0000875045-23-000009 | 10-K | XBRL Viewer

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Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2022	Feb. 14, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	0-19311
Entity Registrant Name	BIOGEN INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0112644
Entity Address, Address Line One	225 Binney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	679-2000
Title of 12(b) Security	Common Stock, $0.0005 par value
Trading Symbol	BIIB
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 29,397,964,818
Entity Common Stock, Shares Outstanding		144,485,646
Documents Incorporated by Reference	Portions of the definitive proxy statement for our 2023 Annual Meeting of Stockholders are incorporated by reference into Part III of this report.
Entity Central Index Key	0000875045
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2022
Auditor Information [Abstract]
Auditor Firm ID	238
Auditor Location	Boston, Massachusetts
Auditor Name	PricewaterhouseCoopers LLP

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues	$ 10,173.4	$ 10,981.7	$ 13,444.6
Cost and expense:
Cost of sales, excluding amortization and impairment of acquired intangible assets	2,278.3	2,109.7	1,805.2
Research and development	2,231.1	2,501.2	3,990.9
Selling, general and administrative	2,403.6	2,674.3	2,504.5
Amortization and impairment of acquired intangible assets	365.9	881.3	464.8
Collaboration profit (loss) sharing	(7.4)	7.2	232.9
(Gain) loss on divestiture of Hillerød, Denmark manufacturing operations	0.0	0.0	(92.5)
(Gain) loss on fair value remeasurement of contingent consideration	(209.1)	(50.7)	(86.3)
Acquired in-process research and development	0.0	18.0	75.0
Restructuring charges	131.1	0.0	0.0
Gain on sale of building	(503.7)	0.0	0.0
Other (income) expense, net	(108.2)	1,095.5	(497.4)
Total cost and expense	6,581.6	9,236.5	8,397.1
Income before income tax expense and equity in loss of investee, net of tax	3,591.8	1,745.2	5,047.5
Income tax (benefit) expense	632.8	52.5	992.3
Equity in (income) loss of investee, net of tax	(2.6)	(34.9)	(5.3)
Net income	2,961.6	1,727.6	4,060.5
Net income (loss) attributable to noncontrolling interests, net of tax	(85.3)	171.5	59.9
Net income attributable to Biogen Inc.	$ 3,046.9	$ 1,556.1	$ 4,000.6
Net income per share:
Basic earnings per share attributable to Biogen Inc. (in dollars per share)	$ 20.96	$ 10.44	$ 24.86
Diluted earnings per share attributable to Biogen Inc. (in dollars per share)	$ 20.87	$ 10.40	$ 24.80
Weighted-average shares used in calculating:
Weighted average number of common shares outstanding (in shares)	145,300	149,100	160,900
Diluted earnings per share attributable to Biogen Inc. (in shares)	146,000	149,600	161,300
Product, net
Revenues	$ 7,987.8	$ 8,846.9	$ 10,692.2
Revenue from anti-CD20 therapeutic programs
Revenues	1,700.5	1,658.5	1,977.8
Other
Revenues	$ 485.1	$ 476.3	$ 774.6

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income attributable to Biogen Inc.	$ 3,046.9	$ 1,556.1	$ 4,000.6
Other comprehensive income:
Unrealized gains (losses) on securities available for sale, net of tax	(13.5)	(3.6)	(2.8)
Unrealized gains (losses) on cash flow hedges, net of tax	(38.7)	232.8	(186.8)
Gains (losses) on net investment hedges, net of tax	(25.5)	34.0	(33.6)
Unrealized gains (losses) on pension benefit obligation, net of tax	43.7	21.5	(33.5)
Currency translation adjustment	(24.2)	(92.4)	92.9
Total other comprehensive income (loss), net of tax	(58.2)	192.3	(163.8)
Comprehensive income (loss) attributable to Biogen Inc.	2,988.7	1,748.4	3,836.8
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	(85.3)	172.1	60.9
Comprehensive income (loss)	$ 2,903.4	$ 1,920.5	$ 3,897.7

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 3,419.3	$ 2,261.4
Marketable securities	1,473.5	1,541.1
Accounts receivable, net	1,705.0	1,549.4
Due from anti-CD20 therapeutic programs	431.4	412.3
Inventory	1,344.4	1,351.5
Other current assets	1,417.6	740.8
Total current assets	9,791.2	7,856.5
Marketable securities	705.7	892.0
Property, plant and equipment, net	3,298.6	3,416.4
Operating lease assets	403.9	375.4
Intangible assets, net	1,850.1	2,221.3
Goodwill	5,749.0	5,761.1
Deferred tax asset	1,226.4	1,415.1
Investments and other assets	1,529.2	1,939.5
Total assets	24,554.1	23,877.3
Current liabilities:
Current portion of notes payable	0.0	999.1
Taxes payable	259.9	174.7
Accounts payable	491.5	589.2
Accrued expense and other	2,521.4	2,535.2
Total current liabilities	3,272.8	4,298.2
Notes payable	6,281.0	6,274.0
Deferred tax liability	334.7	694.5
Long-term operating lease liabilities	333.0	330.4
Other long-term liabilities	944.2	1,320.5
Total liabilities	11,165.7	12,917.6
Commitments, contingencies and guarantees (Notes 22 and 23)
Biogen Inc. shareholders’ equity
Preferred stock, par value $0.001 per share	0.0	0.0
Common stock, par value $0.0005 per share	0.1	0.1
Additional paid-in capital	73.3	68.2
Accumulated other comprehensive loss	(164.9)	(106.7)
Retained earnings	16,466.5	13,911.7
Treasury stock, at cost; 23.8 million and 23.8 million shares, respectively	(2,977.1)	(2,977.1)
Total Biogen Inc. shareholders’ equity	13,397.9	10,896.2
Noncontrolling interests	(9.5)	63.5
Total equity	13,388.4	10,959.7
Total liabilities and equity	$ 24,554.1	$ 23,877.3

Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Millions	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, par value (in dollars per share)	$ 0.0005	$ 0.0005
Treasury stock at cost, shares (in shares)	23.8	23.8

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flow from operating activities:
Net income	$ 2,961.6	$ 1,727.6	$ 4,060.5
Adjustments to reconcile net income to net cash flow from operating activities:
Depreciation and amortization	518.4	487.7	457.2
Impairment of intangible assets	119.6	629.3	209.7
Excess and obsolescence charges related to inventory	336.2	167.6	26.6
Acquired in-process research and development	0.0	18.0	75.0
Share-based compensation	254.1	238.6	198.3
Contingent consideration	(209.1)	(50.7)	(86.3)
(Gain)/loss on divestiture of Hillerød, Denmark manufacturing operations	0.0	0.0	(92.5)
Deferred income taxes	(168.6)	(426.8)	149.0
(Gain) loss on strategic investments	265.9	826.8	(681.8)
(Gain) loss on equity method investment	(2.6)	(34.9)	(3.3)
Gain on sale of equity interest in Samsung Bioepis	(1,505.4)	0.0	0.0
Gain on sale of building	(503.7)	0.0	0.0
Other	208.2	202.2	104.6
Changes in operating assets and liabilities, net:
Accounts receivable	(203.4)	324.8	2.8
Due from anti-CD20 therapeutic programs	(19.0)	1.2	176.7
Inventory	(320.2)	(462.4)	(316.3)
Accrued expense and other current liabilities	(113.4)	(95.4)	154.2
Income tax assets and liabilities	(142.3)	230.8	(67.5)
Other changes in operating assets and liabilities, net	(92.0)	(144.5)	(137.1)
Net cash flow provided by (used in) operating activities	1,384.3	3,639.9	4,229.8
Cash flow from investing activities:
Purchases of property, plant and equipment	(240.3)	(258.1)	(424.8)
Proceeds from sales and maturities of marketable securities	3,671.0	3,405.4	7,299.4
Purchases of marketable securities	(3,448.5)	(3,808.7)	(6,397.7)
Proceeds from sale of equity interest in Samsung Bioepis	990.3	0.0	0.0
Proceeds from sale of building	582.6	0.0	0.0
Proceeds from divestiture of Hillerød, Denmark manufacturing operations	0.0	28.1	0.0
Acquired in-process research and development	0.0	(18.0)	(75.0)
Acquisitions of intangible assets	(2.9)	(18.8)	(52.0)
Proceeds from sales of strategic investments	0.0	93.5	74.9
Other	24.4	12.9	(26.9)
Net cash flow provided by (used in) investing activities	1,576.6	(563.7)	(608.6)
Cash flow from financing activities:
Purchase of treasury stock	(750.0)	(1,800.0)	(6,679.1)
Payments related to issuance of stock for share-based compensation arrangements, net	(1.9)	(0.7)	(4.6)
Repayments of borrowings and premiums paid on debt exchange	(1,002.2)	(170.0)	0.0
Proceeds from borrowings	0.0	0.0	2,967.4
Repayments of borrowings	0.0	0.0	(1,500.0)
Net (distribution) contribution to noncontrolling interest	12.4	(94.4)	(71.0)
Other	(5.6)	(21.1)	14.6
Net cash flow provided by (used in) financing activities	(1,747.3)	(2,086.2)	(5,272.7)
Net increase (decrease) in cash and cash equivalents	1,213.6	990.0	(1,651.5)
Effect of exchange rate changes on cash and cash equivalents	(55.7)	(59.8)	69.0
Cash and cash equivalents, beginning of the year	2,261.4	1,331.2	2,913.7
Cash and cash equivalents, end of the year	3,419.3	2,261.4	1,331.2
Sangamo Therapeutics, Inc. Agreement
Cash flow from investing activities:
Purchase of subsidiaries and affiliates	0.0	0.0	(141.8)
Denali Therapeutics
Cash flow from investing activities:
Purchase of subsidiaries and affiliates	0.0	0.0	(423.7)
Sage Therapeutics
Cash flow from investing activities:
Purchase of subsidiaries and affiliates	$ 0.0	$ 0.0	$ (441.0)

