0000875045-23-000038 | 10-Q | XBRL Viewer

Restructuring, Business Transformation and Other Cost Saving Initiatives

9 Months Ended

Sep. 30, 2023

Restructuring and Related Activities [Abstract]

Restructuring, Business Transformation and Other Cost Saving Initiatives

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 reduction of approximately 1,000 employees.

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


	For the Three Months Ended September 30, 2023				For the Nine Months Ended September 30, 2023

(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs		Total
Selling, general and administrative	$	—	$	5.9	$	5.9	$	—	$	17.4	$	17.4
Research and development	—		0.2		0.2		—		0.7		0.7
Restructuring charges	37.7		17.3		55.0		62.6		33.8		96.4
Total charges	$	37.7	$	23.4	$	61.1	$	62.6	$	51.9	$	114.5

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 closing of the Reata acquisition, we implemented an integration plan designed to realize operating synergies through cost savings and avoidance. We expect to incur restructuring charges of approximately $30.0 million in 2023. These amounts are primarily related to severance and are expected to be paid by the end of 2024. For the three and nine months ended September 30, 2023, we recognized approximately $21.0 million of net pre-tax restructuring charges, primarily consisting of 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 Three Months Ended September 30,
	2023						2022
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs(1)		Total
Restructuring charges	$	—	$	—	$	—	$	21.6	$	(6.2)	$	15.4
Total charges	$	—	$	—	$	—	$	21.6	$	(6.2)	$	15.4

	For the Nine Months Ended September 30,
	2023						2022
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs(1)		Total
Restructuring charges	$	—	$	2.6	$	2.6	$	110.2	$	13.9	$	124.1
Total charges	$	—	$	2.6	$	2.6	$	110.2	$	13.9	$	124.1

(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.

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


	Workforce Reductions
(In millions)	2023		2022

Restructuring reserve as of December 31	$	35.9		$	—
Expense	7.1			27.7
Payment	(15.6)			(6.2)
Foreign currency and other adjustments	0.6			—
Restructuring reserve as of March 31	28.0			21.5
Expense	17.8			60.9
Payment	(13.4)			(29.7)
Foreign currency and other adjustments	(0.1)			(0.5)
Restructuring reserve as of June 30	32.3			52.2
Expense	58.7			21.6
Payment	(31.8)			(32.3)
Foreign currency and other adjustments	0.1			(1.3)
Restructuring reserve as of September 30	$	59.3		$	40.2

Goodwill and Intangible Assets Disclosure [Text Block]

Intangible Assets

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


		As of September 30, 2023						As of December 31, 2022
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology	4-28 years	$	11,053.8	$	(5,793.2)	$	5,260.6	$	7,415.3	$	(5,629.2)	$	1,786.1
In-process research and development	Indefinite until commercialization	1,920.0		—		1,920.0		—		—		—
Priority review voucher	Indefinite	100.0		—		100.0		—		—		—
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	13,137.8	$	(5,793.2)	$	7,344.6	$	7,479.3	$	(5,629.2)	$	1,850.1

Amortization and Impairments

For the three and nine months ended September 30, 2023, amortization and impairment of acquired intangible assets totaled $60.9 million and $164.0 million, respectively, compared to $56.5 million and $190.9 million, respectively, in the prior year comparative periods. For the three and nine months ended September 30, 2023 and 2022, we had no impairment charges.

Completed Technology

Completed technology primarily relates to our other marketed products and programs acquired through asset acquisitions, licenses and business combinations. 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

$3.6 billion.

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. Upon commercialization, we will determine the estimated useful life and amortize these amounts based upon an economic consumption method. IPR&D balances also include adjustments related to foreign currency exchange rate fluctuations. The carrying value associated with our IPR&D assets as of September 30, 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 $1.9 billion.

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 condensed consolidated financial statements.

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 September 30, 2023
2023 (remaining three months)	$	75.0
2024	325.0
2025	430.0
2026	440.0
2027	435.0
2028	445.0

Goodwill

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


(In millions)	As of September 30, 2023
Goodwill, December 31, 2022	$	5,749.0
Goodwill resulting from Reata acquisition	1,057.3
Other	1.2
Goodwill, September 30, 2023	$	6,807.5

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

As of September 30, 2023, we had no accumulated impairment losses related to goodwill. Other includes adjustments related to foreign currency exchange rate fluctuations.

Inventory - Components of Inventory (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Raw materials	$ 437.1	$ 413.2
Work in process	2,285.1	751.9
Finished goods	316.1	200.4
Inventory	3,038.3	1,365.5
Inventory, current	2,982.4	1,344.4
Inventory, noncurrent	$ 55.9	$ 21.1

Dispositions (Details Textual) ₩ in Millions, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
Dispositions (Details Textual) ₩ in Millions, $ in Millions	Apr. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 KRW (₩)	Dec. 31, 2022 USD ($)	Mar. 31, 2022
Samsung Bioepis
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity, ownership interest		49.90%	49.90%			49.90%
Equity Method Investment, Amount Sold	$ 2,300.0
Samsung Bioepis \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other current assets, receivable		$ 422.3	$ 422.3		$ 798.8
Samsung Bioepis \| Payment Due At First Anniversary \| Discount rates \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Risk-adjusted discount rates		0.064	0.064
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
Payables to divestiture of interest in joint venture	1,300.0
Investment in Samsung Bioepis \| ₩				₩ 581.6
Gain on sale of equity interest in Samsung Bioepis		$ 1,500.0	$ 1,500.0
Cumulative translation loss			58.9
Gain on derivative used in net investment hedge			57.0
Additional milestone payment	50.0
Samsung Bioepis \| Payment Due At First Anniversary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payables to divestiture of interest in joint venture	812.5
Gain (loss) on sale			13.7
Samsung Bioepis \| Payment Due At Second Anniversary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payables to divestiture of interest in joint venture	$ 437.5
Gain (loss) on sale		$ 7.1	$ 16.9

Accumulated Other Comprehensive Income (Loss) (Tables)

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss)

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


	September 30, 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		18.9		0.6		(11.8)		10.0
Amounts reclassified from AOCI	13.4		(17.8)		—		—		(4.4)
Net current period other comprehensive income (loss)	15.7		1.1		0.6		(11.8)		5.6
Balance, September 30, 2023	$	—	$	16.2	$	(0.5)	$	(175.0)	$	(159.3)


	September 30, 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	(26.4)		204.5		12.6		4.2		(154.5)		40.4
Amounts reclassified from AOCI	7.4		(125.5)		(38.1)		—		58.9		(97.3)
Net current period other comprehensive income (loss)	(19.0)		79.0		(25.5)		4.2		(95.6)		(56.9)
Balance, September 30, 2022	$	(21.2)	$	132.8	$	—	$	(40.6)	$	(234.6)	$	(163.6)

(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 condensed consolidated financial statements.

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 Three Months Ended September 30,				For the Nine Months Ended September 30,
	2023		2022		2023		2022
Gains (losses) on securities available for sale	$	(15.2)	$	(8.0)	$	(17.0)	$	(9.4)	Other (income) expense
	3.2		1.7		3.6		2.0		Income tax (benefit) expense

Gains (losses) on cash flow hedges	(1.7)		77.7		18.3		143.2		Revenue
	1.2		(0.8)		2.1		(3.5)		Operating expense
	(0.1)		—		(0.3)		(0.2)		Other (income) expense
	—		(7.8)		(2.3)		(14.0)		Income tax (benefit) expense

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


Currency translation adjustments	—		—		—		(58.9)		Other (income) expense
Total reclassifications, net of tax	$	(12.6)	$	62.8	$	4.4	$	97.3

Inventory

9 Months Ended

Sep. 30, 2023

Inventory Disclosure [Abstract]

Inventory

The components of inventory are summarized as follows:


(In millions)	As of September 30, 2023		As of December 31, 2022
Raw materials	$	437.1	$	413.2
Work in process	2,285.1		751.9
Finished goods	316.1		200.4
Total inventory	$	3,038.3	$	1,365.5

Balance Sheet Classification:
Inventory	$	2,982.4	$	1,344.4
Investments and other assets	55.9		21.1
Total inventory	$	3,038.3	$	1,365.5

During the third quarter of 2023 we recorded approximately $1.7 billion of acquired inventory 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 condensed consolidated financial statements.

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 condensed consolidated statements of income for the nine months ended September 30, 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 condensed consolidated statements of income for the nine months ended September 30, 2022. As of September 30, 2023 and December 31, 2022, the carrying value of our ADUHELM inventory was immaterial.

Revenues - Other Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Revenues - Other Revenues (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,530.3	$ 2,508.5	$ 7,449.3	$ 7,629.4
Contract manufacturing revenue
Disaggregation of Revenue [Line Items]
Total revenue	252.9	114.2	742.9	242.9
Royalty and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	51.3	15.3	38.3	50.6
Contract manufacturing, royalty and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	$ 304.2	$ 129.5	$ 781.2	$ 293.5

- 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

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+ Details

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Variable Interest Entity [Line Items]
(Gain) loss on equity method investments		$ 0.0	$ 2.6
Percentage of future development costs related to Eisai		45.00%
Deferred tax assets, unrecognized tax benefit		$ 85.0
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities		$ 24.4		$ 27.8
Neurimmune
Variable Interest Entity [Line Items]
Collaboration agreement term		12 years
Research and development costs, percentage		100.00%
Eisai
Variable Interest Entity [Line Items]
Percentage of future development costs related to Eisai	45.00%

- 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

Dispositions	9 Months Ended
Dispositions	Sep. 30, 2023
Divestitures [Abstract]
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. During the second quarter of 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 condensed consolidated statements of income for the nine months ended September 30, 2022. 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 elected the fair value option and measured the payments due to us from Samsung BioLogics at fair value. As of September 30, 2023, the estimated fair value of the remaining second deferred payment using a risk-adjusted discount rate of 6.4% was approximately $422.3 million. This payment has been classified as a Level 3 measurement and is reflected in other current assets within our condensed consolidated balance sheets as of September 30, 2023. For the nine months ended September 30, 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 three and nine months ended September 30, 2023, we recognized gains of approximately $7.1 million and $16.9 million, respectively, to reflect the changes in fair value related to the second deferred payment due to us. These changes were recorded in other (income) expense, net in our condensed 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. For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2022 Form 10-K.

Share-Based Payments (Tables)

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Share-based compensation expense included in condensed consolidated statements of income

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Research and development	$	217.1	$	24.5	$	276.3	$	72.6
Selling, general and administrative	234.9		46.5		333.4		129.3

Subtotal	452.0		71.0		609.7		201.9
Capitalized share-based compensation costs	(2.6)		(2.0)		(8.5)		(7.1)
Share-based compensation expense included in total cost and expense	449.4		69.0		601.2		194.8
Income tax effect	(98.5)		(13.0)		(126.5)		(36.0)
Share-based compensation expense included in net income (loss) attributable to Biogen Inc.	$	350.9	$	56.0	$	474.7	$	158.8

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 condensed consolidated statements of income for the three and nine months ended September 30, 2023. These amounts were associated with the accelerated vesting of stock options and RSUs previously granted to Reata employees and required no future services to vest. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these condensed consolidated financial statements.

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 Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Market stock units	$	0.7	$	4.0	$	4.2	$	11.4
Time-vested restricted stock units	53.4		48.7		175.0		150.4


Performance stock units settled in stock	7.8		10.5		27.1		22.1
Performance stock units settled in cash	0.1		5.4		4.8		7.9
Employee stock purchase plan	2.0		2.4		8.8		10.1
Stock options(1)	1.0		—		2.8		—
Reata equity awards(2)	387.0		—		387.0		—
Subtotal	452.0		71.0		609.7		201.9
Capitalized share-based compensation costs	(2.6)		(2.0)		(8.5)		(7.1)
Share-based compensation expense included in total cost and expense	$	449.4	$	69.0	$	601.2	$	194.8

(1) During the fourth quarter of 2022 we granted stock options. For additional information, please read Note 16, Share-Based Payments, to our consolidated financial statements included in our 2022 Form 10-K.

(2) 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 and required no future services to vest. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these condensed consolidated financial statements.

Collaborative and Other Relationships - Summary of Activity Related to Sage Therapeutics (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2023
Collaborative arrangements and non-collaborative arrangement transactions
Share of net profit from sage therapeutics, Percent	50.00%		50.00%
Collaboration profit sharing/(loss reimbursement)	$ 50.5	$ 45.3	$ 164.5	$ (42.6)
Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Collaboration profit sharing/(loss reimbursement)	5.9		5.9
Sage Therapeutics \| Forecast
Collaborative arrangements and non-collaborative arrangement transactions
Potential future milestone payments commitment to third party					$ 75.0
Research and development \| Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	72.0	40.9	158.9	130.4
Expense reflected within statements of income	36.0	20.5	79.5	65.2
Selling, general and administrative \| Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	54.0	28.5	152.3	69.9
Expense reflected within statements of income	$ 27.0	$ 14.2	$ 76.1	$ 34.9

Condensed Consolidated Statement of Equity Statement - USD ($) shares in Thousands, $ in Millions	Total	Preferred stock	Common stock	Additional paid-in capital	Accumulated Other Comprehensive Income	Retained earnings	Treasury stock	Parent	Noncontrolling interest	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 Parent
Beginning balance, shares at Dec. 31, 2021		0	170,800
Beginning balance at Dec. 31, 2021	$ 10,959.7	$ 0.0	$ 0.1	$ 68.2	$ (106.7)	$ 13,911.7	$ (2,977.1)	$ 10,896.2	$ 63.5
Beginning balance, treasury stock, shares at Dec. 31, 2021							(23,800)
Net income	2,412.1					2,496.5		2,496.5	(84.4)
Other comprehensive income (loss), net of tax	(56.9)				(56.9)			(56.9)
Capital contribution from noncontrolling interest	$ 12.2								12.2
Repurchase of common stock pursuant to the 2020 Share Repurchase Program, at cost (in shares)	(3,600)													(3,600)
Repurchase of common stock pursuant to the 2020 Share Repurchase Program, at cost	$ (750.0)									$ (750.0)				$ (750.0)	$ (750.0)
Retirement of common stock pursuant to the 2020 Share Repurchase Program, at cost (in shares)											(3,600)			(3,600)
Retirement of common stock pursuant to the 2020 Share Repurchase Program, at cost												$ (257.9)	$ (492.1)	$ 750.0
Issuance of common stock under stock option and stock purchase plans, shares			200
Issuance of common stock under stock option and stock purchase plans	37.5			37.5				37.5
Issuance of common stock under award plan, shares			400
Issuance of common stock under stock award plan	(43.2)			(43.2)		0.0		(43.2)
Compensation related to share-based payments	194.1			194.1				194.1
Other	1.3			1.3				1.3
Ending balance at Sep. 30, 2022	12,766.8	$ 0.0	$ 0.1	0.0	(163.6)	15,916.1	$ (2,977.1)	12,775.5	(8.7)
Ending balance, shares at Sep. 30, 2022		0	167,800
Ending balance, treasury stock, shares at Sep. 30, 2022							(23,800)
Beginning balance, shares at Jun. 30, 2022		0	169,000
Beginning balance at Jun. 30, 2022	11,863.4	$ 0.0	$ 0.1	0.0	(110.4)	14,959.9	$ (2,977.1)	11,872.5	(9.1)
Beginning balance, treasury stock, shares at Jun. 30, 2022							(23,800)
Net income	1,134.9					1,134.7		1,134.7	0.2
Other comprehensive income (loss), net of tax	(53.2)				(53.2)			(53.2)
Capital contribution from noncontrolling interest	$ 0.2								0.2
Repurchase of common stock pursuant to the 2020 Share Repurchase Program, at cost (in shares)	(1,200)													(1,200)
Repurchase of common stock pursuant to the 2020 Share Repurchase Program, at cost	$ (250.0)									$ (250.0)				$ (250.0)	$ (250.0)
Retirement of common stock pursuant to the 2020 Share Repurchase Program, at cost (in shares)											(1,200)			(1,200)
Retirement of common stock pursuant to the 2020 Share Repurchase Program, at cost												$ (71.5)	$ (178.5)	$ 250.0
Issuance of common stock under stock option and stock purchase plans, shares			0
Issuance of common stock under stock option and stock purchase plans	8.6			8.6				8.6
Issuance of common stock under award plan, shares			0
Issuance of common stock under stock award plan	(2.8)			(2.8)		0.0		(2.8)
Compensation related to share-based payments	65.7			65.7				65.7
Ending balance at Sep. 30, 2022	12,766.8	$ 0.0	$ 0.1	0.0	(163.6)	15,916.1	$ (2,977.1)	12,775.5	(8.7)
Ending balance, shares at Sep. 30, 2022		0	167,800
Ending balance, treasury stock, shares at Sep. 30, 2022							(23,800)
Beginning balance, shares at Dec. 31, 2022		0	167,900
Beginning balance at Dec. 31, 2022	13,388.4	$ 0.0	$ 0.1	73.3	(164.9)	16,466.5	$ (2,977.1)	13,397.9	(9.5)
Beginning balance, treasury stock, shares at Dec. 31, 2022							(23,800)
Net income	912.6					911.4		911.4	1.2
Other comprehensive income (loss), net of tax	5.6				5.6			5.6
Capital contribution from noncontrolling interest	4.2								4.2
Issuance of common stock under stock option and stock purchase plans, shares			200
Issuance of common stock under stock option and stock purchase plans	38.7			38.7				38.7
Issuance of common stock under award plan, shares			600
Issuance of common stock under stock award plan	(86.7)			(86.7)				(86.7)
Compensation related to share-based payments	217.8			217.8				217.8
Other	(0.9)			(0.9)				(0.9)
Ending balance at Sep. 30, 2023	14,479.7	$ 0.0	$ 0.1	242.2	(159.3)	17,377.9	$ (2,977.1)	14,483.8	(4.1)
Ending balance, shares at Sep. 30, 2023		0	168,700
Ending balance, treasury stock, shares at Sep. 30, 2023							(23,800)
Beginning balance, shares at Jun. 30, 2023		0	168,600
Beginning balance at Jun. 30, 2023	14,460.5	$ 0.0	$ 0.1	170.7	(172.8)	17,446.0	$ (2,977.1)	14,466.9	(6.4)
Beginning balance, treasury stock, shares at Jun. 30, 2023							(23,800)
Net income	(68.3)					(68.1)		(68.1)	(0.2)
Other comprehensive income (loss), net of tax	13.5				13.5			13.5
Capital contribution from noncontrolling interest	2.5								2.5
Issuance of common stock under stock option and stock purchase plans, shares			100
Issuance of common stock under stock option and stock purchase plans	9.3			9.3				9.3
Issuance of common stock under award plan, shares			0
Issuance of common stock under stock award plan	(2.7)			(2.7)				(2.7)
Compensation related to share-based payments	64.8			64.8				64.8
Other	0.1			0.1				0.1
Ending balance at Sep. 30, 2023	$ 14,479.7	$ 0.0	$ 0.1	$ 242.2	$ (159.3)	$ 17,377.9	$ (2,977.1)	$ 14,483.8	$ (4.1)
Ending balance, shares at Sep. 30, 2023		0	168,700
Ending balance, treasury stock, shares at Sep. 30, 2023							(23,800)

