9
Variable lease cost	37.3	25.4	25.7
Sublease income	(23.5)	(24.0)	(23.9)
Other (income) expense, net
Sublease income	$ (4.1)	$ (4.1)	$ (4.0)

Revenue - Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 9,835.6	$ 10,173.4	$ 10,981.7
Royalty revenue on sales of OCREVUS
Disaggregation of Revenue [Line Items]
Revenue	1,266.2	1,136.3	991.7
Revenue from anti-CD20 therapeutic programs
Disaggregation of Revenue [Line Items]
Revenue	1,689.6	1,700.5	1,658.5
Genentech
Disaggregation of Revenue [Line Items]
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4	547.0	647.7
Royalty revenue on sales of OCREVUS	$ 14.0	$ 17.2	$ 19.1

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

- Definition

+ References

+ Details

Intangible Assets and Goodwill - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Sep. 27, 2023	Sep. 26, 2023
Goodwill [Line Items]
Amortization and impairment of acquired intangible assets			$ 240,600,000	$ 365,900,000	$ 881,300,000
Amortization of acquired intangible assets			240,600,000	246,300,000	252,000,000
(Gain) loss on fair value remeasurement of contingent consideration			0	$ (209,100,000)	(50,700,000)
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]				Amortization and impairment of acquired intangible assets
Accumulated impairment losses related to goodwill			$ 0
Acquired and in-licensed rights and patents
Goodwill [Line Items]
Weighted-Average remaining useful life			12 years
Acquired and in-licensed rights and patents \| Minimum
Goodwill [Line Items]
Estimated life (in years)			2 years
Acquired and in-licensed rights and patents \| Maximum
Goodwill [Line Items]
Estimated life (in years)			22 years
Developed technology and other
Goodwill [Line Items]
Weighted-Average remaining useful life			10 years
Developed technology and other \| Minimum
Goodwill [Line Items]
Estimated life (in years)			13 years
Developed technology and other \| Maximum
Goodwill [Line Items]
Estimated life (in years)			31 years
Completed Technology \| Minimum
Goodwill [Line Items]
Estimated life (in years)			2 years
Completed Technology \| Maximum
Goodwill [Line Items]
Estimated life (in years)			31 years
TGN
Goodwill [Line Items]
(Gain) loss on fair value remeasurement of contingent consideration			$ 209,100,000
TGN \| In-process research and development
Goodwill [Line Items]
Impairment of intangible assets		$ 44,300,000		$ 119,600,000
BIIB111
Goodwill [Line Items]
Impairment of intangible assets				365,000,000
BIIB111 \| In-process research and development
Goodwill [Line Items]
Intangible asset, fair value	$ 0		0
BIIB112
Goodwill [Line Items]
Impairment of intangible assets					220,000,000
BIIB112 \| In-process research and development
Goodwill [Line Items]
Intangible asset, fair value	0		0
BIIB111 and BIIB112
Goodwill [Line Items]
Manufacturing and other costs	$ 39,100,000
Convergence Pharmaceuticals \| TGN \| In-process research and development
Goodwill [Line Items]
Finite-Lived Intangible Assets Acquired			424,600,000
Nightstar \| BIIB111
Goodwill [Line Items]
Impairment of intangible assets					$ 365,000,000
Nightstar \| BIIB111 \| In-process research and development
Goodwill [Line Items]
Finite-Lived Intangible Assets Acquired			480,000,000
Nightstar \| BIIB112
Goodwill [Line Items]
Impairment of intangible assets				$ 220,000,000
Nightstar \| BIIB112 \| In-process research and development
Goodwill [Line Items]
Finite-Lived Intangible Assets Acquired			220,000,000
Reata Pharmaceuticals, Inc \| In-process research and development
Goodwill [Line Items]
Intangible assets:			2,300,000,000			$ 2,300,000,000	$ 1,900,000,000
Reata Pharmaceuticals, Inc \| Completed technology for SKYCLARYS (U.S.)
Goodwill [Line Items]
Intangible assets:			4,200,000,000			$ 4,200,000,000	3,600,000,000
Reata Pharmaceuticals, Inc \| Priority review voucher
Goodwill [Line Items]
Intangible assets:			$ 100,000,000.0				$ 100,000,000.0

Collaborative and Other Relationships - Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Revenue	$ 9,835.6	$ 10,173.4	$ 10,981.7
Royalty revenue on sales of OCREVUS
Collaborative arrangements and non-collaborative arrangement transactions
Revenue	1,266.2	1,136.3	991.7
Revenue from anti-CD20 therapeutic programs
Collaborative arrangements and non-collaborative arrangement transactions
Revenue	1,689.6	1,700.5	1,658.5
Genentech
Collaborative arrangements and non-collaborative arrangement transactions
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	409.4	547.0	647.7
Royalty revenue on sales of OCREVUS	$ 14.0	$ 17.2	$ 19.1

- Definition

+ References

+ Details

Other Consolidated Financial Statement Detail - Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Mar. 31, 2022	Feb. 29, 2012
Collaborative arrangements and non-collaborative arrangement transactions
Gain on sale of equity interest in Samsung Bioepis		$ 0.0	$ (1,505.4)	$ 0.0
Litigation settlement agreement and settlement fees	$ 900.0	0.0	917.0	0.0
Interest income		(276.5)	(89.3)	(11.0)
Interest expense		246.9	246.6	253.6
(Gains) losses on investments, net		291.2	277.3	824.9
Foreign exchange (gains) losses, net		50.4	35.5	22.4
Other, net		3.5	10.1	5.6
Other (income) expense		$ 315.5	$ (108.2)	$ 1,095.5
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Ownership percentage					49.90%	15.00%