Consolidated Statements of Equity - USD ($) shares in Millions, $ in Millions	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Retained earnings	Treasury stock	Total Biogen Inc. shareholders’ equity	Noncontrolling interests	2020 Share Repurchase Program	2020 Share Repurchase Program Common stock	2020 Share Repurchase Program Additional paid-in capital	2020 Share Repurchase Program Retained earnings	2020 Share Repurchase Program Treasury stock	2020 Share Repurchase Program Total Biogen Inc. shareholders’ equity	December 2019 Share Repurchase Program	December 2019 Share Repurchase Program Common stock	December 2019 Share Repurchase Program Additional paid-in capital	December 2019 Share Repurchase Program Retained earnings	December 2019 Share Repurchase Program Treasury stock	December 2019 Share Repurchase Program Total Biogen Inc. shareholders’ equity	March 2019 Share Repurchase Program	March 2019 Share Repurchase Program Common stock	March 2019 Share Repurchase Program Additional paid-in capital	March 2019 Share Repurchase Program Retained earnings	March 2019 Share Repurchase Program Treasury stock	March 2019 Share Repurchase Program Total Biogen Inc. shareholders’ equity
Beginning balance (in shares) at Dec. 31, 2019		198.0				23.8
Beginning balance at Dec. 31, 2019	$ 13,339.1	$ 0.1	$ 0.0	$ (135.2)	$ 16,455.4	$ (2,977.1)	$ 13,343.2	$ (4.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,060.5				4,000.6		4,000.6	59.9
Other comprehensive income (loss), net of tax	(162.8)			(163.8)			(163.8)	1.0
Distribution to noncontrolling interest	(75.0)						0.0	(75.0)
Capital contribution from noncontrolling interest	4.0							4.0
Repurchase of common stock pursuant to the share repurchase program, at cost (in shares)									(1.6)				(1.6)		(16.7)				(16.7)		(4.1)				(4.1)
Repurchase of common stock pursuant to the share repurchase program, at cost									$ (400.0)				$ (400.0)	$ (400.0)	$ (5,000.0)				$ (5,000.0)	$ (5,000.0)	$ (1,279.1)				$ (1,279.1)	$ (1,279.1)
Retirement of common stock pursuant to the share repurchase program, at cost (in shares)										1.6			1.6			16.7			16.7			4.1			4.1
Retirement of common stock pursuant to the share repurchase program, at cost									$ 0.0		$ (60.8)	$ (339.2)	$ 400.0		$ 0.0		$ (121.3)	$ (4,878.7)	$ 5,000.0		$ 0.0		$ (71.0)	$ (1,208.1)	$ 1,279.1
Issuance of common stock under stock option and stock purchase plans (in shares)		0.2
Issuance of common stock under stock option and stock purchase plans	49.3		49.3				49.3
Issuance of common stock under stock award plan (in shares)		0.4
Issuance of common stock under stock award plan	(53.7)				(53.7)		(53.7)
Compensation expense related to share-based payments	204.5		204.5				204.5
Other	(0.7)		(0.7)				(0.7)
Ending balance (in shares) at Dec. 31, 2020		176.2				23.8
Ending balance at Dec. 31, 2020	10,686.1	$ 0.1	0.0	(299.0)	13,976.3	$ (2,977.1)	10,700.3	(14.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,727.6				1,556.1		1,556.1	171.5
Other comprehensive income (loss), net of tax	192.9			192.3			192.3	0.6
Distribution to noncontrolling interest	(100.0)							(100.0)
Capital contribution from noncontrolling interest	5.6							5.6
Repurchase of common stock pursuant to the share repurchase program, at cost (in shares)									(6.0)				(6.0)
Repurchase of common stock pursuant to the share repurchase program, at cost									$ (1,800.0)				$ (1,800.0)	(1,800.0)
Retirement of common stock pursuant to the share repurchase program, at cost (in shares)										6.0			6.0
Retirement of common stock pursuant to the share repurchase program, at cost									$ 0.0		(231.9)	(1,568.1)	$ 1,800.0
Issuance of common stock under stock option and stock purchase plans (in shares)		0.2
Issuance of common stock under stock option and stock purchase plans	54.4		54.4				54.4
Issuance of common stock under stock award plan (in shares)		0.4
Issuance of common stock under stock award plan	(55.0)		(2.4)		(52.6)		(55.0)
Compensation expense related to share-based payments	246.6		246.6				246.6
Other	1.5		1.5				1.5
Ending balance (in shares) at Dec. 31, 2021		170.8				23.8
Ending balance at Dec. 31, 2021	10,959.7	$ 0.1	68.2	(106.7)	13,911.7	$ (2,977.1)	10,896.2	63.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,961.6				3,046.9		3,046.9	(85.3)
Other comprehensive income (loss), net of tax	(58.2)			(58.2)			(58.2)	0.0
Distribution to noncontrolling interest	0.0							0.0
Capital contribution from noncontrolling interest	12.3							12.3
Repurchase of common stock pursuant to the share repurchase program, at cost (in shares)									(3.6)				(3.6)
Repurchase of common stock pursuant to the share repurchase program, at cost									$ (750.0)				$ (750.0)	$ (750.0)
Retirement of common stock pursuant to the share repurchase program, at cost (in shares)										3.6			3.6
Retirement of common stock pursuant to the share repurchase program, at cost									$ 0.0		$ (257.9)	$ (492.1)	$ 750.0
Issuance of common stock under stock option and stock purchase plans (in shares)		0.2
Issuance of common stock under stock option and stock purchase plans	44.2		44.2		0.0		44.2
Issuance of common stock under stock award plan (in shares)		0.5
Issuance of common stock under stock award plan	(46.0)		(46.0)		0.0		(46.0)
Compensation expense related to share-based payments	263.5		263.5				263.5
Other	1.3		1.3				1.3
Ending balance (in shares) at Dec. 31, 2022		167.9				23.8
Ending balance at Dec. 31, 2022	$ 13,388.4	$ 0.1	$ 73.3	$ (164.9)	$ 16,466.5	$ (2,977.1)	$ 13,397.9	$ (9.5)

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Summary of Significant Accounting Policies


Note 1:			Summary of Significant Accounting Policies

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

Business Overview

Biogen is a global biopharmaceutical company focused on discovering, developing and delivering innovative therapies for people living with serious and complex diseases worldwide. We have a broad portfolio of medicines to treat multiple sclerosis (MS), have introduced the first approved treatment for spinal muscular atrophy (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; ADUHELM for the treatment of Alzheimer's disease; and FUMADERM for the treatment of severe plaque psoriasis. We also collaborate with Eisai Co., Ltd. (Eisai) on the commercialization of LEQEMBI for the treatment of Alzheimer's disease, which was granted accelerated approval by the U.S. Food and Drug Administration (FDA) in January 2023. We have certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, chronic lymphocytic leukemia (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 primary progressive MS (PPMS) and relapsing MS (RMS); LUNSUMIO (mosunetuzumab), which was granted accelerated approval in the U.S. during the fourth quarter of 2022 for the treatment of relapsed or refractory follicular lymphoma; glofitamab, an investigational bispecific antibody for the potential treatment of non-Hodgkin's lymphoma; and have the option to add other potential anti-CD20 therapies, pursuant to our collaboration arrangements with Genentech, Inc. (Genentech), a wholly-owned member of the Roche Group.