Fair Value Measurements (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Fair Value Measurements (Details 2) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration impairment	$ 0.0	$ 2.1	$ 0.0	$ 13.7
Fair Value, Measurements Recurring
Business Acquisition, Contingent Consideration [Line Items]
Fair value, beginning of period		197.5		209.1
Fair value, end of period		$ 195.4		$ 195.4

Revenues - Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Total revenues from anti-CD20 therapeutic programs	$ 2,530.3	$ 2,508.5	$ 7,449.3	$ 7,629.4
Genentech
Disaggregation of Revenue [Line Items]
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	98.9	131.1	315.0	414.2
Other revenues from anti-CD20 therapeutic programs	2.9	4.7	10.6	13.2
Revenue from anti-CD20 therapeutic programs
Disaggregation of Revenue [Line Items]
Total revenues from anti-CD20 therapeutic programs	420.9	416.9	1,253.8	1,252.6
Royalty Attributed To OCREVUS
Disaggregation of Revenue [Line Items]
Total revenues from anti-CD20 therapeutic programs	$ 319.1	$ 281.1	$ 928.2	$ 825.2

- 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

Revenues

9 Months Ended

Sep. 30, 2023

Revenue from Contract with Customer [Abstract]

Revenues

Product Revenue

Revenue by product is summarized as follows:


	For the Three Months Ended September 30,
	2023						2022
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	58.1	$	181.4	$	239.5	$	92.5	$	246.5	$	339.0
VUMERITY	148.8		16.7		165.5		127.9		9.9		137.8
Total Fumarate	206.9		198.1		405.0		220.4		256.4		476.8
AVONEX	148.7		63.5		212.2		174.8		80.3		255.1
PLEGRIDY	31.4		34.1		65.5		39.7		41.2		80.9
Total Interferon	180.1		97.6		277.7		214.5		121.5		336.0
TYSABRI	244.8		211.5		456.3		273.0		232.5		505.5
FAMPYRA	—		20.0		20.0		—		22.0		22.0
Subtotal: MS	631.8		527.2		1,159.0		707.9		632.4		1,340.3

Spinal Muscular Atrophy:
SPINRAZA	150.5		297.7		448.2		140.2		290.9		431.1
Subtotal: SMA	150.5		297.7		448.2		140.2		290.9		431.1

Biosimilars:
BENEPALI	—		112.8		112.8		—		110.2		110.2
IMRALDI	—		54.4		54.4		—		57.7		57.7
FLIXABI	—		20.2		20.2		—		19.0		19.0
BYOOVIZ(1)	6.1		0.8		6.9		0.7		—		0.7
Subtotal: Biosimilars	6.1		188.2		194.3		0.7		186.9		187.6





Other(2)	2.5		1.2		3.7		1.6		1.5		3.1
Total product revenue	$	790.9	$	1,014.3	$	1,805.2	$	850.4	$	1,111.7	$	1,962.1

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

(2) Other includes FUMADERM, ADUHELM and QALSODY, which became commercially available in the U.S. during the second quarter of 2023.


	For the Nine Months Ended September 30,
	2023						2022
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	199.3	$	568.9	$	768.2	$	330.3	$	816.5	$	1,146.8
VUMERITY	372.6		47.3		419.9		383.0		19.6		402.6
Total Fumarate	571.9		616.2		1,188.1		713.3		836.1		1,549.4
AVONEX	397.2		207.7		604.9		493.8		249.6		743.4
PLEGRIDY	95.4		125.4		220.8		114.2		138.2		252.4
Total Interferon	492.6		333.1		825.7		608.0		387.8		995.8
TYSABRI	750.1		662.1		1,412.2		849.4		693.1		1,542.5
FAMPYRA	—		67.5		67.5		—		73.7		73.7
Subtotal: MS	1,814.6		1,678.9		3,493.5		2,170.7		1,990.7		4,161.4

Spinal Muscular Atrophy:
SPINRAZA	453.0		875.6		1,328.6		443.3		891.4		1,334.7
Subtotal: SMA	453.0		875.6		1,328.6		443.3		891.4		1,334.7

Biosimilars:
BENEPALI	—		331.0		331.0		—		340.7		340.7
IMRALDI	—		167.6		167.6		—		172.4		172.4
FLIXABI	—		60.7		60.7		—		62.0		62.0
BYOOVIZ(1)	21.3		1.2		22.5		1.2		—		1.2
Subtotal: Biosimilars	21.3		560.5		581.8		1.2		575.1		576.3





Other(2)	4.4		6.0		10.4		4.5		6.4		10.9
Total product revenue	$	2,293.3	$	3,121.0	$	5,414.3	$	2,619.7	$	3,463.6	$	6,083.3

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

(2) Other includes FUMADERM, ADUHELM and QALSODY, which became commercially available in the U.S. during the second quarter of 2023.

We recognized revenue from two wholesalers accounting for 26.9% and 10.5% of gross product revenue for the three months ended September 30, 2023, and 27.1% and 9.1% of gross product revenue for the nine months ended September 30, 2023.

We recognized revenue from two wholesalers accounting for 26.9% and 10.5% of gross product revenue for the three months ended September 30, 2022, and 26.8% and 10.7% of gross product revenue for the nine months ended September 30, 2022.

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


(In millions)	Discounts		Contractual Adjustments		Returns		Total
Balance, December 31, 2022	$	153.8	$	857.7	$	23.5	$	1,035.0
Current provisions relating to sales in current year	554.1		1,983.6		14.2		2,551.9
Adjustments relating to prior years	0.2		(24.5)		19.9		(4.4)
Payments/credits relating to sales in current year	(410.4)		(1,362.3)		(2.0)		(1,774.7)
Payments/credits relating to sales in prior years	(137.5)		(574.8)		(23.2)		(735.5)
Balance, September 30, 2023	$	160.2	$	879.7	$	32.4	$	1,072.3

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


(In millions)	As of September 30, 2023		As of December 31, 2022
Reduction of accounts receivable	$	131.4	$	143.4
Component of accrued expense and other	940.9		891.6
Total revenue-related reserves	$	1,072.3	$	1,035.0

Revenue from Anti-CD20 Therapeutic Programs

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Royalty revenue on sales of OCREVUS	$	319.1	$	281.1	$	928.2	$	825.2
Biogen’s share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	98.9		131.1		315.0		414.2
Other revenue from anti-CD20 therapeutic programs	2.9		4.7		10.6		13.2
Total revenue from anti-CD20 therapeutic programs	$	420.9	$	416.9	$	1,253.8	$	1,252.6

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

For additional information on our collaboration arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2022 Form 10-K.

Contract Manufacturing, Royalty and Other Revenue

Contract manufacturing, royalty and other revenue is summarized in the table below.


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Contract manufacturing revenue	$	252.9	$	114.2	$	742.9	$	242.9
Royalty and other revenue	51.3		15.3		38.3		50.6
Total contract manufacturing, royalty and other revenue	$	304.2	$	129.5	$	781.2	$	293.5

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, contract manufacturing amounts related to LEQEMBI were recognized in research and development expense within our condensed consolidated income statements.

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 license 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.

During the third quarter of 2023 we recorded a reclassification of $38.7 million in LEQEMBI collaboration costs from other revenue to selling, general and administrative expense within our condensed consolidated statements of income. We determined that this reclassification does not materially impact the current or previously issued condensed consolidated financial statements.

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 condensed 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
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (b)
-Publisher FASB
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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-Name Accounting Standards Codification
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-Subparagraph (c)
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (b)(2)
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-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

9 Months Ended

Sep. 30, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets and Goodwill

Intangible Assets

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


		As of September 30, 2023						As of December 31, 2022
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology	4-28 years	$	11,053.8	$	(5,793.2)	$	5,260.6	$	7,415.3	$	(5,629.2)	$	1,786.1
In-process research and development	Indefinite until commercialization	1,920.0		—		1,920.0		—		—		—
Priority review voucher	Indefinite	100.0		—		100.0		—		—		—
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	13,137.8	$	(5,793.2)	$	7,344.6	$	7,479.3	$	(5,629.2)	$	1,850.1

Amortization and Impairments

Completed Technology

$3.6 billion.

IPR&D Related to Business Combinations

Priority Review Voucher

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

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 September 30, 2023
2023 (remaining three months)	$	75.0
2024	325.0
2025	430.0
2026	440.0
2027	435.0
2028	445.0

Goodwill

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


(In millions)	As of September 30, 2023
Goodwill, December 31, 2022	$	5,749.0
Goodwill resulting from Reata acquisition	1,057.3
Other	1.2
Goodwill, September 30, 2023	$	6,807.5

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

As of September 30, 2023, we had no accumulated impairment losses related to goodwill. Other includes adjustments related to foreign currency exchange rate fluctuations.

Collaborative and Other Relationships - Summary of Activity Related to the UCB Collaboration (Details) - Research and development - UCB Pharma S.A. - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 13.6	$ 18.3	$ 46.2	$ 51.5
Expense reflected within statements of income	$ 6.8	$ 9.1	$ 23.1	$ 25.7

Financial Instruments (Details 2) $ in Millions	Dec. 31, 2022 USD ($)
Summary of Contractual Maturities: Available-for-Sale Securities
Due in one year or less, amortized cost	$ 1,483.3
Due in one year or less, estimated fair value	1,473.5
Due after one year through five years, amortized cost	703.7
Due after one year through five years, estimated fair value	694.4
Due after five years, amortized cost	12.1
Due after five years, estimated fair value	11.3
Marketable debt securities	2,179.2
Amortized Cost	$ 2,199.1

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net income (loss) attributable to Biogen Inc.	$ (68.1)	$ 1,134.7	$ 911.4	$ 2,496.5
Other comprehensive income:
Unrealized gains (losses) on securities available for sale, net of tax	14.5	(1.0)	15.7	(19.0)
Unrealized gains (losses) on cash flow hedges, net of tax	29.6	5.9	1.1	79.0
Gains (losses) on net investment hedges, net of tax	0.0	0.0	0.0	(25.5)
Unrealized gains (losses) on pension benefit obligation, net of tax	(0.1)	1.5	0.6	4.2
Currency translation adjustment	(30.5)	(59.6)	(11.8)	(95.6)
Total other comprehensive income (loss), net of tax	13.5	(53.2)	5.6	(56.9)
Comprehensive income (loss) attributable to Biogen Inc.	(54.6)	1,081.5	917.0	2,439.6
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	(0.2)	0.2	1.2	(84.4)
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	$ (54.8)	$ 1,081.7	$ 918.2	$ 2,355.2

Restructuring, Business Transformation and Other Cost Saving Initiatives (Tables)

9 Months Ended

Sep. 30, 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 Three Months Ended September 30, 2023				For the Nine Months Ended September 30, 2023

(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs		Total
Selling, general and administrative	$	—	$	5.9	$	5.9	$	—	$	17.4	$	17.4
Research and development	—		0.2		0.2		—		0.7		0.7
Restructuring charges	37.7		17.3		55.0		62.6		33.8		96.4
Total charges	$	37.7	$	23.4	$	61.1	$	62.6	$	51.9	$	114.5

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


	For the Three Months Ended September 30,
	2023						2022
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs(1)		Total
Restructuring charges	$	—	$	—	$	—	$	21.6	$	(6.2)	$	15.4
Total charges	$	—	$	—	$	—	$	21.6	$	(6.2)	$	15.4

	For the Nine Months Ended September 30,
	2023						2022
(In millions)	Severance Costs		Accelerated Depreciation and Other Costs		Total		Severance Costs		Accumulated Depreciation and Other Costs(1)		Total
Restructuring charges	$	—	$	2.6	$	2.6	$	110.2	$	13.9	$	124.1
Total charges	$	—	$	2.6	$	2.6	$	110.2	$	13.9	$	124.1

(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.

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:


	Workforce Reductions
(In millions)	2023		2022

Restructuring reserve as of December 31	$	35.9		$	—
Expense	7.1			27.7
Payment	(15.6)			(6.2)
Foreign currency and other adjustments	0.6			—
Restructuring reserve as of March 31	28.0			21.5
Expense	17.8			60.9
Payment	(13.4)			(29.7)
Foreign currency and other adjustments	(0.1)			(0.5)
Restructuring reserve as of June 30	32.3			52.2
Expense	58.7			21.6
Payment	(31.8)			(32.3)
Foreign currency and other adjustments	0.1			(1.3)
Restructuring reserve as of September 30	$	59.3		$	40.2

Intangible Assets and Goodwill (Tables)

9 Months Ended

Sep. 30, 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 September 30, 2023						As of December 31, 2022
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology	4-28 years	$	11,053.8	$	(5,793.2)	$	5,260.6	$	7,415.3	$	(5,629.2)	$	1,786.1
In-process research and development	Indefinite until commercialization	1,920.0		—		1,920.0		—		—		—
Priority review voucher	Indefinite	100.0		—		100.0		—		—		—
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	13,137.8	$	(5,793.2)	$	7,344.6	$	7,479.3	$	(5,629.2)	$	1,850.1

Estimated future amortization for acquired 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 September 30, 2023
2023 (remaining three months)	$	75.0
2024	325.0
2025	430.0
2026	440.0
2027	435.0
2028	445.0

Summary of roll forward of the changes in goodwill

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


(In millions)	As of September 30, 2023
Goodwill, December 31, 2022	$	5,749.0
Goodwill resulting from Reata acquisition	1,057.3
Other	1.2
Goodwill, September 30, 2023	$	6,807.5

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 350
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-Name Accounting Standards Codification
-Section 55
-Paragraph 24
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-URI https://asc.fasb.org//1943274/2147482548/350-20-55-24

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
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-URI https://asc.fasb.org//1943274/2147482573/350-20-50-1

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
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-Section 50
-Paragraph 1
-Subparagraph (b)
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-URI https://asc.fasb.org//1943274/2147482573/350-20-50-1

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
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-URI https://asc.fasb.org//1943274/2147482573/350-20-50-1

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
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-URI https://asc.fasb.org//1943274/2147482573/350-20-50-1A

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482573/350-20-50-2

+ Details

Financial Instruments (Details 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Financial Instruments (Details 3) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities and sales	$ 5,698.6	$ 1,643.2	$ 7,380.8	$ 3,104.7
Realized gains	1.0	0.0	1.4	0.0
Realized losses	$ 16.3	$ 7.9	$ 18.4	$ 9.3

Collaborative and Other Relationships - Eisai (Details) $ in Millions	Sep. 30, 2023 USD ($)
LEQEMBI Collaboration
Collaborative arrangements and non-collaborative arrangement transactions
Payable Due To Termination Agreement	$ 31.0

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2023
Accounting Policies [Abstract]
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 and co-developed two treatments to address a defining pathology of Alzheimer's disease. We are focused on advancing our pipeline in neurology, neuropsychiatry, 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; QALSODY for the treatment of ALS, which was granted accelerated approval by the FDA during the second quarter of 2023; ADUHELM for the treatment of Alzheimer's disease; and FUMADERM for the treatment of severe plaque psoriasis. We have collaborations with Eisai on the commercialization of LEQEMBI for the treatment of Alzheimer's disease, which was granted traditional approval by the FDA in the third quarter of 2023, and Sage on the commercialization of ZURZUVAE for the treatment of PPD. ZURZUVAE was approved by the FDA in the third quarter of 2023, pending DEA scheduling, which was completed in the fourth quarter of 2023. 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. On September 26, 2023, we completed the acquisition of Reata. As a result of this transaction we acquired SKYCLARYS, the first and only drug approved by the FDA for the treatment of Friedreich's Ataxia in adults and adolescents aged 16 years and older. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these condensed consolidated financial statements. We commercialize 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. We also have the exclusive rights to commercialize TOFIDENCE, a tocilizumab biosimilar referencing ACTEMRA, which was approved by the FDA during the third quarter of 2023. We continue to develop the 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 these unaudited condensed consolidated financial statements (condensed consolidated financial statements). For additional information on our collaboration arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to our audited consolidated financial statements included in our 2022 Form 10-K. Basis of Presentation In the opinion of management, our condensed consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair statement of our financial statements for interim periods in accordance with U.S. GAAP. The information included in this quarterly report on Form 10-Q should be read in conjunction with our audited consolidated financial statements and the accompanying notes included in our 2022 Form 10-K. Our accounting policies are described in the Notes to Consolidated Financial Statements in our 2022 Form 10-K and updated, as necessary, in this report. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from our audited financial statements, but does not include all disclosures required by U.S. GAAP. The results of operations for the three and nine months ended September 30, 2023, are not necessarily indicative of the operating results for the full year or for any other subsequent interim period. 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. Consolidation Our condensed consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and certain 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 condensed 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. Use of Estimates The preparation of our condensed 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. Significant Accounting Policies There have been no material changes to our significant accounting policies disclosed in Note 1, Summary of Significant Accounting Policies, to our audited consolidated financial statements included in our 2022 Form 10-K. 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. 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 had or may have a material impact on our condensed consolidated financial statements or 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 becomes 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 condensed consolidated statements of income, as a result of removing the impact of the remaining contractual sale restrictions from the fair value measurement of certain shares in Sage.

Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 88.5	$ 109.3	$ 282.6	$ 264.9
Expense reflected within statements of income	44.3	54.7	141.3	132.5
Selling, general and administrative \| E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	81.7	14.5	95.5	34.2
Expense incurred by the collaboration	$ 163.4	29.0	$ 191.0	68.3
Selling, general and administrative \| ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income		(3.9)		68.1
Expense incurred by the collaboration		$ (8.0)		$ 127.8

Share-Based Payments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
Share-Based Payments (Details) - USD ($) $ in Millions	Sep. 26, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense		$ (64.8)	$ (65.7)	$ (217.8)	$ (194.1)
Subtotal		452.0	71.0	609.7	201.9
Capitalized share-based compensation costs		(2.6)	(2.0)	(8.5)	(7.1)
Share-based compensation expense included in total costs and expenses		449.4	69.0	601.2	194.8
Income tax effect		(98.5)	(13.0)	(126.5)	(36.0)
Selling, General and Administrative Expense		788.2	563.3	1,941.2	1,770.8
Reata Pharmaceuticals, Inc
Share-based Compensation Expense included in consolidated statements of income
Operating expenses	$ 393.4
Selling, General and Administrative Expense	196.4
Research and development expense asset acquired	$ 197.0
Research and development
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense		217.1	24.5	276.3	72.6
Selling, general and administrative
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense		234.9	46.5	333.4	129.3
Total share-based compensation expense, net of tax
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense		$ 350.9	$ 56.0	$ 474.7	$ 158.8

Derivative Instruments

9 Months Ended

Sep. 30, 2023

Derivative Instruments and Hedging Activities Disclosure [Abstract]

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 September 30, 2023 and December 31, 2022, had durations of 1 to 15 months and 1 to 12 months, respectively. 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 condensed 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
(In millions)	As of September 30, 2023		As of December 31, 2022
Euro	$	1,006.5	$	1,495.5
British pound	43.5		162.8
Swiss franc	78.7		—

Canadian dollar	15.4		57.2
Total foreign currency forward contracts and options	$	1,144.1	$	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:



(In millions)	As of September 30, 2023		As of December 31, 2022
Unrealized gains	$	19.0	$	29.9
Unrealized (losses)	(7.5)		(21.3)
Net unrealized gains (losses)	$	11.5	$	8.6

We expect the net unrealized gains of approximately $11.5 million to be settled over the next 15 months, of which approximately $7.9 million of these net unrealized gains are expected 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 September 30, 2023 and December 31, 2022, credit risk did not materially change the fair value of our foreign currency forward contracts and forward currency options.

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


For the Three Months Ended September 30,
Net Gains/(Losses) Reclassified from AOCI into Operating Income					Net Gains/(Losses) Recognized in Operating Income
Location	2023		2022		Location	2023		2022
Revenue	$	(1.7)	$	77.7	Revenue	$	(2.1)	$	6.6
Operating expense	1.2		(0.8)		Operating expense	0.9		(0.1)

For the Nine Months Ended September 30,
Net Gains/(Losses) Reclassified from AOCI into Operating Income					Net Gains/(Losses) Recognized in Operating Income
Location	2023		2022		Location	2023		2022
Revenue	$	18.3	$	143.2	Revenue	$	(1.5)	$	(0.8)
Operating expense	2.1		(3.5)		Operating expense	(2.0)		(0.4)

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

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







For the Nine Months Ended September 30,
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion)	Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing)			Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing)
Location	2022		Location		2022		Location	2022
Gains (losses) on net investment hedges(1)	$	20.4	Gains (losses) on net investment hedges(1)		$	(3.2)	Other (income) expense(1)	$	(4.6)

For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 19, Collaborative and Other Relationships, to these condensed 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 $1,340.8 million and $1,238.8 million as of September 30, 2023 and December 31, 2022, respectively. Net losses of $22.6 million and $28.0 million related to these contracts were recorded as a component of other (income) expense, net for the three

and nine months ended September 30, 2023, respectively, compared to net losses of $36.5 million and $85.8 million, respectively, in the prior year comparative periods.

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 condensed 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 condensed consolidated balance sheets of our outstanding derivative instruments, including those designated as hedging instruments:


(In millions)	Balance Sheet Location	As of September 30, 2023		As of December 31, 2022
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	20.8	$	37.9
	Investments and other assets	3.4		—
Liability derivative instruments	Accrued expense and other	5.4		18.4







Other Derivative Instruments:
Asset derivative instruments	Other current assets	7.0		25.1
Liability derivative instruments	Accrued expense and other	32.1		7.6

Revenues (Tables)

9 Months Ended

Sep. 30, 2023

Revenue from Contract with Customer [Abstract]

Revenues by product

Revenue by product is summarized as follows:


	For the Three Months Ended September 30,
	2023						2022
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	58.1	$	181.4	$	239.5	$	92.5	$	246.5	$	339.0
VUMERITY	148.8		16.7		165.5		127.9		9.9		137.8
Total Fumarate	206.9		198.1		405.0		220.4		256.4		476.8
AVONEX	148.7		63.5		212.2		174.8		80.3		255.1
PLEGRIDY	31.4		34.1		65.5		39.7		41.2		80.9
Total Interferon	180.1		97.6		277.7		214.5		121.5		336.0
TYSABRI	244.8		211.5		456.3		273.0		232.5		505.5
FAMPYRA	—		20.0		20.0		—		22.0		22.0
Subtotal: MS	631.8		527.2		1,159.0		707.9		632.4		1,340.3

Spinal Muscular Atrophy:
SPINRAZA	150.5		297.7		448.2		140.2		290.9		431.1
Subtotal: SMA	150.5		297.7		448.2		140.2		290.9		431.1

Biosimilars:
BENEPALI	—		112.8		112.8		—		110.2		110.2
IMRALDI	—		54.4		54.4		—		57.7		57.7
FLIXABI	—		20.2		20.2		—		19.0		19.0
BYOOVIZ(1)	6.1		0.8		6.9		0.7		—		0.7
Subtotal: Biosimilars	6.1		188.2		194.3		0.7		186.9		187.6





Other(2)	2.5		1.2		3.7		1.6		1.5		3.1
Total product revenue	$	790.9	$	1,014.3	$	1,805.2	$	850.4	$	1,111.7	$	1,962.1

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

(2) Other includes FUMADERM, ADUHELM and QALSODY, which became commercially available in the U.S. during the second quarter of 2023.


	For the Nine Months Ended September 30,
	2023						2022
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	199.3	$	568.9	$	768.2	$	330.3	$	816.5	$	1,146.8
VUMERITY	372.6		47.3		419.9		383.0		19.6		402.6
Total Fumarate	571.9		616.2		1,188.1		713.3		836.1		1,549.4
AVONEX	397.2		207.7		604.9		493.8		249.6		743.4
PLEGRIDY	95.4		125.4		220.8		114.2		138.2		252.4
Total Interferon	492.6		333.1		825.7		608.0		387.8		995.8
TYSABRI	750.1		662.1		1,412.2		849.4		693.1		1,542.5
FAMPYRA	—		67.5		67.5		—		73.7		73.7
Subtotal: MS	1,814.6		1,678.9		3,493.5		2,170.7		1,990.7		4,161.4

Spinal Muscular Atrophy:
SPINRAZA	453.0		875.6		1,328.6		443.3		891.4		1,334.7
Subtotal: SMA	453.0		875.6		1,328.6		443.3		891.4		1,334.7

Biosimilars:
BENEPALI	—		331.0		331.0		—		340.7		340.7
IMRALDI	—		167.6		167.6		—		172.4		172.4
FLIXABI	—		60.7		60.7		—		62.0		62.0
BYOOVIZ(1)	21.3		1.2		22.5		1.2		—		1.2
Subtotal: Biosimilars	21.3		560.5		581.8		1.2		575.1		576.3





Other(2)	4.4		6.0		10.4		4.5		6.4		10.9
Total product revenue	$	2,293.3	$	3,121.0	$	5,414.3	$	2,619.7	$	3,463.6	$	6,083.3

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

(2) Other includes FUMADERM, ADUHELM and QALSODY, which became commercially available in the U.S. during the second quarter of 2023.

Analysis of change In reserves

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


(In millions)	Discounts		Contractual Adjustments		Returns		Total
Balance, December 31, 2022	$	153.8	$	857.7	$	23.5	$	1,035.0
Current provisions relating to sales in current year	554.1		1,983.6		14.2		2,551.9
Adjustments relating to prior years	0.2		(24.5)		19.9		(4.4)
Payments/credits relating to sales in current year	(410.4)		(1,362.3)		(2.0)		(1,774.7)
Payments/credits relating to sales in prior years	(137.5)		(574.8)		(23.2)		(735.5)
Balance, September 30, 2023	$	160.2	$	879.7	$	32.4	$	1,072.3

Total reserves included in consolidated balance sheets

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


(In millions)	As of September 30, 2023		As of December 31, 2022
Reduction of accounts receivable	$	131.4	$	143.4
Component of accrued expense and other	940.9		891.6
Total revenue-related reserves	$	1,072.3	$	1,035.0

Revenues from anti-CD20 therapeutic programs

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Royalty revenue on sales of OCREVUS	$	319.1	$	281.1	$	928.2	$	825.2
Biogen’s share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1)	98.9		131.1		315.0		414.2
Other revenue from anti-CD20 therapeutic programs	2.9		4.7		10.6		13.2
Total revenue from anti-CD20 therapeutic programs	$	420.9	$	416.9	$	1,253.8	$	1,252.6

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

Other revenues


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Contract manufacturing revenue	$	252.9	$	114.2	$	742.9	$	242.9
Royalty and other revenue	51.3		15.3		38.3		50.6
Total contract manufacturing, royalty and other revenue	$	304.2	$	129.5	$	781.2	$	293.5

Financial Instruments (Details Textual)	9 Months Ended
Financial Instruments (Details Textual)	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Average maturity of marketable securities, months	8 months

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Summary of assets and liabilities recorded at fair value

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:


	Fair Value Measurements on a Recurring Basis
	As of September 30, 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	$	1,920.4	$	—	$	1,920.4	$	—




Marketable equity securities	413.6		413.6		—		—
Other current assets:
Receivable from Samsung BioLogics(1)	422.3		—		—		422.3
Derivative contracts	27.8		—		27.8		—
Other non-current assets:
Plan assets for deferred compensation	39.0		—		39.0		—
Derivative contracts	3.4		—		3.4		—
Total	$	2,826.5	$	413.6	$	1,990.6	$	422.3
Liabilities:
Derivative contracts	$	37.5	$	—	$	37.5	$	—

Total	$	37.5	$	—	$	37.5	$	—

(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 condensed 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 condensed consolidated financial statements.


	Fair Value Measurements on a Recurring Basis
	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 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 condensed consolidated financial statements.

Summary of fair and carrying value of debt instruments

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


	As of September 30, 2023				As of December 31, 2022
(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value

4.050% Senior Notes due September 15, 2025	$	1,689.6	$	1,746.2	$	1,699.9	$	1,744.7
2.250% Senior Notes due May 1, 2030	1,196.2		1,493.6		1,219.0		1,492.9
5.200% Senior Notes due September 15, 2045	972.7		1,100.5		1,033.2		1,100.3
3.150% Senior Notes due May 1, 2050	909.2		1,474.2		989.0		1,473.8
3.250% Senior Notes due February 15, 2051	430.8		471.9		469.1		469.3
Total	$	5,198.5	$	6,286.4	$	5,410.2	$	6,281.0

Fair value of 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:


(In millions)	For the Three Months Ended September 30, 2022		For the Nine Months Ended September 30, 2022
Fair value, beginning of period	$	197.5	$	209.1
Changes in fair value	(2.1)		(13.7)

Fair value, end of period	$	195.4	$	195.4

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2023	Nov. 07, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	0-19311
Entity Registrant Name	BIOGEN INC.
Entity Central Index Key	0000875045
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		144,898,112

Collaborative and Other Relationships - ADUHELM Collaboration Agreement (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of future development costs related to Eisai				45.00%
Excess and obsolescence charges related to inventory				$ 62.1	$ 321.6
ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Excess and obsolescence charges related to inventory		$ 275.0	$ 275.0
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
Percentage of future development costs related to Eisai		45.00%
Amounts receivable	$ 34.3			34.3		$ 88.0
Amounts payable	122.6			122.6		$ 81.2
Eisai \| Collaboration profit sharing
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense	$ 3.4			$ 214.0
Eisai \| ADUHELM \| Inventory, Idle Capacity Charges And Contractual Commitments
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense					$ 177.0

Income Taxes

9 Months Ended

Sep. 30, 2023

Income Tax Disclosure [Abstract]

Income Taxes

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 other income tax balances as of September 30, 2023 and December 31, 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 Three Months Ended September 30,				For the Nine Months Ended September 30,
	2023		2022		2023		2022
Statutory rate	21.0	%	21.0	%	21.0	%	21.0	%
State taxes	(1.3)		1.9		1.6		1.1
Taxes on foreign earnings	2.6		(3.4)		(6.1)		(4.4)
Tax credits	24.6		(1.4)		(7.7)		(1.5)
Purchased intangible assets	(2.3)		0.1		0.7		0.2



GILTI	14.8		0.8		(1.7)		0.5



Sale of Samsung Bioepis	—		(0.8)		—		(1.9)
Litigation settlement agreement	—		(1.2)		—		3.1
Neurimmune tax impacts	(0.1)		—		—		2.8
International reorganization	—		—		—		(1.7)
Other, including permanent items	(7.7)		0.2		1.4		0.2
Effective tax rate	51.6	%	17.2	%	9.2	%	19.4	%

The effective tax rate for the three months ended September 30, 2023, reflects a tax benefit of $72.9 million recognized as a result of a pretax loss from operations of $141.2 million recorded during the third quarter of 2023, which was driven, in part, by the impact of the non-cash changes in the value of our equity investments and Reata acquisition-related expenses. For all other periods presented, the effective tax rates reflect tax expense on pretax income from operations in the respective periods.

Changes in Tax Rate

For the three months ended September 30, 2023, compared to the same period in 2022, the change in our effective tax rate was driven by the impact of the non-cash changes in the value of our equity investments and Reata acquisition-related expenses.

For the nine months ended September 30, 2023, compared to the same period in 2022, our effective tax rate, in addition to the items noted above, was also impacted by 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 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 additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these condensed consolidated financial statements.

Accounting for Uncertainty in Income Taxes

We and our subsidiaries are routinely examined by various taxing authorities. 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.

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 $460.0 million, including approximately $450.0 million related to the unrecognized

tax benefits related to Neurimmune's tax basis in ADUHELM, as discussed above, in the next 12 months as a result of various audit closures, settlements and expiration of the statute of limitations. Any changes to our gross unrecognized tax benefits related to Neurimmune's tax basis in ADUHELM would result in a zero net impact to net income attributable to Biogen, Inc., as we have recorded a full valuation allowance against the relevant deferred tax assets.