Earnings per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income attributable to Biogen Inc.	$ 1,161.1	$ 3,046.9	$ 1,556.1
Denominator:
Weighted average number of common shares outstanding (in shares)	144,700	145,300	149,100
Effect of dilutive securities:
Dilutive potential common shares (in shares)	900	700	500
Shares used in calculating diluted earnings per share (in shares)	145,600	146,000	149,600
Time-vested restricted stock units
Effect of dilutive securities:
Dilutive securities (in shares)	700	500	300
Market stock units
Effect of dilutive securities:
Dilutive securities (in shares)	0	100	100
Performance stock units settled in stock
Effect of dilutive securities:
Dilutive securities (in shares)	200	100	100

Other Consolidated Financial Statement Detail (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Supplemental cash flow information

Supplemental disclosure of cash flow information for the years ended December 31, 2023, 2022 and 2021, is as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Cash paid during the year for:
Interest	$	252.2	$	262.5	$	280.8
Income taxes	740.7		932.9		247.9

Other income (expense), net

Components of other (income) expense, net, are summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Gain on sale of equity interest in Samsung Bioepis(1)	$	—	$	(1,505.4)	$	—
Litigation settlement agreement and settlement fees	—		917.0		—
Interest income	(276.5)		(89.3)		(11.0)
Interest expense	246.9		246.6		253.6
(Gains) losses on investments, net	291.2		277.3		824.9
Foreign exchange (gains) losses, net	50.4		35.5		22.4
Other, net	3.5		10.1		5.6
Total other (income) expense, net	$	315.5	$	(108.2)	$	1,095.5

Gain (loss) on investments

The following table summarizes our (gains) losses on investments, net that relates to our equity securities held as of December 31, 2023, 2022 and 2021:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Net (gains) losses recognized on equity securities	$	275.2	$	264.7	$	821.1
Less: Net (gains) losses realized on equity securities	5.2		—		(10.3)
Net unrealized (gains) losses recognized on equity securities	$	270.0	$	264.7	$	831.4

Accrued expense and other

Accrued expense and other consists of the following:


	As of December 31,
(In millions)	2023		2022

Revenue-related reserves for discounts and allowances	$	926.5	$	891.6
Employee compensation and benefits	335.1		395.6
Collaboration expense	214.6		277.9
Royalties and licensing fees	191.5		209.4



Reata acquisition-related accrued expense	117.5		—
Other	838.4		746.9
Total accrued expense and other	$	2,623.6	$	2,521.4

Pay vs Performance Disclosure - USD ($) $ in Millions	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net income attributable to Biogen Inc.	$ 1,161.1	$ 3,046.9	$ 1,556.1

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
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+ Details

Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2023

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Foreign currency forward contracts that were entered into to hedge forecasted revenue

The notional amount of foreign currency forward contracts and foreign currency options that were entered into to hedge forecasted revenue and operating expense is summarized as follows:


	Notional Amount As of December 31,
(In millions)	2023		2022
Euro	$	1,169.0	$	1,495.5
British pound	—		162.8
Swiss franc	—		—
Canadian dollar	—		57.2
Total foreign currency forward contracts and options	$	1,169.0	$	1,715.5

Summary of unrealized gain (loss) on derivative instruments that are included in AOCI

The pre-tax portion of the fair value of these foreign currency forward contracts and foreign currency options that were included in AOCI in total equity is summarized as follows:


	For the Years Ended December 31,
(In millions)	2023		2022		2021
Unrealized gains	$	—	$	29.9	$	60.8
Unrealized (losses)	(34.8)		(21.3)		(7.0)
Net unrealized gains (losses)	$	(34.8)	$	8.6	$	53.8

Summary of the effect of derivatives designated as cash flow hedging instruments on our consolidated statements of income

The following table summarizes the effect of foreign currency forward contracts and forward currency options designated as hedging instruments in our consolidated statements of income:


For the Years Ended December 31,
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)							Net Gains/(Losses) Recognized in Operating Income (in millions)
Location	2023		2022		2021		Location	2023		2022		2021
Revenue	$	11.6	$	201.6	$	(60.0)	Revenue	$	(2.4)	$	(8.6)	$	(8.4)
Operating expense	3.7		(5.5)		(0.8)		Operating expense	—		—		—

Summary of the effect of derivatives designated as net investment hedging instruments on our consolidated statement of income

The following table summarizes the effect of our net investment hedges in our consolidated financial statements:


For the Years Ended December 31,
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion) (in millions)			Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions)			Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)
Location	2022		2021		Location	2022		2021		Location	2022		2021
Gains (losses) on net investment hedge(1)	$	20.4	$	46.0	Gains (losses) on net investment hedge(1)	$	(3.2)	$	(3.2)	Other (income) expense(1)	$	(4.6)	$	(0.6)

Summary of the fair value for our outstanding derivatives

The following table summarizes the fair value and presentation in our consolidated balance sheets of our outstanding derivative instruments, including those designated as hedging instruments:


		As of December 31,
(In millions)	Balance Sheet Location	2023		2022
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	0.3	$	37.9

Liability derivative instruments	Accrued expense and other	26.5		18.4


Other Derivative Instruments:
Asset derivative instruments	Other current assets	11.6		25.1
Liability derivative instruments	Accrued expense and other	5.1		7.6