In addition to continuing to invest in new potential innovation in MS and SMA we are advancing our mid-to-late stage programs including zuranolone for major depressive disorder (MDD) and postpartum depression (PPD), BIIB080 for Alzheimer's disease, tofersen for amyotrophic lateral sclerosis (ALS) and both litifilimab and dapirolizumab pegol for certain forms of lupus.

We also 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, in the U.S. We continue to develop potential biosimilar products including BIIB800, a proposed tocilizumab biosimilar referencing ACTEMRA, and SB15, a proposed aflibercept biosimilar referencing EYLEA.

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

Consolidation

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

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

Use of Estimates

The preparation of our consolidated financial statements requires us to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, equity, revenue and expense and related disclosure of contingent assets and liabilities. On an ongoing basis we evaluate our estimates, judgments and assumptions. We base our estimates on historical experience and on various other assumptions that we believe are reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenue and expense. Actual results may differ from these estimates.

The length of time and full extent to which the COVID-19 pandemic directly or indirectly impacts our business, results of operations and financial condition, including sales, expense, reserves and allowances, the supply chain, manufacturing, clinical trials, research and development costs and employee-related costs, depends on future developments that are highly uncertain, subject to change and are difficult to predict, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19 as well as the economic impact on local, regional, national and international customers and markets. Additionally, the ongoing geopolitical tensions related to the conflict in Ukraine, and the related sanctions and other penalties imposed, are creating substantial uncertainty in the global economy. The extent and duration of the conflict, sanctions and resulting market disruptions are highly unpredictable. We have made estimates of the impact of the COVID-19 pandemic and the ongoing geopolitical conflict in Ukraine within our consolidated financial statements and there may be changes to those estimates in future periods.

Revenue Recognition

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

Product Revenue

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

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

Reserves for Discounts and Allowances

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

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

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

estimates. If actual results vary, we adjust these estimates, which could have an effect on earnings in the period of adjustment.

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

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

•Medicaid rebates: relate to our estimated obligations to states under established reimbursement arrangements. Rebate accruals are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expense and other current liabilities in our consolidated balance sheets. Our liability for Medicaid rebates consists of estimates for claims that a state will make for the current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, invoices received for claims from the prior quarters that have not been paid and an estimate of potential claims that will be made for inventory that exists in the distribution channel at period end.

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

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

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

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

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

Product return reserves are established for returns made by wholesalers and are recorded in the period the related revenue is recognized, resulting in a reduction to product revenue. In accordance with contractual terms, wholesalers are permitted to return product for reasons such as damaged or expired product. The majority of

wholesaler returns are due to product expiration. Expired product return reserves are estimated through a comparison of historical return data to their related sales on a production lot basis. Historical rates of return are determined for each product and are adjusted for known or expected changes in the marketplace specific to each product.

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

Revenue from Anti-CD20 Therapeutic Programs

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

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

Revenue from anti-CD20 therapeutic programs consist of:

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

(ii) royalty revenue on sales of OCREVUS; and

(ii) other revenue from anti-CD20 therapeutic programs, which consists of our share of pre-tax co-promotion profits on RITUXAN in Canada.

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

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

In January 2022 we exercised our option with Genentech to participate in the joint development and commercialization of LUNSUMIO, which was later approved by the FDA in December 2022. Under our collaboration with Genentech, we will be entitled to co-promotion operating profits and losses in the U.S. for LUNSUMIO.

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

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

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

Other Revenue

Contract Manufacturing and Other Revenue

We record contract manufacturing and other revenue primarily from amounts earned under contract manufacturing agreements. Revenue under contract manufacturing agreements is recognized when the customer obtains control of the product, which may occur at a point in time or over time depending on the terms and conditions of the agreement.

Royalty Revenue

Royalty revenue reflects the royalties we receive from net sales on products related to patents that we have out-licensed, as well as royalty revenue on biosimilar products from our collaboration arrangements with Samsung Bioepis Co., Ltd. (Samsung Bioepis). These arrangements resulted from an exchange of a license and utilize the sales and usage based royalty exception. Therefore, royalties received are recognized as the underlying sales occur.

Collaborative and Other Relationships

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

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

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

Fair Value Measurements

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

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

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

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

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

We validate the prices provided by our third-party pricing services by understanding the models used, obtaining market values from other pricing sources and analyzing pricing data in certain instances. The option pricing valuation models use assumptions within the model, including the term, stock price volatility, constant maturity risk-free interest rate and dividend yield. After completing our validation procedures, we did not adjust or override any fair value measurements provided by our pricing services as of December 31, 2022 and 2021.

Other Assets and Liabilities

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

Cash and Cash Equivalents

We consider only those investments that are highly liquid, readily convertible to cash and that mature within three months from date of purchase to be cash equivalents. As of December 31, 2022 and 2021, cash equivalents were comprised of money market funds, commercial paper, overnight reverse repurchase agreements and other debt securities with maturities less than three months from the date of purchase.