- 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)
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+ Details

Earnings per Share (Tables)

9 Months Ended

Sep. 30, 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 Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Numerator:
Net income (loss) attributable to Biogen Inc.	$	(68.1)	$	1,134.7	$	911.4	$	2,496.5
Denominator:
Weighted average number of common shares outstanding	144.8		144.4		144.7		145.8
Effect of dilutive securities:

Time-vested restricted stock units	—		0.3		0.7		0.3

Performance stock units settled in stock	—		0.1		0.1		0.1
Dilutive potential common shares	—		0.4		0.8		0.4
Shares used in calculating diluted earnings per share	144.8		144.8		145.5		146.2

Share Repurchases (Details) - USD ($) shares in Thousands	3 Months Ended	9 Months Ended
Share Repurchases (Details) - USD ($) shares in Thousands	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023	Oct. 31, 2020
Class of Stock [Line Items]
Repurchase of common stock, at cost (in shares)	1,200	3,600
Treasury stock, value, acquired, cost method	$ 250,000,000	$ 750,000,000
2020 Share Repurchase Program
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 5,000,000,000
Amount remaining under 2019 Share Repurchase Program			$ 2,100,000,000
Treasury stock, value, acquired, cost method	$ 250,000,000.0	$ 750,000,000.0

- 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.

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+ Details

Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 1,920.4	$ 2,847.6
Commercial paper
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	0.0	177.2
Overnight reverse repurchase agreements
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	0.0	59.0
Money market funds
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	1,920.4	2,581.5
Short-term debt securities
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 0.0	$ 29.9

Income Taxes (Details)	3 Months Ended		9 Months Ended
Income Taxes (Details)	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Statutory rate	21.00%	21.00%	21.00%	21.00%
State taxes	(1.30%)	1.90%	1.60%	1.10%
Taxes on foreign earnings	2.60%	(3.40%)	(6.10%)	(4.40%)
Credits and net operating loss utilization	24.60%	(1.40%)	(7.70%)	(1.50%)
Purchased intangible assets	(2.30%)	0.10%	0.70%	0.20%
GILTI	14.80%	0.80%	(1.70%)	0.50%
Sale of Samsung Bioepis	0.00%	(0.80%)	0.00%	(1.90%)
Litigation settlement agreement	0.00%	(1.20%)	0.00%	3.10%
Neurimmune tax impacts	(0.001)	0	0	0.028
International reorganization	0.00%	0.00%	0.00%	(1.70%)
Other	(7.70%)	0.20%	1.40%	0.20%
Effective tax rate	51.60%	17.20%	9.20%	19.40%

Property, Plant and Equipment	9 Months Ended
Property, Plant and Equipment	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment are recorded at historical cost, net of accumulated depreciation. Accumulated depreciation on property, plant and equipment was $2,342.7 million and $2,165.7 million as of September 30, 2023 and December 31, 2022, respectively. For the three and nine months ended September 30, 2023, depreciation expense totaled $64.1 million and $190.7 million, respectively, compared to $64.2 million and $207.7 million, respectively, in the prior year comparative periods. Solothurn, Switzerland Manufacturing Facility In order to support our future growth and drug development pipeline, we are nearing completion of a large-scale biologics manufacturing facility in Solothurn, Switzerland. This facility will include 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 September 30, 2023 and December 31, 2022, we had approximately $742.0 million and $711.1 million, respectively, capitalized as construction in progress related to this facility. In the second quarter of 2021 a portion of the facility (the first manufacturing suite) received a GMP multi-product license from the SWISSMEDIC and was placed into service. Solothurn has been approved for the manufacture of ADUHELM and LEQEMBI by the FDA. We estimate the second manufacturing suite will be operational by the end of 2023. 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 condensed consolidated statements of income for the three and nine months ended September 30, 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.

Intangible Assets and Goodwill (Details 1)	9 Months Ended
Intangible Assets and Goodwill (Details 1)	Sep. 30, 2023 USD ($)
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	$ 5,749,000,000
Goodwill resulting from Reata acquisition	1,057,300,000
Other	1,200,000
Goodwill, end of period	6,807,500,000
Accumulated impairment losses related to goodwill	$ 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

Collaborative and Other Relationships - Other Arrangements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Research and development	$ 736.3	$ 549.2	$ 1,891.1	$ 1,629.5
Other research and discovery
Collaborative arrangements and non-collaborative arrangement transactions
Research and development	$ 0.0	$ 14.0	$ 2.8	$ 51.5

Financial Instruments Financial Instruments (Details Textual 2) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Other noncurrent assets \| Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio	$ 465.5	$ 846.0

Indebtedness	9 Months Ended
Indebtedness	Sep. 30, 2023
Debt Disclosure [Abstract]
Indebtedness	Credit Agreement In connection with our acquisition of Reata in September 2023 we entered into a $1.5 billion term loan credit agreement. On the closing date of the Reata acquisition we drew $1.0 billion from the 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. As of September 30, 2023, we had $1.0 billion outstanding under the term loan credit agreement, of which $500.0 million was outstanding under the 364-day tranche and $500.0 million outstanding under the three-year tranche. 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 condensed consolidated statements of income for the three and nine months ended September 30, 2022.

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
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+ Details

Inventory (Tables)

9 Months Ended

Sep. 30, 2023

Inventory Disclosure [Abstract]

Components of inventory

The components of inventory are summarized as follows:


(In millions)	As of September 30, 2023		As of December 31, 2022
Raw materials	$	437.1	$	413.2
Work in process	2,285.1		751.9
Finished goods	316.1		200.4
Total inventory	$	3,038.3	$	1,365.5

Balance Sheet Classification:
Inventory	$	2,982.4	$	1,344.4
Investments and other assets	55.9		21.1
Total inventory	$	3,038.3	$	1,365.5

Collaborative and Other Relationships

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborative and Other Relationships


Note 19:			Collaborative and Other Relationships

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 (mosunetuzumab), for the treatment of relapsed or refractory follicular lymphoma, which was granted accelerated approval in the U.S. during the fourth quarter of 2022; COLUMVI (glofitamab), 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.

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.

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.

LUNSUMIO (mosunetuzumab)

In January 2022 we exercised our option with Genentech to participate in the joint development and commercialization of LUNSUMIO. 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. 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 condensed 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.

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.

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%.

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%.

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. This termination fee is included in selling, general and administrative expense in our condensed consolidated statements of income for the nine months ended September 30, 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.

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.

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 condensed consolidated income statements, as we are not the principal.

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	88.5	$	109.3	$	282.6	$	264.9
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	44.3		54.7		141.3		132.5
Total sales and marketing expense incurred by the LEQEMBI Collaboration	163.4		29.0		191.0		68.3
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our condensed consolidated statements of income	81.7		14.5		95.5		34.2

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 and sales and marketing expense related to our initial ADUHELM Collaboration Agreement is as follows:


	For the Three Months Ended September 30,			For the Nine Months Ended September 30,
(In millions)		2022			2022
Total ADUHELM Collaboration development expense		$	34.6		$	116.0
Biogen's share of ADUHELM Collaboration development expense reflected in research and development expense in our condensed consolidated statements of income		19.0			63.8
Total sales and marketing expense incurred by the ADUHELM Collaboration Agreement		(8.0)			127.8
Biogen's share of ADUHELM Collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income		(3.9)			68.1

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 in our condensed consolidated statements of income. We also recorded the related cost of revenue and sales and marketing expense in our condensed 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 condensed consolidated statements of income. For the three and nine months ended September 30, 2022, we recognized net reductions to our operating expense of approximately $3.4 million and $214.0 million, respectively, to reflect Eisai's 45.0% share of net collaboration losses in the U.S.

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 nine months ended September 30, 2022, we recorded approximately $76.0 million 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 nine months ended September 30, 2022.

We recognized approximately $177.0 million related to Eisai's 45.0% share of these charges in collaboration profit sharing/(loss reimbursement) within our condensed consolidated statements of income for the nine months ended September 30, 2022.

Amounts receivable from Eisai related to the agreements discussed above were approximately $34.3 million and $88.0 million as of September 30, 2023 and December 31, 2022, respectively. Amounts payable to Eisai related to the agreements discussed above were $122.6 million and $81.2 million as of September 30, 2023 and December 31, 2022, respectively.

For additional information on our collaboration arrangements with Eisai, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2022 Form 10-K.

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 Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total UCB collaboration development expense	$	13.6	$	18.3	$	46.2	$	51.5
Biogen's share of UCB collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	6.8		9.1		23.1		25.7

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 potential treatment of MDD and PPD and BIIB124 (SAGE-324) for the potential treatment of essential tremor with potential in other neurological conditions such as epilepsy.

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. We expect ZURZUVAE for PPD to be commercially available beginning in 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 reviewing the feedback 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. We will pay Sage a milestone payment of $75.0 million upon the first commercial sale of ZURZUVAE for PPD in the U.S.

For the three and nine months ended September 30, 2023, we recorded $5.9 million to reflect Sage's 50.0% share of net collaboration expense in the U.S. related to commercialization activities to support ZURZUVAE for PPD, which is recognized in collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income.

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total Sage collaboration development expense	$	72.0	$	40.9	$	158.9	$	130.4
Biogen's share of Sage collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	36.0		20.5		79.5		65.2
Total sales and marketing expense incurred by the Sage collaboration	54.0		28.5		152.3		69.9
Biogen's share of Sage collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income	27.0		14.2		76.1		34.9

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 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.

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 agree 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 Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total Denali collaboration development expense	$	12.6	$	19.9	$	51.3	$	58.0
Biogen's share of Denali collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	7.6		11.4		30.8		33.5

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 three and nine months ended September 30, 2023, we recorded zero and $2.8 million, respectively, as research and development expense in our condensed consolidated statements of income related to other research and discovery related arrangements, compared to $14.0 million and $51.5 million, respectively, in the prior year comparative periods.

Samsung Bioepis Co., Ltd.

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%.

In connection with this transaction, we may also pay Samsung Bioepis up to approximately $180.0 million in additional development, regulatory and sales-based milestones.

We also acquired an option to extend the term of our 2013 commercial agreement for BENEPALI, IMRALDI and FLIXABI by an additional five years, subject to payment of an option exercise fee of $60.0 million, and obtained an option to acquire exclusive rights to commercialize these products in China.

2013 Commercial Agreement

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

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 condensed consolidated statements of income. For the three and nine months ended September 30, 2023, we recognized net profit-sharing expense of $56.4 million and $170.4 million, respectively, to reflect Samsung Bioepis' 50.0% sharing of the net collaboration profits, compared to a net profit-sharing expense of $48.7 million and $171.4 million, respectively, in the prior year comparative periods.

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 condensed consolidated statements of income.

Amounts receivable from Samsung Bioepis related to the agreements discussed above were $13.0 million and $2.0 million as of September 30, 2023 and December 31, 2022, respectively. Amounts payable to Samsung Bioepis related to the agreements discussed above were $81.6 million and $40.5 million as of September 30, 2023 and December 31, 2022, respectively.

For additional information on our collaboration arrangements with Samsung Bioepis and our other significant collaboration arrangements, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2022 Form 10-K.

Investments in Variable Interest Entities	9 Months Ended
Investments in Variable Interest Entities	Sep. 30, 2023
Investments in Variable Interest Entities [Abstract]
Investments in Variable Interest Entities	Consolidated Variable Interest Entities Our condensed 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 We have a collaboration and license agreement with Neurimmune for the development and commercialization of antibodies for the potential treatment of Alzheimer's disease, including ADUHELM (as amended, the Neurimmune Agreement). We are responsible for the development, manufacturing and commercialization of all collaboration products. The Neurimmune Agreement is effective for the longer of the duration of certain patents relating to a licensed product or 12 years from the first commercial sale of a licensed product. We consolidate the results of Neurimmune as we determined that we are the primary beneficiary of Neurimmune because we have the power through the collaboration to direct the activities that most significantly impact the entity’s economic performance and we are required to fund 100.0% of the research and development costs incurred in support of the collaboration. Our royalty rates payable on products developed under the Neurimmune Agreement, including royalty rates payable on commercial sales of ADUHELM, range from the high single digits to sub-teens. 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 a previously recorded deferred tax asset to zero. This adjustment to our net deferred tax asset is recorded with an equal and offsetting amount assigned to net income (loss) attributable to noncontrolling interests, net of tax in our condensed 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 condensed 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. 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 September 30, 2023 and December 31, 2022, the carrying value of our investments in certain biotechnology companies representing potential unconsolidated variable interest entities totaled $24.4 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 condensed consolidated statements of income as they are incurred. We have provided no financing to these variable interest entities other than previous contractually required amounts. For additional information on our investments in Neurimmune and other variable interest entities, please read Note 20, Investments in Variable Interest Entities, to our consolidated financial statements included in our 2022 Form 10-K.

Financial Instruments

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

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 condensed consolidated balance sheets:


(In millions)	As of September 30, 2023		As of December 31, 2022
Commercial paper	$	—	$	177.2
Overnight reverse repurchase agreements	—		59.0
Money market funds	1,920.4		2,581.5

Short-term debt securities	—		29.9
Total	$	1,920.4	$	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 September 30, 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 condensed consolidated financial statements.

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


	As of September 30, 2023
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value












Marketable equity securities

Marketable equity securities, non-current	$	993.3	$	—	$	(579.7)	$	413.6
Total marketable equity securities	$	993.3	$	—	$	(579.7)	$	413.6


	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 Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Proceeds from maturities and sales	$	5,698.6	$	1,643.2	$	7,380.8	$	3,104.7
Realized gains	1.0		—		1.4		—
Realized losses	16.3		7.9		18.4		9.3

Realized losses for the three and nine months ended September 30, 2023, primarily relate to sales of U.S. treasuries and corporate bonds. Realized losses for the three and nine months ended September 30, 2022, 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 condensed 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 September 30, 2023 and December 31, 2022, our strategic investment portfolio was comprised of investments totaling $465.5 million and $846.0 million, respectively, which are included in investments and other assets in our condensed consolidated balance sheets.

The decrease in our strategic investment portfolio as of September 30, 2023, was primarily due to the decrease in the fair value of our investments in Denali, Sangamo and Sage common stock. Additionally, we sold a portion of our Sangamo common stock during the third quarter of 2023.

For additional information on our strategic investments in Denali, Sangamo and Sage common stock, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2022 Form 10-K.

Acquisitions

9 Months Ended

Sep. 30, 2023

Business Combinations [Abstract]

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, the first and only drug approved by the FDA 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 condensed consolidated statements of income for the three and nine months ended September 30, 2023. These amounts were associated with the accelerated vesting of stock options and RSUs previously granted to Reata employees and required no future services to vest. Approximately $980.0 million of the $983.9 million payment to the equity award holders was made in October 2023.

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 condensed 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 preliminary purchase price allocation of the separately identifiable assets acquired and liabilities assumed as of September 26, 2023:


(In millions)	As of September 26, 2023
Cash and cash equivalents	$	267.3
Accounts receivable	15.9
Inventory	1,692.0
Other current assets	53.6
Intangible assets:
Completed technology for SKYCLARYS (U.S.)	3,600.0
In-process research and development (omaveloxolone)	1,900.0
Priority review voucher	100.0
Other clinical programs	20.0
Operating lease assets	122.4
Accrued expense and other	(98.9)
Debt payable	(159.9)
Contingent payable to Blackstone(1)	(300.0)
Deferred tax liability	(922.5)
Operating lease liabilities	(151.8)
Other assets and liabilities, net	(2.0)
Total identifiable net assets	6,136.1
Goodwill	1,057.3
Total assets acquired and liabilities assumed	$	7,193.4

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

Inventory: Total inventory acquired was approximately $1.7 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 condensed consolidated statements of income when the inventory is sold, which is expected to be within approximately 3 years from the acquisition date.

Intangible assets: Intangible assets are comprised of $3.6 billion related to SKYCLARYS commercialization rights in the U.S., $1.9 billion of IPR&D related to the omaveloxolone program outside the U.S., $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 $20.0 million related to other clinical programs. The estimated fair values of the program related intangible assets were determined using a probability adjusted discounted cash flow analysis approach utilizing a discount rate of 17.0% and the estimated fair value of the priority review voucher was based on recent external purchase and sale transactions of similar vouchers.

The more significant assumptions utilized in our asset valuations included the estimated net cash flows for each year for each asset or product, including net revenue, cost of sales, research and development and other operating expense, the potential regulatory and commercial success risks, competitive trends impacting the asset and each cash flow stream as well as other factors. Our valuation of the SKYCLARYS commercialization rights reflects the assumption that, using an economic consumption model, the related $3.6 billion intangible asset will be amortized over its expected economic life. Our valuation of the $1.9 billion IPR&D asset related to omaveloxolone, which has been submitted to the EMA and is currently under review, reflects the assumption that, if regulatory approval is obtained, sales would commence in certain countries in Europe during 2024.

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 $122.4 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 $1.1 billion, 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 $26.3 million and are included within selling, general and administrative expense within our condensed consolidated statements of income for the three and nine months ended September 30, 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 condensed 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 intangible assets, inventory, goodwill, leases and 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. The Reata operations had an immaterial impact to our results of operations for the three and nine months ended September 30, 2023, given the proximity of the acquisition date to quarter-end. Due to the immateriality of Reata's revenues and expenses, additional pro forma information combining the results of operations of Biogen and Reata have not been included.