Accounts Receivable

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

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

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

Receivables from Samsung BioLogics

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

Concentration of Credit Risk

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

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

Marketable Securities and Other Investments

Marketable Debt Securities

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

Marketable Equity Securities and Venture Capital Funds

Our marketable equity securities are recorded at fair market value and unrealized gains and losses are included in other (income) expense, net in our consolidated statements of income. Our marketable equity securities represent investments in publicly traded equity securities and are included in investments and other assets in our consolidated balance sheets.

Our investments in venture capital funds are recorded at net asset value, which approximates fair value, and unrealized gains and losses are included in other (income) expense, net in our consolidated statements of income. The underlying investments of the venture capital funds in which we invest are in equity securities of certain biotechnology companies and are included in investments and other assets in our consolidated balance sheets.

Non-Marketable Equity Securities

We also invest in equity securities of companies whose securities are not publicly traded and where fair value is not readily available. These investments are recorded using either the equity method of accounting or the cost minus impairment adjusted for observable price changes, depending on our ownership percentage and other factors that suggest we have significant influence. We monitor these investments to evaluate whether any increase or decline in their value has occurred, based on the implied value of recent company financings, public market prices of comparable companies and general market conditions. These investments are included in investments and other assets in our consolidated balance sheets.

Evaluating Marketable Debt Securities for Other-than-Temporary Impairments

We conduct periodic reviews to identify and evaluate each investment that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. Unrealized losses on available-for-sale debt securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, in accumulated other comprehensive income (loss).

For available-for-sale debt securities with unrealized losses, management performs an analysis to assess whether we intend to sell or whether we would more likely than not be required to sell the security before the expected recovery of the amortized cost basis. Where we intend to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is reflected in earnings as an impairment loss.

Regardless of our intent to sell a security, we perform additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security.

Equity Method of Accounting

In circumstances where we have the ability to exercise significant influence over the operating and financial policies of a company in which we have an investment, we utilize the equity method of accounting for recording investment activity. In assessing whether we exercise significant influence, we consider the nature and magnitude of our investment, the voting and protective rights we hold, any participation in the governance of the other company and other relevant factors such as the presence of a collaborative or other business relationship. Under the equity method of accounting, we record in our consolidated statements of income our share of income or loss of the other company. If our share of losses exceeds the carrying value of our investment, we will suspend recognizing additional losses and will continue to do so unless we commit to providing additional funding.

Inventory

Inventories are stated at the lower of cost or net realizable value with cost based on the first-in, first-out method. We classify our inventory costs as long-term when we expect to utilize the inventory beyond our normal operating cycle and include these costs in investments and other assets in our consolidated balance sheets. Inventory that can be used in either the production of clinical or commercial products is expensed as research and development costs when identified for use in a clinical manufacturing campaign.

Capitalization of Inventory Costs

We capitalize inventory costs associated with our products prior to regulatory approval, when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is

expected to be realized. We consider numerous attributes in evaluating whether the costs to manufacture a particular product should be capitalized as an asset. We assess the regulatory approval process and where the particular product stands in relation to that approval process, including any known safety or efficacy concerns, potential labeling restrictions and other impediments to approval. We evaluate our anticipated research and development initiatives and constraints relating to the product and the indication in which it will be used. We consider our manufacturing environment including our supply chain in determining logistical constraints that could hamper approval or commercialization. We consider the shelf life of the product in relation to the expected timeline for approval and we consider patent related or contract issues that may prevent or delay commercialization. We also base our judgment on the viability of commercialization, trends in the marketplace and market acceptance criteria. Finally, we consider the reimbursement strategies that may prevail with respect to the product and assess the economic benefit that we are likely to realize. We expense previously capitalized costs related to pre-approval inventory upon changes in such judgments, due to, among other potential factors, a denial or significant delay of approval by necessary regulatory bodies.

Obsolescence and Unmarketable Inventory

At each reporting period we review our inventories for excess or obsolescence and write-down obsolete or otherwise unmarketable inventory to its estimated net realizable value. If the actual net realizable value is less than that estimated by us, or if it is determined that inventory utilization will further diminish based on estimates of demand, additional inventory write-downs may be required. Additionally, our products are subject to strict quality control and monitoring that we perform throughout the manufacturing process. In the event that certain batches or units of product no longer meet quality specifications, we will record a charge to cost of sales to write-down any unmarketable inventory to its estimated net realizable value. In all cases, product inventory is carried at the lower of cost or its estimated net realizable value. Amounts written-down due to unmarketable inventory are charged to cost of sales in our consolidated statements of income.

Property, Plant and Equipment

Property, plant and equipment are carried at cost, subject to reviews for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The cost of normal, recurring or periodic repairs and maintenance activities related to property, plant and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits.

Interest costs incurred during the construction of major capital projects are capitalized until the underlying asset is ready for its intended use, at which point the interest costs are amortized as depreciation expense over the life of the underlying asset. We also capitalize certain direct and incremental costs associated with the validation effort required for licensing by regulatory agencies of new manufacturing equipment for the production of a commercially approved drug. These costs primarily include direct labor and material and are incurred in preparing the equipment for its intended use. The validation costs are either amortized over the life of the related equipment or expensed as cost of sales when the product produced in the validation process is sold.

In addition, we capitalize certain internal use computer software development costs. If the software is an integral part of production assets, these costs are included in machinery and equipment and are amortized on a straight-line basis over the estimated useful lives of the related software, which generally range from three to five years.