Restructuring, Business Transformation and Other Cost Saving Initiatives - Restructuring Reserve Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended	9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Expense	$ 76.0			$ 15.4			$ 120.0	$ 124.1
2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Expense	61.1						114.5
Severance Costs \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Expense	0.0			21.6			0.0	110.2
Severance Costs \| 2023 and 2022 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, beginning	32.3	$ 28.0	$ 35.9	52.2	$ 0.0	$ 0.0	35.9	0.0
Expense	58.7	17.8	7.1	21.6	27.7	60.9
Payment	(31.8)	(13.4)	(15.6)	(32.3)	(6.2)	(29.7)
Foreign currency and other adjustments	0.1	(0.1)	0.6	(1.3)	0.0	(0.5)
Restructuring reserve, ending	$ 59.3	$ 32.3	$ 28.0	$ 40.2	$ 21.5	$ 52.2	$ 59.3	$ 40.2

- 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

Summary of Significant Accounting Policies (Details)	9 Months Ended
Summary of Significant Accounting Policies (Details)	Sep. 30, 2023 segment
Accounting Policies [Abstract]
Number of reportable segments	1
Interest in subsidiary (less than given percentage)	100.00%

Income Taxes (Tables)

9 Months Ended

Sep. 30, 2023

Income Tax Disclosure [Abstract]

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 Three Months Ended September 30,				For the Nine Months Ended September 30,
	2023		2022		2023		2022
Statutory rate	21.0	%	21.0	%	21.0	%	21.0	%
State taxes	(1.3)		1.9		1.6		1.1
Taxes on foreign earnings	2.6		(3.4)		(6.1)		(4.4)
Tax credits	24.6		(1.4)		(7.7)		(1.5)
Purchased intangible assets	(2.3)		0.1		0.7		0.2



GILTI	14.8		0.8		(1.7)		0.5



Sale of Samsung Bioepis	—		(0.8)		—		(1.9)
Litigation settlement agreement	—		(1.2)		—		3.1
Neurimmune tax impacts	(0.1)		—		—		2.8
International reorganization	—		—		—		(1.7)
Other, including permanent items	(7.7)		0.2		1.4		0.2
Effective tax rate	51.6	%	17.2	%	9.2	%	19.4	%

Restructuring, Business Transformation and Other Cost Saving Initiatives - FIt for Growth Initiative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 76.0	$ 15.4	$ 120.0	$ 124.1
2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	37.7		62.6
Accelerated Depreciation and Other Costs	23.4		51.9
Restructuring charges	61.1		114.5
Selling, general and administrative \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	0.0		0.0
Accelerated Depreciation and Other Costs	5.9		17.4
Restructuring charges	5.9		17.4
Research and development \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	0.0		0.0
Accelerated Depreciation and Other Costs	0.2		0.7
Restructuring charges	0.2		0.7
Restructuring charges \| 2023 Cost Saving Initiatives
Restructuring Cost and Reserve [Line Items]
Severance Costs	37.7		62.6
Accelerated Depreciation and Other Costs	17.3		33.8
Restructuring charges	$ 55.0		$ 96.4

- 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

Litigation (Details) - USD ($) $ in Thousands		1 Months Ended
Litigation (Details) - USD ($) $ in Thousands	Sep. 26, 2023	Oct. 31, 2023	Aug. 31, 2023	Feb. 28, 2023	Sep. 30, 2023	Dec. 31, 2019
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					$ 49,900	$ 200,000
ERISA Class Action Litigaiton
Loss Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party			$ 9,750
Genentech
Loss Contingencies [Line Items]
Brazil tax assessment, including interest and penalties				$ 88,300
Lender Dispute
Loss Contingencies [Line Items]
Brazil tax assessment, including interest and penalties	$ 23,300
Bardoxolone Securities
Loss Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party		$ 45,000

Income Taxes (Details Textual) $ in Millions	Sep. 30, 2023 USD ($)
Income Tax Contingency [Line Items]
Deferred tax assets, unrecognized tax benefit	$ 85.0
Decrease in unrecognized tax benefits is reasonably possible	460.0
ADUHELM
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	$ 450.0

Restructuring, Business Transformation and Other Cost Saving Initiatives - Narrative (Details) $ in Millions		3 Months Ended	9 Months Ended
	Sep. 26, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) Employee
Reata Pharmaceuticals, Inc
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 21.0	$ 21.0
Reata Pharmaceuticals, Inc \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Expected cost		30.0	$ 30.0
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		37.7	$ 62.6
2023 Cost Saving Initiatives \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 37.7	$ 62.6

- 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

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Total revenue	$ 2,530.3	$ 2,508.5	$ 7,449.3	$ 7,629.4
Cost and expenses:
Cost of sales, excluding amortization and impairment of acquired intangible assets	659.6	469.5	1,915.1	1,707.4
Research and development	736.3	549.2	1,891.1	1,629.5
Selling, general and administrative	788.2	563.3	1,941.2	1,770.8
Amortization and impairment of acquired intangible assets	60.9	56.5	164.0	190.9
Collaboration profit sharing/(loss reimbursement)	50.5	45.3	164.5	(42.6)
(Gain) loss on fair value remeasurement of contingent consideration	0.0	(2.1)	0.0	(13.7)
Restructuring charges	76.0	15.4	120.0	124.1
Gain on sale of building	0.0	503.7	0.0	503.7
Other (income) expense, net	300.0	(56.0)	248.2	(221.3)
Total cost and expense	2,671.5	1,137.4	6,444.1	4,641.4
Income (loss) before income tax (benefit) expense and equity in loss of investee, net of tax	(141.2)	1,371.1	1,005.2	2,988.0
Income tax (benefit) expense	(72.9)	236.2	92.6	578.5
Equity in (income) loss of investee, net of tax	0.0	0.0	0.0	(2.6)
Net income (loss)	(68.3)	1,134.9	912.6	2,412.1
Net income (loss) attributable to noncontrolling interests, net of tax	(0.2)	0.2	1.2	(84.4)
Net income (loss) attributable to Biogen Inc.	$ (68.1)	$ 1,134.7	$ 911.4	$ 2,496.5
Net income per share:
Basic earnings (loss) per share attributable to Biogen Inc.	$ (0.47)	$ 7.86	$ 6.30	$ 17.12
Diluted earnings (loss) per share attributable to Biogen Inc.	$ (0.47)	$ 7.84	$ 6.26	$ 17.07
Weighted-average shares used in calculating:
Basic earnings (loss) per share attributable to Biogen Inc.	144,800	144,400	144,700	145,800
Diluted earnings (loss) per share attributable to Biogen Inc.	144,800	144,800	145,500	146,200
Product, net
Total revenue	$ 1,805.2	$ 1,962.1	$ 5,414.3	$ 6,083.3
LEQEMBI Collaboration
Cost and expenses:
Selling, general and administrative	38.7
Revenue from anti-CD20 therapeutic programs
Total revenue	420.9	416.9	1,253.8	1,252.6
Contract manufacturing, royalty and other revenue
Total revenue	$ 304.2	$ 129.5	$ 781.2	$ 293.5

Collaborative and Other Relationships - Profit Sharing (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
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%
After Second GAZYVA Threshold Date	35.00%
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Four	30.00%
GAZYVA
Collaborative arrangements and non-collaborative arrangement transactions
Co-promotion operating profit threshold for Rituxan in US and Canada to determine share of co promotion operating profit prior to amendment	$ 50.0
Until Second GAZYVA Threshold Date	37.50%
After Second GAZYVA Threshold Date	35.00%
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

Collaborative and Other Relationships (Tables)

9 Months Ended

Sep. 30, 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	%

Summary of activity related to Aducanumab collaboration

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


	For the Three Months Ended September 30,			For the Nine Months Ended September 30,
(In millions)		2022			2022
Total ADUHELM Collaboration development expense		$	34.6		$	116.0
Biogen's share of ADUHELM Collaboration development expense reflected in research and development expense in our condensed consolidated statements of income		19.0			63.8
Total sales and marketing expense incurred by the ADUHELM Collaboration Agreement		(8.0)			127.8
Biogen's share of ADUHELM Collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income		(3.9)			68.1

Summary of activity related to the UCB collaboration

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total UCB collaboration development expense	$	13.6	$	18.3	$	46.2	$	51.5
Biogen's share of UCB collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	6.8		9.1		23.1		25.7

Summary of Activity Related to Denali Therapeutics Collaboration

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total Denali collaboration development expense	$	12.6	$	19.9	$	51.3	$	58.0
Biogen's share of Denali collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	7.6		11.4		30.8		33.5

Summary of Activity Related to BAN2401 and Elenbecestat Collaboration


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	88.5	$	109.3	$	282.6	$	264.9
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	44.3		54.7		141.3		132.5
Total sales and marketing expense incurred by the LEQEMBI Collaboration	163.4		29.0		191.0		68.3
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our condensed consolidated statements of income	81.7		14.5		95.5		34.2

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 Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Total Sage collaboration development expense	$	72.0	$	40.9	$	158.9	$	130.4
Biogen's share of Sage collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	36.0		20.5		79.5		65.2
Total sales and marketing expense incurred by the Sage collaboration	54.0		28.5		152.3		69.9
Biogen's share of Sage collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income	27.0		14.2		76.1		34.9

Earnings per Share

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Earnings per Share

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Numerator:
Net income (loss) attributable to Biogen Inc.	$	(68.1)	$	1,134.7	$	911.4	$	2,496.5
Denominator:
Weighted average number of common shares outstanding	144.8		144.4		144.7		145.8
Effect of dilutive securities:

Time-vested restricted stock units	—		0.3		0.7		0.3

Performance stock units settled in stock	—		0.1		0.1		0.1
Dilutive potential common shares	—		0.4		0.8		0.4
Shares used in calculating diluted earnings per share	144.8		144.8		145.5		146.2

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

Fair Value Measurements (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
Fair Value Measurements (Details Textual) - USD ($)	Sep. 30, 2023	Sep. 30, 2023
Debt Instrument [Line Items]
Asset impairment charges	$ 0	$ 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

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+ Details

Collaborative and Other Relationships - Summary of Activity Related to ADUHELM Collaboration (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Selling, general and administrative	$ 788.2	$ 563.3	$ 1,941.2	$ 1,770.8
ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Aggregate gross idle capacity charges			$ 76.0
LEQEMBI Collaboration
Collaborative arrangements and non-collaborative arrangement transactions
Share of non-controling interest recognized	50.00%		50.00%
Selling, general and administrative	$ 38.7
Research and development \| Eisai \| ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration		34.6		116.0
Expense reflected within statements of income		19.0		63.8
Selling, general and administrative \| Eisai \| ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration		(8.0)		127.8
Expense reflected within statements of income		$ (3.9)		$ 68.1

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flow from operating activities:
Net income	$ 912.6	$ 2,412.1
Adjustments to reconcile net income to net cash flow from operating activities:
Depreciation and amortization	354.7	398.6
Excess and obsolescence charges related to inventory	62.1	321.6
Share-based compensation	209.3	186.9
Contingent consideration	0.0	(13.7)
Deferred income taxes	(377.7)	(139.8)
(Gain) loss on strategic investments	275.7	160.3
(Gain) loss on equity method investments	0.0	(2.6)
Gain on sale of equity interest in Samsung Bioepis	0.0	(1,505.4)
Gain on sale of building	0.0	(503.7)
Other	98.6	147.8
Changes in operating assets and liabilities, net:
Inventory	(34.9)	(338.3)
Accrued expense and other current liabilities	293.9	632.3
Income tax assets and liabilities	(114.8)	(100.2)
Other changes in operating assets and liabilities, net	(71.4)	15.9
Net cash flow provided by (used in) operating activities	1,534.7	1,559.3
Cash flows from investing activities:
Purchases of property, plant and equipment	(211.8)	(153.9)
Proceeds from sales and maturities of marketable securities	7,380.8	3,104.7
Purchases of marketable securities	(5,140.7)	(2,805.9)
Acquisition of Reata, net of cash acquired	(6,335.6)	0.0
Proceeds from sale of equity interest in Samsung Bioepis	788.1	990.3
Acquisitions of intangible assets	(34.4)	(1.9)
Proceeds from sales of strategic investments	106.2	0.0
Other	(1.3)	1.8
Net cash flow provided by (used in) investing activities	(3,448.7)	1,717.7
Cash flows from financing activities:
Purchases of treasury stock	0.0	750.0
Payments related to issuance of stock for share-based compensation arrangements, net	(48.0)	(5.8)
Repayment of borrowings and premiums paid	159.9	1,002.2
Proceeds from borrowings, net	997.2	0.0
Net (distribution) contribution to noncontrolling interest	4.2	12.2
Other	1.9	5.9
Net cash flow provided by (used in) financing activities	795.4	(1,739.9)
Net increase (decrease) in cash and cash equivalents	(1,118.6)	1,537.1
Effect of exchange rate changes on cash and cash equivalents	(12.8)	(122.9)
Cash and cash equivalents, beginning of the period	3,419.3	2,261.4
Cash and cash equivalents, end of the period	2,287.9	3,675.6
Nonrelated Party
Changes in operating assets and liabilities, net:
Accounts receivable	(76.5)	(109.5)
Related Party
Changes in operating assets and liabilities, net:
Accounts receivable	$ 3.1	$ (3.0)

Collaborative and Other Relationships - OCREVUS (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2017	Sep. 30, 2023
OCREVUS
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
OCREVUS \| Foreign Tax Authority
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	3.00%
OCREVUS \| Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	13.50%
OCREVUS \| Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	24.00%
Mosunetuzumab
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of future development costs		30.00%

Equity

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Equity

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 1.2 million and 3.6 million shares of our common stock at a cost of approximately $250.0 million and $750.0 million during the three and nine months ended September 30, 2022, respectively. There were no share repurchases of our common stock during the three and nine months ended September 30, 2023. Approximately $2.1 billion remained available under our 2020 Share Repurchase Program as of September 30, 2023.

Accumulated Other Comprehensive Income (Loss)

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


	September 30, 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		18.9		0.6		(11.8)		10.0
Amounts reclassified from AOCI	13.4		(17.8)		—		—		(4.4)
Net current period other comprehensive income (loss)	15.7		1.1		0.6		(11.8)		5.6
Balance, September 30, 2023	$	—	$	16.2	$	(0.5)	$	(175.0)	$	(159.3)


	September 30, 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	(26.4)		204.5		12.6		4.2		(154.5)		40.4
Amounts reclassified from AOCI	7.4		(125.5)		(38.1)		—		58.9		(97.3)
Net current period other comprehensive income (loss)	(19.0)		79.0		(25.5)		4.2		(95.6)		(56.9)
Balance, September 30, 2022	$	(21.2)	$	132.8	$	—	$	(40.6)	$	(234.6)	$	(163.6)

The following table summarizes the amounts reclassified from AOCI:


(In millions)	Amounts Reclassified from AOCI								Income Statement Location
	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2023		2022		2023		2022
Gains (losses) on securities available for sale	$	(15.2)	$	(8.0)	$	(17.0)	$	(9.4)	Other (income) expense
	3.2		1.7		3.6		2.0		Income tax (benefit) expense

Gains (losses) on cash flow hedges	(1.7)		77.7		18.3		143.2		Revenue
	1.2		(0.8)		2.1		(3.5)		Operating expense
	(0.1)		—		(0.3)		(0.2)		Other (income) expense
	—		(7.8)		(2.3)		(14.0)		Income tax (benefit) expense

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


Currency translation adjustments	—		—		—		(58.9)		Other (income) expense
Total reclassifications, net of tax	$	(12.6)	$	62.8	$	4.4	$	97.3

- 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
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

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

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

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Assets:
Marketable debt securities		$ 2,179.2
Derivative contracts	$ 3.4
Samsung Bioepis
Liabilities:
Equity, ownership interest	49.90%				49.90%
Fair Value, Measurements Recurring
Assets:
Cash equivalents	$ 1,920.4	2,847.6
Marketable equity securities	413.6	791.1
Derivative contracts	27.8	63.0
Plan assets for deferred compensation	39.0	32.8
Total	2,826.5	7,117.9
Liabilities:
Derivative contracts	37.5	26.0
Contingent consideration obligations			$ 195.4	$ 197.5		$ 209.1
Total	37.5	26.0
Fair Value, Measurements Recurring \| Samsung Bioepis
Assets:
Other current assets, receivable	422.3	798.8
Other assets, receivable		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	413.6	791.1
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Derivative contracts	0.0
Total	413.6	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:
Other current assets, receivable	0.0	0.0
Other assets, receivable		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	1,920.4	2,847.6
Marketable equity securities	0.0	0.0
Derivative contracts	27.8	63.0
Plan assets for deferred compensation	39.0	32.8
Derivative contracts	3.4
Total	1,990.6	5,122.6
Liabilities:
Derivative contracts	37.5	26.0
Total	37.5	26.0
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements Recurring \| Samsung Bioepis
Assets:
Other current assets, receivable	0.0	0.0
Other assets, receivable		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
Derivative contracts	0.0
Total	422.3	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:
Other current assets, receivable	$ 422.3	798.8
Other assets, receivable		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

Restructuring, Business Transformation and Other Cost Saving Initiatives - Total Charges cost saving initiative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 76.0	$ 15.4	$ 120.0	$ 124.1
Severance Costs \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	21.6	0.0	110.2
Severance Costs \| 2022 Cost Saving Initiative \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	21.6	0.0	110.2
Accelerated Depreciation and Other Costs \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	(6.2)	2.6	13.9
Accelerated Depreciation and Other Costs \| 2022 Cost Saving Initiative \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	(6.2)	2.6	13.9
Gain (Loss) on Termination of Lease		5.3
Workforce Reduction \| 2022 Cost Saving Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.0	15.4	2.6	124.1
Workforce Reduction \| 2022 Cost Saving Initiative \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0.0	$ 15.4	$ 2.6	$ 124.1

- 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

Share-based Payments

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Share-based Payments

Share-based Compensation Expense

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Research and development	$	217.1	$	24.5	$	276.3	$	72.6
Selling, general and administrative	234.9		46.5		333.4		129.3

Subtotal	452.0		71.0		609.7		201.9
Capitalized share-based compensation costs	(2.6)		(2.0)		(8.5)		(7.1)
Share-based compensation expense included in total cost and expense	449.4		69.0		601.2		194.8
Income tax effect	(98.5)		(13.0)		(126.5)		(36.0)
Share-based compensation expense included in net income (loss) attributable to Biogen Inc.	$	350.9	$	56.0	$	474.7	$	158.8

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Market stock units	$	0.7	$	4.0	$	4.2	$	11.4
Time-vested restricted stock units	53.4		48.7		175.0		150.4


Performance stock units settled in stock	7.8		10.5		27.1		22.1
Performance stock units settled in cash	0.1		5.4		4.8		7.9
Employee stock purchase plan	2.0		2.4		8.8		10.1
Stock options(1)	1.0		—		2.8		—
Reata equity awards(2)	387.0		—		387.0		—
Subtotal	452.0		71.0		609.7		201.9
Capitalized share-based compensation costs	(2.6)		(2.0)		(8.5)		(7.1)
Share-based compensation expense included in total cost and expense	$	449.4	$	69.0	$	601.2	$	194.8

We estimate the fair value of our obligations associated with our performance stock units settled in cash at the end of each reporting period through expected settlement. Cumulative adjustments to these obligations are recognized each quarter to reflect changes in the stock price and estimated outcome of the performance-related conditions.