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


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

When we dispose of property, plant and equipment, we remove the associated cost and accumulated depreciation from the related accounts in our consolidated balance sheets and include any resulting gain or loss in our consolidated statements of income.

Leases

We determine if an arrangement is a lease at contract inception. Operating lease assets represent our right to use an underlying asset for the lease term and operating lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, we include options to extend or terminate the lease when it is reasonably certain that they will be exercised.

We use the implicit rate when readily determinable and use our incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. Our incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease.

The lease payments used to determine our operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized in our operating lease assets in our consolidated balance sheets. Our lease agreements may include both lease and non-lease components, which we account for as a single lease component when the payments are fixed. Variable payments included in the lease agreement are expensed as incurred. For certain equipment leases, such as vehicles, we apply a portfolio approach to effectively account for the operating lease assets and liabilities.

Our operating leases are reflected in operating lease assets, accrued expense and other and in long-term operating lease liabilities in our consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

We also have real estate lease agreements which are subleased to third-parties. Operating leases for which we are the sublessor are included in accrued expense and other and other long-term liabilities in our consolidated balance sheets. We recognize sublease income on a straight-line basis over the lease term in our consolidated statements of income.

For additional information on our leases, please read Note 12, Leases, to these consolidated financial statements.

Intangible Assets

Our intangible assets consist of completed technology (comprised of acquired and in-licensed rights and patents, developed technology, out-licensed patents), in-process research and development (IPR&D) acquired after January 1, 2009, trademarks and trade names. Our intangible assets are recorded at fair value at the time of their acquisition and are stated in our consolidated balance sheets net of accumulated amortization and impairments, if applicable.

Intangible assets related to acquired and in-licensed rights and patents, developed technology and out-licensed patents are amortized over their estimated useful lives using the economic consumption method if anticipated future revenue can be reasonably estimated. The straight-line method is used when revenue cannot be reasonably estimated. Amortization is recorded within amortization and impairment of acquired intangible assets in our consolidated statements of income.

We amortize the intangible assets related to our marketed products using the economic consumption method based on revenue generated from the products underlying the related intangible assets. An analysis of the anticipated lifetime revenue of our marketed products is performed annually during our long-range planning cycle and whenever events or changes in circumstances would significantly affect anticipated lifetime revenue of the relevant products.

Intangible assets related to trademarks, trade names and IPR&D prior to commercialization are not amortized because they have indefinite lives; however, they are subject to review for impairment. We review our intangible assets with indefinite lives for impairment annually, as of October 31, and whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable.

Acquired In-process Research and Development (IPR&D)

Acquired IPR&D represents the fair value assigned to research and development assets that have not reached technological feasibility. The value assigned to acquired IPR&D is determined by estimating the costs to develop the acquired technology into commercially viable products, estimating the resulting revenue from the projects and discounting the net cash flow to present value. The revenue and cost projections used to value acquired IPR&D are, as applicable, reduced based on the probability of success of developing a new drug. Additionally, the projections consider the relevant market sizes and growth factors, expected trends in technology and the nature and expected timing of new product introductions by us and our competitors. The rates utilized to discount the net cash flow to present value are commensurate with the stage of development of the projects and uncertainties in the economic estimates used in the projections. Upon the acquisition of IPR&D, we complete an assessment of whether our acquisition constitutes the purchase of a single asset or a group of assets. We consider multiple factors in this assessment, including the nature of the technology acquired, the presence or absence of separate cash flow, the development process and stage of completion, quantitative significance and our rationale for entering into the transaction.

If we acquire a business as defined under applicable accounting standards, then the acquired IPR&D is capitalized as an intangible asset. If we acquire an asset or group of assets that do not meet the definition of a business under applicable accounting standards, then the acquired IPR&D is expensed on its acquisition date. Future costs to develop these assets are recorded to research and development expense in our consolidated statements of income as they are incurred.

When performing our impairment assessment, we calculate the fair value using the same methodology as described above. If the carrying value of our acquired IPR&D exceeds its fair value, then the intangible asset is written down to its fair value. Changes in estimates and assumptions used in determining the fair value of our acquired IPR&D could result in an impairment. Impairments are recorded within amortization and impairment of acquired intangible assets in our consolidated statements of income.

Goodwill

Goodwill represents the difference between the purchase price and the fair value of the identifiable tangible and intangible net assets when accounted for using the purchase method of accounting. Goodwill is not amortized, but is reviewed for impairment annually, as of October 31, and whenever events or changes in circumstances indicate that the carrying value of the goodwill may not be recoverable.

We compare the fair value of our reporting unit to its carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of our reporting unit, we would record an impairment loss equal to the difference. As described in Note 25, Segment Information, to these consolidated financial statements, we operate as one operating segment, which is our only reporting unit.

Impairment of Long-Lived Assets

Long-lived assets to be held and used, including property, plant and equipment, and definite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets or asset group may not be recoverable.

Determination of recoverability is based on an estimate of undiscounted future cash flow resulting from the use of the asset and its eventual disposition. In the event that such cash flow is not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their fair values. Long-lived assets to be disposed of are carried at fair value less costs to sell.

Contingent Consideration

The consideration for our acquisitions often includes future payments that are contingent upon the occurrence of a particular event or events. We record an obligation for such contingent payments at fair value on the acquisition date. We estimate the fair value of contingent consideration obligations through valuation models that incorporate probability-adjusted assumptions related to the achievement of the milestones and thus likelihood of making related payments. We revalue our contingent consideration obligations each reporting period. Changes in the fair value of our contingent consideration obligations are recognized in our consolidated statements of income. Changes in the fair value of the contingent consideration obligations can result from changes to one or multiple inputs, including adjustments to the discount rates, changes in the amount or timing of expected expenditures associated with product development, changes in the amount or timing of cash flow and reserves associated with products upon

Discount rates in our valuation models represent a measure of the credit risk associated with settling the liability. The period over which we discount our contingent obligations is based on the current development stage of the product candidates, our specific development plan for that product candidate adjusted for the probability of completing the development step and when the contingent payments would be triggered. In estimating the probability of success, we utilize data regarding similar milestone events from several sources, including industry studies and our own experience. These fair value measurements are based on significant inputs not observable in the market. Significant judgment is employed in determining the appropriateness of these assumptions as of the acquisition date and for each subsequent period.

Derivative Instruments and Hedging Activities

Cash Flow and Fair Value Derivative Instruments

We recognize all derivative instruments as either assets or liabilities at fair value in our consolidated balance sheets. Changes in the fair value of our derivative instruments are recognized each period in current earnings or accumulated other comprehensive income (loss), depending on whether the derivative instrument is designated as part of a hedge transaction and, if so, the type of hedge transaction. We classify the cash flow from these instruments in the same category as the cash flow from the hedged items. We do not hold or issue derivative instruments for trading or speculative purposes.

We assess at inception and on an ongoing basis, whether the derivative instruments that are used in hedging transactions are highly effective in offsetting the changes in cash flow or fair values of the hedged items. We exclude the forward points portion of the derivative instruments used in a hedging transaction from the effectiveness test and record the fair value gain or loss related to this portion each period in our consolidated statements of income in the same line as the underlying hedged item. If we determine that a forecasted transaction is no longer probable of occurring, we discontinue hedge accounting for the affected portion of the hedge instrument, and any related unrealized gain or loss on the contract is recognized in current earnings.

Net Investment Derivative Instruments

Designated net investment hedges are recognized as either assets or liabilities, at fair value, in our consolidated balance sheets. We hedge the changes in the spot exchange rate in accumulated other comprehensive income (loss) and exclude changes to the forward rate and amortize the forward points in other (income) expense, net in our consolidated statements of income over the term of the contract. We classify the cash flow from these instruments in the same category as the cash flow from the hedged items.

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

For additional information on our derivative instruments and hedging activities, please read Note 10, Derivative Instruments, to these consolidated financial statements.

Translation of Foreign Currencies

The functional currency for most of our foreign subsidiaries is their local currency. For our non-U.S. subsidiaries that transact in a functional currency other than the U.S. dollar, assets and liabilities are translated at current rates of exchange at the balance sheet date. Income and expense items are translated at the average foreign currency exchange rates for the period. Adjustments resulting from the translation of the financial statements of our foreign operations into U.S. dollars are excluded from the determination of net income and are recorded in accumulated other comprehensive income (loss), as a separate component of equity. For subsidiaries where the functional currency of the assets and liabilities differ from the local currency, non-monetary assets and liabilities are translated at the rate of exchange in effect on the date assets were acquired while monetary assets and liabilities are translated at current rates of exchange as of the balance sheet date. Income and expense items are translated at the average foreign currency rates for the period. Translation adjustments of these subsidiaries are included in other (income) expense, net in our consolidated statements of income.

Royalty Cost of Sales

We make royalty payments to a number of third-parties under license or purchase agreements associated with our acquisition of intellectual property. These royalty payments are typically calculated as a percentage (royalty rate) of the sales of our products in a particular year. That royalty rate may remain constant, increase or decrease within each year based on the total amount of sales during the annual period. Each quarterly period, we estimate our total royalty obligation for the full year and recognize the proportional amount as cost of sales based on actual quarterly sales as a percentage of full year estimated sales. For example, if the level of net sales in any calendar year increases the royalty rate within the year, we will record our cost of sales at an even rate over the year, based on the estimated blended royalty rate.

Accounting for Share-Based Compensation

Our share-based compensation programs grant awards that have included stock options, restricted stock units that vest based on stock performance known as market stock units (MSUs), performance-vested restricted stock units that settle in cash (CSPUs), time-vested restricted stock units (RSUs), performance-vested restricted stock units that can be settled in cash or shares of our common stock (PUs) at the sole discretion of the Compensation and Management Development Committee of our Board of Directors, performance-vested stock units that settle in stock or cash (PSUs) and shares issued under our employee stock purchase plan (ESPP). Compensation expense is recognized based on the estimated fair value of the awards at grant date. We recognize compensation expense for the number of awards expected to vest after taking into consideration an estimate of award forfeitures over the requisite service period, which is generally the vesting period. Where awards are made with non-substantive vesting periods (for instance, where a portion of the award vests upon retirement eligibility), we estimate and recognize expense based on the period from the grant date to the date the employee becomes retirement eligible.

The fair values of our stock option grants are estimated as of the date of grant using a Black-Scholes option valuation model. The estimated fair values of the stock options are then expensed over the options' vesting periods.

The fair values of our MSUs are estimated using a lattice model with a Monte Carlo simulation. We apply an accelerated attribution method to recognize share-based compensation expense over the applicable service period for our MSUs. The probability of actual shares expected to be earned is considered in the grant date valuation, therefore the expense is not adjusted to reflect the actual units earned.

The fair values of our RSUs are based on the market value of our stock on the date of grant. Compensation expense for RSUs is recognized straight-line over the applicable service period.