Acquisitions (Tables)

9 Months Ended

Sep. 30, 2023

Business Combinations [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 following table summarizes the preliminary purchase price allocation of the separately identifiable assets acquired and liabilities assumed as of September 26, 2023:


(In millions)	As of September 26, 2023
Cash and cash equivalents	$	267.3
Accounts receivable	15.9
Inventory	1,692.0
Other current assets	53.6
Intangible assets:
Completed technology for SKYCLARYS (U.S.)	3,600.0
In-process research and development (omaveloxolone)	1,900.0
Priority review voucher	100.0
Other clinical programs	20.0
Operating lease assets	122.4
Accrued expense and other	(98.9)
Debt payable	(159.9)
Contingent payable to Blackstone(1)	(300.0)
Deferred tax liability	(922.5)
Operating lease liabilities	(151.8)
Other assets and liabilities, net	(2.0)
Total identifiable net assets	6,136.1
Goodwill	1,057.3
Total assets acquired and liabilities assumed	$	7,193.4

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

Property, Plant and Equipment (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
Property, Plant and Equipment (Details) $ in Millions	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) ft²	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Property, Plant and Equipment [Line Items]
Accumulated depreciation		$ 2,342.7		$ 2,342.7		$ 2,165.7
Depreciation		64.1	$ 64.2	190.7	$ 207.7
Sales price				0.0	582.6
Gain on sale of building		0.0	503.7	0.0	503.7
Property, Plant and Equipment, Net		3,301.6		$ 3,301.6		3,298.6
125 Broadway Building Sale
Property, Plant and Equipment [Line Items]
Sales price	$ 603.0
Gain (Loss) on Disposition of Property Plant Equipment, Tenant Allowance					10.8
Gain on sale of building			503.7		503.7
Property, Plant and Equipment, Net	79.2		79.2		79.2
125 Broadway Building Sale \| 125 Broadway Building
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	72.6		72.6		72.6
125 Broadway Building Sale \| Land
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	1.6		1.6		1.6
125 Broadway Building Sale \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	$ 5.0		$ 5.0		$ 5.0
Biologics Manufacturing
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²				393,000
Warehouse, Utilities and Support Space
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²				290,000
Administrative Space
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²				51,000
Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Construction in progress		$ 742.0		$ 742.0		$ 711.1

Inventory - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Inventory - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Inventory [Line Items]
Excess and obsolescence charges related to inventory			$ 62.1	$ 321.6
(Gain) loss on equity method investments			$ 0.0	$ 2.6
Percentage of future development costs related to Eisai			45.00%
Inventory			$ 3,038.3		$ 1,365.5
Eisai
Inventory [Line Items]
Percentage of future development costs related to Eisai	45.00%
ADUHELM
Inventory [Line Items]
Excess and obsolescence charges related to inventory	$ 275.0	$ 275.0
ADUHELM \| Eisai \| Centers for Medicare and Medicaid Service
Inventory [Line Items]
(Gain) loss on equity method investments			$ 136.0

Other Consolidated Financial Statement (Details Textual) - USD ($) $ in Millions		1 Months Ended	3 Months Ended			9 Months Ended
	Sep. 26, 2023	Oct. 31, 2023	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Litigation settlement agreement			$ 0.0	$ 0.0	$ 900.0	$ 0.0	$ 900.0
Net gains recognized on the increase in fair value of equity securities			297.6	(109.3)		268.3	158.1
Net gains (losses) realized during the period on equity securities			4.4	(0.5)		5.3	0.0
Other long-term liabilities			747.9			747.9		$ 944.2
Accrued income taxes			393.8			393.8		$ 541.7
Reata Pharmaceuticals, Inc
Loss on research and development contracts terminated with Eisai	$ 300.0
Total transaction value	$ 6,602.9
Reata Pharmaceuticals, Inc \| Subsequent Event
Total transaction value		$ 980.0
Ionis, Sangamo, Denali and Sage
Net gains recognized on the increase in fair value of equity securities			$ 295.6	$ 112.5		$ 265.0	198.0
Net gains recognized on the decrease in fair value of equity securities							$ 52.2

Revenues - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
Revenues - Narrative (Details) $ in Millions	Sep. 30, 2023 USD ($) wholesaler	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) wholesaler	Sep. 30, 2022 USD ($)
Disaggregation of Revenue [Line Items]
Number of wholesalers \| wholesaler	2		2
Product revenues	$ 2,530.3	$ 2,508.5	$ 7,449.3	$ 7,629.4
Selling, general and administrative	$ 788.2	$ 563.3	$ 1,941.2	$ 1,770.8
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenues from major distributors	26.90%	26.90%	27.10%	26.80%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenues from major distributors	10.50%	10.50%	9.10%	10.70%
Contract manufacturing, royalty and other revenue
Disaggregation of Revenue [Line Items]
Product revenues	$ 304.2	$ 129.5	$ 781.2	$ 293.5
LEQEMBI Collaboration
Disaggregation of Revenue [Line Items]
Share of non-controling interest recognized	50.00%		50.00%
Selling, general and administrative	$ 38.7

Leases	9 Months Ended
Leases	Sep. 30, 2023
Leases [Abstract]
Leases	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 $122.4 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 condensed 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 condensed 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 condensed 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 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 condensed consolidated statements of income for the three and nine months ended September 30, 2022.

Collaborative and Other Relationships - Samsung Bioepis (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 31, 2019 product	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Collaborative arrangements and non-collaborative arrangement transactions
Collaboration profit sharing/(loss reimbursement)		$ 50.5	$ 45.3	$ 164.5	$ (42.6)
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Collaboration profit sharing/(loss reimbursement)		56.4	$ 48.7	$ 170.4	$ 171.4
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Contingent Commercialized Rights, Number Of Products \| product	2
Expected profit share percentage	45.00%			50.00%
Estimated additional payments upon achievement of development and commercial milestones				$ 180.0
Collaboration agreement term				5 years
Option exercise fee				$ 60.0
Samsung Bioepis \| Related Party
Collaborative arrangements and non-collaborative arrangement transactions
Accounts receivable		13.0		13.0		$ 2.0
Accounts payable		$ 81.6		$ 81.6		$ 40.5

Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	May 31, 2018
Derivatives [Line Items]
Gain (loss) on foreign currency derivative instruments not designated as hedging instruments	$ (22.6)	$ (36.5)	$ (28.0)	$ (85.8)
Gains (losses) on net investment hedges, net of tax	$ 0.0	0.0	$ 0.0	(25.5)
Minimum
Derivatives [Line Items]
Range of durations of foreign currency forward contracts					1 month	1 month
Maximum
Derivatives [Line Items]
Range of durations of foreign currency forward contracts	15 months		15 months		15 months	12 months
Not designated as hedging instrument
Derivatives [Line Items]
Derivative, Notional Amount	$ 1,340.8		$ 1,340.8			$ 1,238.8
Other current assets \| Designated as hedging instrument
Derivatives [Line Items]
Derivative asset, fair value	20.8		20.8			37.9
Other current assets \| Not designated as hedging instrument
Derivatives [Line Items]
Derivative asset, fair value	7.0		7.0			25.1
Other noncurrent assets \| Designated as hedging instrument
Derivatives [Line Items]
Derivative asset, fair value	3.4		3.4			0.0
Accrued expenses and other \| Designated as hedging instrument
Derivatives [Line Items]
Derivative liability, fair value	5.4		5.4			18.4
Accrued expenses and other \| Not designated as hedging instrument
Derivatives [Line Items]
Derivative liability, fair value	32.1		32.1			7.6
Foreign exchange contract \| Designated as hedging instrument
Derivatives [Line Items]
Derivative, Notional Amount	1,144.1		1,144.1			1,715.5
Foreign Exchange Forward
Derivatives [Line Items]
Unrealized Gain on Derivatives			19.0	29.9
Unrealized Loss on Derivatives			(7.5)	(21.3)
Unrealized Gain (Loss) on Derivatives			11.5	8.6
Net Investment Hedging
Derivatives [Line Items]
Gains (losses) on net investment hedges, net of tax				20.4
Gains (losses) on net investment hedge, excluded component				(3.2)
Revenue \| Foreign exchange contract
Derivatives [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(1.7)	77.7	18.3	143.2
Revenue \| Cash flows, revenue \| Foreign exchange contract
Derivatives [Line Items]
Gain on interest rate swap	(2.1)	6.6	(1.5)	(0.8)
Operating expense \| Foreign exchange contract
Derivatives [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	1.2	(0.8)	2.1	(3.5)
Operating expense \| Cash flows, operating expenses \| Foreign exchange contract
Derivatives [Line Items]
Gain on interest rate swap	0.9	$ (0.1)	(2.0)	(0.4)
Other income (expense) \| Net Investment Hedging
Derivatives [Line Items]
Gain (loss) recognized in net income, excluded component				$ (4.6)
Euro \| Foreign exchange contract \| Designated as hedging instrument
Derivatives [Line Items]
Derivative, Notional Amount	1,006.5		1,006.5			1,495.5
Swiss franc \| Foreign exchange contract \| Designated as hedging instrument
Derivatives [Line Items]
Derivative, Notional Amount	43.5		43.5			162.8
Japan, Yen \| Foreign exchange contract \| Designated as hedging instrument
Derivatives [Line Items]
Derivative, Notional Amount	15.4		15.4			57.2
Canadian dollar \| Foreign exchange contract \| Designated as hedging instrument
Derivatives [Line Items]
Derivative, Notional Amount	$ 78.7		$ 78.7			$ 0.0
Samsung Bioepis
Derivatives [Line Items]
Equity, ownership interest	49.90%		49.90%				49.90%
Percentage of stake in entity								5.00%
Short-term derivative
Derivatives [Line Items]
Range of durations of foreign currency forward contracts	12 months		12 months
Gain/Loss on fair value of foreign currency forward contracts	$ 7.9		$ 7.9

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			$ (164.9)	$ (106.7)
Balance, January 1, 2018	$ (159.3)	$ (163.6)	(159.3)	(163.6)
Other comprehensive income (loss), before reclassifications, net of tax			10.0	40.4
Amounts reclassified from accumulated other comprehensive income, net of tax			(4.4)	(97.3)
Other comprehensive income (loss), net of tax	13.5	(53.2)	5.6	(56.9)
Accumulated other comprehensive income (loss), net of tax ending balance	(159.3)	(163.6)	(159.3)	(163.6)
Other comprehensive income (loss), net of tax	13.5	(53.2)	5.6	(56.9)
Gains (losses) on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(15.7)	(2.2)
Balance, January 1, 2018	0.0	(21.2)	0.0	(21.2)
Other comprehensive income (loss), before reclassifications, net of tax			2.3	(26.4)
Amounts reclassified from accumulated other comprehensive income, net of tax			13.4	7.4
Other comprehensive income (loss), net of tax			15.7	(19.0)
Accumulated other comprehensive income (loss), net of tax ending balance	0.0	(21.2)	0.0	(21.2)
Gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			15.1	53.8
Balance, January 1, 2018	16.2	132.8	16.2	132.8
Other comprehensive income (loss), before reclassifications, net of tax			18.9	204.5
Amounts reclassified from accumulated other comprehensive income, net of tax			(17.8)	(125.5)
Other comprehensive income (loss), net of tax			1.1	79.0
Accumulated other comprehensive income (loss), net of tax ending balance	16.2	132.8	16.2	132.8
Gains (losses) on net investment hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance				25.5
Balance, January 1, 2018		0.0		0.0
Other comprehensive income (loss), before reclassifications, net of tax				12.6
Amounts reclassified from accumulated other comprehensive income, net of tax				(38.1)
Other comprehensive income (loss), net of tax				(25.5)
Accumulated other comprehensive income (loss), net of tax ending balance		0.0		0.0
Unfunded status of postretirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(1.1)	(44.8)
Balance, January 1, 2018	(0.5)	(40.6)	(0.5)	(40.6)
Other comprehensive income (loss), before reclassifications, net of tax			0.6	4.2
Amounts reclassified from accumulated other comprehensive income, net of tax			0.0	0.0
Other comprehensive income (loss), net of tax			0.6	4.2
Accumulated other comprehensive income (loss), net of tax ending balance	(0.5)	(40.6)	(0.5)	(40.6)
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance			(163.2)	(139.0)
Balance, January 1, 2018	(175.0)	(234.6)	(175.0)	(234.6)
Other comprehensive income (loss), before reclassifications, net of tax			(11.8)	(154.5)
Amounts reclassified from accumulated other comprehensive income, net of tax			0.0	58.9
Other comprehensive income (loss), net of tax			(11.8)	(95.6)
Accumulated other comprehensive income (loss), net of tax ending balance	$ (175.0)	$ (234.6)	$ (175.0)	$ (234.6)

Indebtedness (Details) - USD ($) $ in Thousands	1 Months Ended
Indebtedness (Details) - USD ($) $ in Thousands	Jul. 31, 2022	Sep. 30, 2023	Sep. 26, 2023	Sep. 15, 2022	Sep. 15, 2015
Debt Instrument [Line Items]
Face amount					$ 1,000,000
Redemption rate				99.92%
Senior notes interest rate		3.625%
Extinguishment of debt, amount	$ 2,400
Credit Facility Floating Rate 364-Day Tranche \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 500,000	$ 500,000
The Credit Facility Floating Rate Three-Year Tranche \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		500,000	500,000
The Credit Facility, Terminated \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			500,000
The Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,000,000	1,500,000
The Credit Facility \| Line of Credit \| Secured Debt \| Reata Pharmaceuticals, Inc
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,000,000

Litigation	9 Months Ended
Litigation	Sep. 30, 2023
Loss Contingency, Information about Litigation Matters [Abstract]
Litigation	We are currently involved in various claims 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 our consolidated financial statements included in our 2022 Form 10-K. 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 had been 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 District 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 has been set for December 2023. No hearing has been set in the French action. The EP '488 Patent is the subject of opposition proceedings in the EPO and a hearing before the EPO's Technical Boards of Appeal is set for June 2024. 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. No trial date has been set. 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 August 2023 the court preliminarily approved a settlement under which we agree to pay $9.75 million without any admission of liability. The court has set a hearing for January 2024 to determine whether to grant final approval. Humana Patient Assistance Litigation In March 2023 the 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 April 2023 Humana filed a motion to alter the judgment and amend the complaint, which is pending. Distributor Matter In December 2022 we terminated our distribution agreement with the distributor of products for Biogen in various countries in the Middle East and northern Africa. The former distributor has asserted breach of contract. No suit has been filed. 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. No trial date has been set. 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, subject to approval by the court, providing for payment by Reata of $45.0 million without any admission of liability. 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 its loan agreement with Reata. Other Matters Government Investigation The Company has received subpoenas from the Securities and Exchange Commission seeking information relating to ADUHELM, including healthcare sites and ADUHELM’s approval. 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. The trial has been set for May 2025. 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 (the General Court) 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. No hearing has been set. 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. No trial date has been set. 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.

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
Business Combination, Consideration Transferred, Equity Compensation Pre-acquisition Services	590.5
Consideration transferred	$ 7,193.4
Price per share \| $ / shares	$ 172.50
Number of common stock shares acquired \| shares	38,300

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
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 and co-developed two treatments to address a defining pathology of Alzheimer's disease. We are focused on advancing our pipeline in neurology, neuropsychiatry, 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; QALSODY for the treatment of ALS, which was granted accelerated approval by the FDA during the second quarter of 2023; ADUHELM for the treatment of Alzheimer's disease; and FUMADERM for the treatment of severe plaque psoriasis. We have collaborations with Eisai on the commercialization of LEQEMBI for the treatment of Alzheimer's disease, which was granted traditional approval by the FDA in the third quarter of 2023, and Sage on the commercialization of ZURZUVAE for the treatment of PPD. ZURZUVAE was approved by the FDA in the third quarter of 2023, pending DEA scheduling, which was completed in the fourth quarter of 2023. 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. On September 26, 2023, we completed the acquisition of Reata. As a result of this transaction we acquired SKYCLARYS, the first and only drug approved by the FDA for the treatment of Friedreich's Ataxia in adults and adolescents aged 16 years and older. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these condensed consolidated financial statements. We commercialize 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. We also have the exclusive rights to commercialize TOFIDENCE, a tocilizumab biosimilar referencing ACTEMRA, which was approved by the FDA during the third quarter of 2023. We continue to develop the 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 these unaudited condensed consolidated financial statements (condensed consolidated financial statements). For additional information on our collaboration arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to our audited consolidated financial statements included in our 2022 Form 10-K.
Basis of presentation	In the opinion of management, our condensed consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair statement of our financial statements for interim periods in accordance with U.S. GAAP. The information included in this quarterly report on Form 10-Q should be read in conjunction with our audited consolidated financial statements and the accompanying notes included in our 2022 Form 10-K. Our accounting policies are described in the Notes to Consolidated Financial Statements in our 2022 Form 10-K and updated, as necessary, in this report. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from our audited financial statements, but does not include all disclosures required by U.S. GAAP. The results of operations for the three and nine months ended September 30, 2023, are not necessarily indicative of the operating results for the full year or for any other subsequent interim period. 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.
Consolidation	Our condensed consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and certain 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 condensed 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.
Use of estimates	The preparation of our condensed 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. Significant Accounting Policies There have been no material changes to our significant accounting policies disclosed in Note 1, Summary of Significant Accounting Policies, to our audited consolidated financial statements included in our 2022 Form 10-K. 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. 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 had or may have a material impact on our condensed consolidated financial statements or 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 becomes 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 condensed consolidated statements of income, as a result of removing the impact of the remaining contractual sale restrictions from the fair value measurement of certain shares in Sage.

Revenues Reserves for Discounts and Allowances (Details 1) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 1,035.0
Current Provisions Relating To Sales In Current Year	2,551.9
Adjustments Relating To Prior Years	(4.4)
Payments/Returns Relating To Sales in Current Year	(1,774.7)
Payments/Returns Relating To Sales in Prior Year	(735.5)
Ending Balance	1,072.3
Discounts
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	153.8
Current Provisions Relating To Sales In Current Year	554.1
Adjustments Relating To Prior Years	0.2
Payments/Returns Relating To Sales in Current Year	(410.4)
Payments/Returns Relating To Sales in Prior Year	(137.5)
Ending Balance	160.2
Contractual adjustments
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	857.7
Current Provisions Relating To Sales In Current Year	1,983.6
Adjustments Relating To Prior Years	(24.5)
Payments/Returns Relating To Sales in Current Year	(1,362.3)
Payments/Returns Relating To Sales in Prior Year	(574.8)
Ending Balance	879.7
Returns
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	23.5
Current Provisions Relating To Sales In Current Year	14.2
Adjustments Relating To Prior Years	19.9
Payments/Returns Relating To Sales in Current Year	(2.0)
Payments/Returns Relating To Sales in Prior Year	(23.2)
Ending Balance	$ 32.4

Derivative Instruments (Tables)

9 Months Ended

Sep. 30, 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
(In millions)	As of September 30, 2023		As of December 31, 2022
Euro	$	1,006.5	$	1,495.5
British pound	43.5		162.8
Swiss franc	78.7		—

Canadian dollar	15.4		57.2
Total foreign currency forward contracts and options	$	1,144.1	$	1,715.5

Summary of the effect of cash flow derivatives designated as hedging instruments on the condensed consolidated statements of income

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


For the Three Months Ended September 30,
Net Gains/(Losses) Reclassified from AOCI into Operating Income					Net Gains/(Losses) Recognized in Operating Income
Location	2023		2022		Location	2023		2022
Revenue	$	(1.7)	$	77.7	Revenue	$	(2.1)	$	6.6
Operating expense	1.2		(0.8)		Operating expense	0.9		(0.1)

For the Nine Months Ended September 30,
Net Gains/(Losses) Reclassified from AOCI into Operating Income					Net Gains/(Losses) Recognized in Operating Income
Location	2023		2022		Location	2023		2022
Revenue	$	18.3	$	143.2	Revenue	$	(1.5)	$	(0.8)
Operating expense	2.1		(3.5)		Operating expense	(2.0)		(0.4)

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 condensed consolidated financial statements:







For the Nine Months Ended September 30,
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion)	Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing)			Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing)
Location	2022		Location		2022		Location	2022
Gains (losses) on net investment hedges(1)	$	20.4	Gains (losses) on net investment hedges(1)		$	(3.2)	Other (income) expense(1)	$	(4.6)

Summary of fair value and presentation of derivatives


(In millions)	Balance Sheet Location	As of September 30, 2023		As of December 31, 2022
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	20.8	$	37.9
	Investments and other assets	3.4		—
Liability derivative instruments	Accrued expense and other	5.4		18.4







Other Derivative Instruments:
Asset derivative instruments	Other current assets	7.0		25.1
Liability derivative instruments	Accrued expense and other	32.1		7.6

Derivative Instruments, Unrealized Gain (Loss)

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:



(In millions)	As of September 30, 2023		As of December 31, 2022
Unrealized gains	$	19.0	$	29.9
Unrealized (losses)	(7.5)		(21.3)
Net unrealized gains (losses)	$	11.5	$	8.6

Intangible Assets and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 26, 2023	Dec. 31, 2022
Intangible assets
Total intangible assets, gross	$ 13,137.8		$ 13,137.8			$ 7,479.3
Accumulated Amortization	(5,793.2)		(5,793.2)			(5,629.2)
Intangible assets, net	7,344.6		7,344.6			1,850.1
Amortization and impairment of acquired intangible assets	60.9	$ 56.5	164.0	$ 190.9
Expected future amortization expense, 2023 (remaining three months)	75.0		75.0
Expected future amortization expense, 2024	325.0		325.0
Expected future amortization expense, 2025	430.0		430.0
Expected future amortization expense, 2026	440.0		440.0
Expected future amortization expense, 2027	435.0		435.0
Expected future amortization expense, 2028	445.0		445.0
Completed technology
Intangible assets
Cost	11,053.8		11,053.8			7,415.3
Net	5,260.6		5,260.6			1,786.1
Accumulated Amortization	$ (5,793.2)		$ (5,793.2)			(5,629.2)
Completed technology \| Minimum
Intangible assets
Useful life	4 years		4 years
Completed technology \| Maximum
Intangible assets
Useful life	28 years		28 years
Completed technology for SKYCLARYS (U.S.) \| Reata Pharmaceuticals, Inc
Intangible assets
Intangible assets:					$ 3,600.0
Trademarks and Trade Names
Intangible assets
Cost and Net	$ 64.0		$ 64.0			64.0
Indefinite-lived Intangible Assets (Excluding Goodwill)	64.0		64.0			64.0
In-process research and development
Intangible assets
Cost and Net	1,920.0		1,920.0			0.0
Indefinite-lived Intangible Assets (Excluding Goodwill)	1,920.0		1,920.0			$ 0.0
Priority review voucher
Intangible assets
Cost and Net	100.0		100.0
Indefinite-lived Intangible Assets (Excluding Goodwill)	$ 100.0		$ 100.0

Revenues- Reserves for Discounts and Allowances (Details 2) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Total Reserves	$ 1,072.3	$ 1,035.0
Reduction of accounts receivable
Total Reserves	131.4	143.4
Component of accrued expenses and other
Total Reserves	$ 940.9	$ 891.6

Leases (Details Textual) $ in Millions	1 Months Ended
Leases (Details Textual) $ in Millions	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 26, 2023 USD ($) ft²	Dec. 31, 2022 USD ($)
Operating Leased Assets [Line Items]
Operating lease assets		$ 460.9		$ 403.9
Right-of-use assets derecognized	$ 47.4
Lease liabilities derecognized	52.7
Gain due to lease termination	$ 5.3
125 Broadway Building
Operating Leased Assets [Line Items]
Lease term	5 years 6 months
Operating lease assets		168.2
Operating lease liabilities		$ 168.2
Reata Pharmaceuticals, Inc
Operating Leased Assets [Line Items]
Operating Lease Area \| ft²			327,400
Lease term			16 years
Operating lease liabilities			$ 151.8
Lessee, Operating Lease, Remaining Lease Term			15 years
Operating lease assets			$ 122.4

Reclassification out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	$ (300.0)	$ 56.0	$ (248.2)	$ 221.3
Income Tax Expense (Benefit)	(72.9)	236.2	92.6	578.5
Product revenues	2,530.3	2,508.5	7,449.3	7,629.4
Net income (loss) attributable to Biogen Inc.	$ (68.1)	1,134.7	$ 911.4	2,496.5
Samsung Bioepis
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Equity, ownership interest	49.90%		49.90%		49.90%
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income (loss) attributable to Biogen Inc.	$ (12.6)	62.8	$ 4.4	97.3
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	(15.2)	(8.0)	(17.0)	(9.4)
Income Tax Expense (Benefit)	3.2	1.7	3.6	2.0
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	(0.1)	0.0	(0.3)	(0.2)
Income Tax Expense (Benefit)	0.0	(7.8)	(2.3)	(14.0)
Product revenues	(1.7)	77.7	18.3	143.2
Operating Expenses	1.2	(0.8)	2.1	(3.5)
Gains (losses) on net investment hedge \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	0.0	0.0	0.0	38.1
Currency translation adjustments \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	$ 0.0	$ 0.0	$ 0.0	$ (58.9)

Acquisitions (Details Textual) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended			9 Months Ended
	Sep. 26, 2023 USD ($) ft² $ / shares	Oct. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Business Acquisition [Line Items]
Selling, general and administrative				$ 788.2	$ 563.3	$ 1,941.2	$ 1,770.8
Goodwill				6,807.5		6,807.5		$ 5,749.0
Forecast
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross, Outstanding Equity Awards			$ 983.9
Reata Pharmaceuticals, Inc
Business Acquisition [Line Items]
Price per share \| $ / shares	$ 172.50
Consideration transferred	$ 7,193.4
Total transaction value	6,602.9
Selling, general and administrative	196.4
Research and development expense asset acquired	197.0
Operating expenses	393.4
Inventory	1,692.0
Operating lease liabilities	151.8
Operating lease assets	$ 122.4
Lease term	16 years
Operating Lease Area \| ft²	327,400
Lessee, Operating Lease, Remaining Lease Term	15 years
Fair Value Indefinite Lived Intangible Assets Discount Rate	17.00%
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory Amortization Period	3 years
Goodwill	$ 1,057.3
Business Combination, Consideration Transferred, Equity Compensation Pre-acquisition Services	590.5
Reata Pharmaceuticals, Inc \| Selling, general and administrative
Business Acquisition [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed				$ 26.3		$ 26.3
Reata Pharmaceuticals, Inc \| Completed technology for SKYCLARYS (U.S.)
Business Acquisition [Line Items]
Intangible assets:	3,600.0
Reata Pharmaceuticals, Inc \| In-process research and development
Business Acquisition [Line Items]
Intangible assets:	1,900.0
Reata Pharmaceuticals, Inc \| Priority review voucher
Business Acquisition [Line Items]
Intangible assets:	100.0
Reata Pharmaceuticals, Inc \| Other clinical programs
Business Acquisition [Line Items]
Intangible assets:	$ 20.0
Reata Pharmaceuticals, Inc \| Subsequent Event
Business Acquisition [Line Items]
Total transaction value		$ 980.0

Other Consolidated Financial Statement Detail

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Other Consolidated Financial Statement Detail

Other (Income) Expense, Net

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Gain on sale of equity interest in Samsung Bioepis(1)	$	—	$	—	$	—	$	(1,505.4)
Litigation settlement agreement	—		—		—		900.0
Interest income	(95.9)		(23.9)		(252.7)		(39.4)
Interest expense	63.8		59.9		175.4		191.8
(Gains) losses on investments, net	317.3		(101.8)		289.6		167.5
Foreign exchange (gains) losses, net	11.4		11.5		30.8		39.0
Other, net	3.4		(1.7)		5.1		25.2
Total other (income) expense, net	$	300.0	$	(56.0)	$	248.2	$	(221.3)

(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 condensed 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 condensed consolidated statements of income for the nine months ended September 30, 2022.

The following table summarizes our (gains) losses on investments, net that relate to our equity securities held during the following periods:


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Net (gains) losses recognized on equity securities	$	302.0	$	(109.8)	$	273.6	$	158.1
Less: Net (gains) losses realized on equity securities	4.4		(0.5)		5.3		—
Net unrealized (gains) losses recognized on equity securities	$	297.6	$	(109.3)	$	268.3	$	158.1

The net unrealized losses recognized during the three months ended September 30, 2023, primarily reflect a decrease in the aggregate fair value of our investments in Sage, Denali and Sangamo common stock of approximately $295.6 million.

The net unrealized gains recognized during the three months ended September 30, 2022, primarily reflect an increase in the aggregate fair value of our investments in Sage, Ionis, Sangamo and Denali common stock of approximately $112.5 million.

The net unrealized losses recognized during the nine months ended September 30, 2023, primarily reflect a decrease in the aggregate fair value of our investments in Sage, Denali, Sangamo and Ionis common stock of approximately $265.0 million.

The net unrealized losses recognized during the nine months ended September 30, 2022, primarily reflect a decrease in the aggregate fair value of our investments in Denali and Sangamo common stock of approximately $198.0 million, partially offset by an increase in the fair value of Ionis and Sage common stock of approximately $52.2 million.

Accrued Expense and Other

Accrued expense and other consists of the following:


(In millions)	As of September 30, 2023		As of December 31, 2022
Reata acquisition-related accrued expense	$	1,407.0	$	—
Revenue-related reserves for discounts and allowances	940.9		891.6
Employee compensation and benefits	276.7		395.6
Collaboration expense	298.3		277.9
Royalties and licensing fees	202.8		209.4


Other	712.7		746.9
Total accrued expense and other	$	3,838.4	$	2,521.4

Reata Acquisition-Related Accrued Expense

In connection with our acquisition of Reata we accrued approximately $983.9 million related to Reata's outstanding equity awards, inclusive of employer taxes, of which approximately $980.0 million was subsequently paid in October 2023. As of September 30, 2023, this amount was included within accrued expense and other within our condensed consolidated balance sheets. Additionally, we assumed a payable to Blackstone of approximately $300.0 million related to a one-time contract termination fee to eliminate potential future royalty obligations related to SKYCLARYS, which was triggered as part of the change in control provision under Reata's funding agreement with Blackstone. Payment to Blackstone is expected to be made in November 2023. For additional information on our acquisition of Reata, please read Note 2, Acquisitions, to these condensed consolidated financial statements.

Other Long-term Liabilities

Other long-term liabilities were $747.9 million and $944.2 million as of September 30, 2023 and December 31, 2022, respectively, and included accrued income taxes totaling $393.8 million and $541.7 million, respectively.

Acquisitions Preliminaty Purchase Price Allocation (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 26, 2023	Dec. 31, 2022
Business Acquisition [Line Items]
Goodwill	$ 6,807.5		$ 5,749.0
Reata Pharmaceuticals, Inc
Business Acquisition [Line Items]
Cash and cash equivalents		$ 267.3
Accounts receivable		15.9
Inventory		1,692.0
Other current assets		53.6
Operating lease assets		122.4
Accrued expense and other		(98.9)
Debt payable		(159.9)
Contingent payable to Blackstone(1)		(300.0)
Deferred tax liability		(922.5)
Operating lease liabilities		(151.8)
Other assets and liabilities, net		(2.0)
Total identifiable net assets		6,136.1
Goodwill		1,057.3
Total assets acquired and liabilities assumed		7,193.4
Reata Pharmaceuticals, Inc \| Completed technology for SKYCLARYS (U.S.)
Business Acquisition [Line Items]
Intangible assets:		3,600.0
Reata Pharmaceuticals, Inc \| In-process research and development
Business Acquisition [Line Items]
Intangible assets:		1,900.0
Reata Pharmaceuticals, Inc \| Priority review voucher
Business Acquisition [Line Items]
Intangible assets:		100.0
Reata Pharmaceuticals, Inc \| Other clinical programs
Business Acquisition [Line Items]
Intangible assets:		$ 20.0

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 2,287.9	$ 3,419.3
Marketable securities	0.0	1,473.5
Inventory	2,982.4	1,344.4
Other current assets	974.1	1,417.6
Total current assets	8,454.1	9,791.2
Marketable securities	0.1	705.7
Property, plant and equipment, net	3,301.6	3,298.6
Operating lease assets	460.9	403.9
Intangible assets, net	7,344.6	1,850.1
Goodwill	6,807.5	5,749.0
Deferred tax asset	1,069.8	1,226.4
Investments and other assets	754.6	1,529.2
Total assets	28,193.2	24,554.1
Current liabilities:
Current portion of term loan	500.0	0.0
Taxes payable	243.8	259.9
Accounts payable	440.1	491.5
Accrued expense and other	3,838.4	2,521.4
Total current liabilities	5,022.3	3,272.8
Notes payable and term loan	6,786.4	6,281.0
Deferred tax liability	728.1	334.7
Long-term operating lease liabilities	428.8	333.0
Other long-term liabilities	747.9	944.2
Total liabilities	13,713.5	11,165.7
Commitments, contingencies and guarantees
Biogen Idec 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	242.2	73.3
Accumulated other comprehensive income (loss)	(159.3)	(164.9)
Retained earnings	17,377.9	16,466.5
Treasury stock, at cost	(2,977.1)	(2,977.1)
Total Biogen Inc. shareholders’ equity	14,483.8	13,397.9
Noncontrolling interests	(4.1)	(9.5)
Total equity	14,479.7	13,388.4
Total liabilities and equity	28,193.2	24,554.1
Nonrelated Party
Current assets:
Accounts receivable, net	1,781.4	1,705.0
Related Party
Current assets:
Accounts receivable, net	$ 428.3	$ 431.4

Other Consolidated Financial Statement Detail (Tables)

9 Months Ended

Sep. 30, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Other income (expense), net

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Gain on sale of equity interest in Samsung Bioepis(1)	$	—	$	—	$	—	$	(1,505.4)
Litigation settlement agreement	—		—		—		900.0
Interest income	(95.9)		(23.9)		(252.7)		(39.4)
Interest expense	63.8		59.9		175.4		191.8
(Gains) losses on investments, net	317.3		(101.8)		289.6		167.5
Foreign exchange (gains) losses, net	11.4		11.5		30.8		39.0
Other, net	3.4		(1.7)		5.1		25.2
Total other (income) expense, net	$	300.0	$	(56.0)	$	248.2	$	(221.3)

Gain (loss) on investments in equity securities

The following table summarizes our (gains) losses on investments, net that relate to our equity securities held during the following periods:


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Net (gains) losses recognized on equity securities	$	302.0	$	(109.8)	$	273.6	$	158.1
Less: Net (gains) losses realized on equity securities	4.4		(0.5)		5.3		—
Net unrealized (gains) losses recognized on equity securities	$	297.6	$	(109.3)	$	268.3	$	158.1

Accrued expenses and other

Accrued expense and other consists of the following:


(In millions)	As of September 30, 2023		As of December 31, 2022
Reata acquisition-related accrued expense	$	1,407.0	$	—
Revenue-related reserves for discounts and allowances	940.9		891.6
Employee compensation and benefits	276.7		395.6
Collaboration expense	298.3		277.9
Royalties and licensing fees	202.8		209.4


Other	712.7		746.9
Total accrued expense and other	$	3,838.4	$	2,521.4

Earnings per Share (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net income (loss) attributable to Biogen Inc.	$ (68.1)	$ 1,134.7	$ 911.4	$ 2,496.5
Weighted-average shares used in calculating:
Weighted average number of common shares outstanding	144,800	144,400	144,700	145,800
Effect of dilutive securities:
Dilutive potential common shares	0	400	800	400
Shares used in calculating diluted earnings per share	144,800	144,800	145,500	146,200
Time-vested restricted stock units
Effect of dilutive securities:
Stock units	0	300	700	300
Performance stock units settled in stock
Effect of dilutive securities:
Stock units	0	100	100	100

Collaborative and Other Relationships - Summary of Activity Related To Denali Therapeutics (Details) - Research and development - Denali Therapeutics - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 12.6	$ 19.9	$ 51.3	$ 58.0
Expense reflected within statements of income	$ 7.6	$ 11.4	$ 30.8	$ 33.5

Fair Value Measurements

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements


	Fair Value Measurements on a Recurring Basis
	As of September 30, 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	$	1,920.4	$	—	$	1,920.4	$	—




Marketable equity securities	413.6		413.6		—		—
Other current assets:
Receivable from Samsung BioLogics(1)	422.3		—		—		422.3
Derivative contracts	27.8		—		27.8		—
Other non-current assets:
Plan assets for deferred compensation	39.0		—		39.0		—
Derivative contracts	3.4		—		3.4		—
Total	$	2,826.5	$	413.6	$	1,990.6	$	422.3
Liabilities:
Derivative contracts	$	37.5	$	—	$	37.5	$	—

Total	$	37.5	$	—	$	37.5	$	—


	Fair Value Measurements on a Recurring Basis
	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 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	$	—

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 our consolidated financial statements included in our 2022 Form 10-K.

There have been no material impairments of our assets measured and carried at fair value as of September 30, 2023 and December 31, 2022. In addition, there have been no changes to our valuation techniques as of September 30, 2023 and December 31, 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 Note 1, Summary of Significant Accounting Policies - Fair Value Measurements, to our consolidated financial statements included in our 2022 Form 10-K.

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 September 30, 2023 and December 31, 2022.

Contingent Consideration Obligations


(In millions)	For the Three Months Ended September 30, 2022		For the Nine Months Ended September 30, 2022
Fair value, beginning of period	$	197.5	$	209.1
Changes in fair value	(2.1)		(13.7)

Fair value, end of period	$	195.4	$	195.4

Changes in the fair value of our contingent consideration obligations are recorded in (gain) loss on fair value remeasurement of contingent consideration in our condensed consolidated statements of income.

During the fourth quarter of 2022 we discontinued 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 fair value of vixotrigine to zero.

For the three and nine months ended September 30, 2022, the changes in fair value of our contingent consideration obligations were primarily due to increases in the discount rates used to revalue these obligations and delays in the expected timing of the achievement of certain remaining developmental milestones related to our vixotrigine programs.

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 condensed 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 and carrying values of our senior notes debt instruments, which are Level 2 liabilities, are summarized as follows:


	As of September 30, 2023				As of December 31, 2022
(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value

4.050% Senior Notes due September 15, 2025	$	1,689.6	$	1,746.2	$	1,699.9	$	1,744.7
2.250% Senior Notes due May 1, 2030	1,196.2		1,493.6		1,219.0		1,492.9
5.200% Senior Notes due September 15, 2045	972.7		1,100.5		1,033.2		1,100.3
3.150% Senior Notes due May 1, 2050	909.2		1,474.2		989.0		1,473.8
3.250% Senior Notes due February 15, 2051	430.8		471.9		469.1		469.3
Total	$	5,198.5	$	6,286.4	$	5,410.2	$	6,281.0

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 September 30, 2023, compared to December 31, 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 our consolidated financial statements included in our 2022 Form 10-K.

In connection with our acquisition of Reata we drew $1.0 billion on term loans under our term loan credit agreement. As of September 30, 2023, the fair value of our term loans outstanding approximate book value based on the current borrowing rates available. For additional information on our term loan credit agreement, please read Note 13, Indebtedness, to these condensed 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

Share-Based Payments (Details 1) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Share-Based Payments (Details 1) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	$ (64.8)	$ (65.7)	$ (217.8)	$ (194.1)
Subtotal	452.0	71.0	609.7	201.9
Capitalized share-based compensation costs	(2.6)	(2.0)	(8.5)	(7.1)
Share-based compensation expense included in total costs and expenses	449.4	69.0	601.2	194.8
Market stock units
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	0.7	4.0	4.2	11.4
Time-vested restricted stock units
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	53.4	48.7	175.0	150.4
Performance stock units settled in stock
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	7.8	10.5	27.1	22.1
Performance stock units settled in cash
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	0.1	5.4	4.8	7.9
Employee stock purchase plan
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	2.0	2.4	8.8	10.1
Options
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	1.0	0.0	2.8	0.0
Equity Awards Of Acquired Company
Summary of share based compensation expense associated with different programs [Abstract]
Share-based compensation expense	$ 387.0	$ 0.0	$ 387.0	$ 0.0

Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of financial assets with maturities of less than 90 days included within cash and cash equivalents

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 condensed consolidated balance sheets:


(In millions)	As of September 30, 2023		As of December 31, 2022
Commercial paper	$	—	$	177.2
Overnight reverse repurchase agreements	—		59.0
Money market funds	1,920.4		2,581.5

Short-term debt securities	—		29.9
Total	$	1,920.4	$	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 September 30, 2023
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value












Marketable equity securities

Marketable equity securities, non-current	$	993.3	$	—	$	(579.7)	$	413.6
Total marketable equity securities	$	993.3	$	—	$	(579.7)	$	413.6


	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 debt securities

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


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Proceeds from maturities and sales	$	5,698.6	$	1,643.2	$	7,380.8	$	3,104.7
Realized gains	1.0		—		1.4		—
Realized losses	16.3		7.9		18.4		9.3

- 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).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-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

Fair Value Measurements (Details 1) - USD ($) $ in Millions	9 Months Ended
Fair Value Measurements (Details 1) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Notes Payable	$ 6,286.4	$ 6,281.0
Debt Instrument, Fair Value Disclosure	5,198.5	5,410.2
BIIB054
Debt Instrument [Line Items]
Reduction in contingent consideration	195.4
4.050% Senior Notes due 2025
Debt Instrument [Line Items]
Notes payable, fair value	1,689.6	1,699.9
Notes Payable	1,746.2	1,744.7
2.250% Senior Notes due May 1, 2030
Debt Instrument [Line Items]
Notes payable, fair value	972.7	1,033.2
Notes Payable	1,100.5	1,100.3
5.200% Senior Notes due 2045
Debt Instrument [Line Items]
Notes payable, fair value	1,196.2	1,219.0
Notes Payable	1,493.6	1,492.9
3.250% Senior Notes, Due February 15, 2051
Debt Instrument [Line Items]
Notes payable, fair value	430.8	469.1
Notes Payable	471.9	469.3
3.150% Senior Notes due May 1, 2050
Debt Instrument [Line Items]
Notes payable, fair value	909.2	989.0
Notes Payable	$ 1,474.2	$ 1,473.8

Financial Instruments (Details 1) - USD ($) $ in Millions	Sep. 30, 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	$ 993.3	1,133.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(579.7)	(342.7)
Fair Value	413.6	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
Equity Securities, Current
Marketable equity securities
Amortized Cost		1,133.8
Gross Unrealized Gains		0.0
Gross Unrealized Losses		(342.7)
Fair Value		$ 791.1
Equity Securities, Non-Current
Marketable equity securities
Amortized Cost	993.3
Gross Unrealized Gains	0.0
Gross Unrealized Losses	(579.7)
Fair Value	$ 413.6

Revenues - Revenues by product (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Product revenues	$ 2,530.3	$ 2,508.5	$ 7,449.3	$ 7,629.4
MS Product Revenues
Disaggregation of Revenue [Line Items]
Product revenues	1,159.0	1,340.3	3,493.5	4,161.4
MS Product Revenues \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	631.8	707.9	1,814.6	2,170.7
MS Product Revenues \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	527.2	632.4	1,678.9	1,990.7
Fumarate
Disaggregation of Revenue [Line Items]
Product revenues	405.0	476.8	1,188.1	1,549.4
Fumarate \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	206.9	220.4	571.9	713.3
Fumarate \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	198.1	256.4	616.2	836.1
TECFIDERA
Disaggregation of Revenue [Line Items]
Product revenues	239.5	339.0	768.2	1,146.8
TECFIDERA \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	58.1	92.5	199.3	330.3
TECFIDERA \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	181.4	246.5	568.9	816.5
VUMERITY
Disaggregation of Revenue [Line Items]
Product revenues	165.5	137.8	419.9	402.6
VUMERITY \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	148.8	127.9	372.6	383.0
VUMERITY \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	16.7	9.9	47.3	19.6
Interferon
Disaggregation of Revenue [Line Items]
Product revenues	277.7	336.0	825.7	995.8
Interferon \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	180.1	214.5	492.6	608.0
Interferon \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	97.6	121.5	333.1	387.8
AVONEX
Disaggregation of Revenue [Line Items]
Product revenues	212.2	255.1	604.9	743.4
AVONEX \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	148.7	174.8	397.2	493.8
AVONEX \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	63.5	80.3	207.7	249.6
PLEGRIDY
Disaggregation of Revenue [Line Items]
Product revenues	65.5	80.9	220.8	252.4
PLEGRIDY \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	31.4	39.7	95.4	114.2
PLEGRIDY \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	34.1	41.2	125.4	138.2
TYSABRI
Disaggregation of Revenue [Line Items]
Product revenues	456.3	505.5	1,412.2	1,542.5
TYSABRI \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	244.8	273.0	750.1	849.4
TYSABRI \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	211.5	232.5	662.1	693.1
FAMPYRA
Disaggregation of Revenue [Line Items]
Product revenues	20.0	22.0	67.5	73.7
FAMPYRA \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	0.0	0.0	0.0	0.0
FAMPYRA \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	20.0	22.0	67.5	73.7
SPINRAZA
Disaggregation of Revenue [Line Items]
Product revenues	448.2	431.1	1,328.6	1,334.7
SPINRAZA \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	150.5	140.2	453.0	443.3
SPINRAZA \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	297.7	290.9	875.6	891.4
Biosimilars
Disaggregation of Revenue [Line Items]
Product revenues	194.3	187.6	581.8	576.3
Biosimilars \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	6.1	0.7	21.3	1.2
Biosimilars \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	188.2	186.9	560.5	575.1
BENEPALI
Disaggregation of Revenue [Line Items]
Product revenues	112.8	110.2	331.0	340.7
BENEPALI \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	0.0	0.0	0.0	0.0
BENEPALI \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	112.8	110.2	331.0	340.7
IMRALDI
Disaggregation of Revenue [Line Items]
Product revenues	54.4	57.7	167.6	172.4
IMRALDI \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	0.0	0.0	0.0	0.0
IMRALDI \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	54.4	57.7	167.6	172.4
FLIXABI
Disaggregation of Revenue [Line Items]
Product revenues	20.2	19.0	60.7	62.0
FLIXABI \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	0.0	0.0	0.0	0.0
FLIXABI \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	20.2	19.0	60.7	62.0
BYOOVIZ
Disaggregation of Revenue [Line Items]
Product revenues	6.9	0.7	22.5	1.2
BYOOVIZ \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	6.1	0.7	21.3	1.2
BYOOVIZ \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	0.8	0.0	1.2	0.0
Product, net
Disaggregation of Revenue [Line Items]
Product revenues	1,805.2	1,962.1	5,414.3	6,083.3
Product, net \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	790.9	850.4	2,293.3	2,619.7
Product, net \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	1,014.3	1,111.7	3,121.0	3,463.6
FUMADERM And ADUHELM
Disaggregation of Revenue [Line Items]
Product revenues	3.7	3.1	10.4	10.9
FUMADERM And ADUHELM \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	2.5	1.6	4.4	4.5
FUMADERM And ADUHELM \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	1.2	1.5	6.0	6.4
Spinal Muscular Atrophy
Disaggregation of Revenue [Line Items]
Product revenues	448.2	431.1	1,328.6	1,334.7
Spinal Muscular Atrophy \| U.S.
Disaggregation of Revenue [Line Items]
Product revenues	150.5	140.2	453.0	443.3
Spinal Muscular Atrophy \| Rest of World
Disaggregation of Revenue [Line Items]
Product revenues	$ 297.7	$ 290.9	$ 875.6	$ 891.4

Other Consolidated Financial Statement Detail (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Mar. 31, 2022
Other Income (Expense), Net
Gain on sale of equity interest in Samsung Bioepis(1)	$ 0.0	$ 0.0		$ 0.0	$ (1,505.4)
Litigation settlement agreement	0.0	0.0	$ 900.0	0.0	900.0
Interest income	(95.9)	(23.9)		(252.7)	(39.4)
Interest expense	63.8	59.9		175.4	191.8
(Gains) losses on investments, net	317.3	(101.8)		289.6	167.5
Foreign exchange (gains) losses, net	11.4	11.5		30.8	39.0
Other, net	3.4	(1.7)		5.1	25.2
Other (income) expense	300.0	(56.0)		248.2	(221.3)
Equity Securities, FV-NI, Gain (Loss), Alternative [Abstract]
Net (gains) losses recognized on equity securities	302.0	(109.8)		273.6	158.1
Less: Net (gains) losses realized on equity securities	4.4	(0.5)		5.3	0.0
Net unrealized (gains) losses recognized on equity securities	297.6	(109.3)		268.3	158.1
Accrued Expenses and Other
Reata acquisition-related accrued expense	1,407.0			1,407.0		$ 0.0
Revenue-related reserves for discounts and allowances	1,072.3			1,072.3		1,035.0
Collaboration expense	276.7			276.7		395.6
Royalties and licensing fees	202.8			202.8		209.4
Collaboration expense	298.3			298.3		277.9
Other	712.7			712.7		746.9
Total accrued expense and other	$ 3,838.4			$ 3,838.4		2,521.4
Samsung Bioepis
Other Income (Expense), Net
Equity, ownership interest	49.90%			49.90%			49.90%
Ionis, Sangamo, Denali and Sage
Equity Securities, FV-NI, Gain (Loss), Alternative [Abstract]
Net unrealized (gains) losses recognized on equity securities	$ 295.6	$ 112.5		$ 265.0	$ 198.0
Component of accrued expenses and other
Accrued Expenses and Other
Revenue-related reserves for discounts and allowances	$ 940.9			$ 940.9		$ 891.6