We apply an accelerated attribution method to recognize share-based compensation expense when accounting for our CSPUs, PUs and PSUs that settle in cash, and the fair value of the liability is remeasured at the end of each reporting period through expected settlement. Compensation expense associated with CSPUs, PUs and PSUs that settle in cash are based upon the stock price and the number of units expected to be earned after assessing the probability that certain performance criteria will be met and the targeted payout level associated with the performance criteria expected to be achieved. Cumulative adjustments are recorded each quarter to reflect changes in the stock price and estimated outcome of the performance-related conditions until the date results are determined and settled. If performance criteria are not met or not expected to be met, any compensation expense previously recognized to date associated with the awards will be reversed.

The fair values of PSUs that settle in stock are based upon the stock price on the date of grant. Compensation expense is recognized for the number of units expected to be earned after assessing the probability that certain performance criteria will be met and the targeted payout level associated with the performance criteria expected to be achieved. Cumulative adjustments are recorded each quarter to reflect the estimated outcome of the performance-related conditions until the date results are determined and settled. If performance criteria are not met or not expected to be met, any compensation expense previously recognized to date associated with the awards will be reversed.

Research and Development Expense

Research and development expense consists of expenses incurred in performing research and development activities, which include compensation and benefits, facilities and overhead expense, clinical trial expense and fees paid to contract research organizations (CROs), clinical supply and manufacturing expense, write-offs of inventory that was previously capitalized in anticipation of product launch and determined to no longer be realizable and other outside expense and upfront fees and milestones paid to third-party collaborators. Research and development

expense is expensed as incurred. Upfront and milestone payments made to third-party collaborators are expensed as incurred up to the point of regulatory approval. Milestone payments made upon regulatory approval are capitalized and amortized over the remaining useful life of the related product. Payments we make for research and development services prior to the services being rendered are recorded as prepaid assets in our consolidated balance sheets and are expensed as the services are provided. We also accrue the costs of ongoing clinical trials associated with programs that have been terminated or discontinued for which there is no future economic benefit at the time the decision is made to terminate or discontinue the program.

From time to time, we enter into development agreements in which we share expenses with a collaborative partner. We record payments received from our collaborative partners for their share of the development costs as a reduction of research and development expense, except as discussed in Note 19, Collaborative and Other Relationships, to these consolidated financial statements. Expenses incurred by Genentech in the ongoing development of RITUXAN, GAZYVA and other products for which an initial indication has been approved are not recorded as research and development expense, but rather reduce our share of profits recorded as a component of revenue from anti-CD20 therapeutic programs.

For collaborations with commercialized products, if we are the principal, we record revenue and the corresponding operating costs in their respective line items in our consolidated statements of income. If we are not the principal, we record operating costs as a reduction of revenue.

Selling, General and Administrative Expense

Selling, general and administrative expense is primarily comprised of compensation and benefits associated with sales and marketing, finance, human resources, legal, information technology and other administrative personnel, outside marketing, advertising and legal expense and other general and administrative costs.

Advertising costs are expensed as incurred. For the years ended December 31, 2022, 2021 and 2020, advertising costs totaled $54.1 million, $98.7 million and $111.8 million, respectively.

Income Taxes

The provision for income taxes includes federal, state, local and foreign taxes. Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be recovered or settled. We evaluate the realizability of our deferred tax assets and establish a valuation allowance when it is more likely than not that all or a portion of deferred tax assets will not be realized. We recognize deferred taxes associated with our global intangible low-taxed income (GILTI) tax calculations.

The income tax consequences from the intra-entity transfers of inventory within our consolidated group, both current and deferred, are recorded as a prepaid tax or deferred charge and recognized through our consolidated statements of income when the inventory is sold to a third-party. The income tax consequences from the intra-entity transfer of assets other than inventory and associated changes to deferred taxes are recognized when the transfer occurs.

We account for uncertain tax positions using a “more likely than not” threshold for recognizing and resolving uncertain tax positions. We evaluate uncertain tax positions on a quarterly basis and consider various factors including, but not limited to, changes in tax law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, information obtained during in process audit activities and changes in facts or circumstances related to a tax position. We also accrue for potential interest and penalties related to unrecognized tax benefits in income tax (benefit) expense in our consolidated statements of income.

Contingencies

We are currently involved in various claims and legal proceedings. Loss contingency provisions are recorded if the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount can be reasonably estimated or a range of loss can be determined. These accruals represent management’s best estimate of probable loss. Disclosure also is provided when it is reasonably possible that a loss will be incurred or when it is reasonably possible that the amount of a loss will exceed the recorded provision. On a quarterly basis, we review the status of each significant matter and assess its potential financial exposure. Significant judgment is

required in both the determination of probability and as to whether an exposure is reasonably estimable. Because of uncertainties related to these matters, accruals are based only on the best information available at the time. As additional information becomes available, we reassess the potential liability related to pending claims and litigation and may change our estimates. Legal costs associated with legal proceedings are expensed when incurred.

Earnings per Share

Basic earnings per share is computed by dividing undistributed net income attributable to Biogen Inc. by the weighted-average number of common shares outstanding during the period. Diluted earnings per share is computed based on the treasury method by dividing net income by the weighted-average number of common shares outstanding during the period plus potentially dilutive common equivalent shares outstanding.

New Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that we adopt as of the specified effective date. Unless otherwise discussed below, we do not believe that the adoption of recently issued standards have or may have a material impact on our consolidated financial statements or disclosures.

Fair Value Measurements

In June 2022 the FASB issued Accounting Standards Update (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 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 Therapeutics, Inc. (Sage).

Income Taxes

In December 2019 the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This standard removes certain exceptions to the general principles in Topic 740 and simplifies certain other aspects of the accounting for income taxes. This standard became effective for us on January 1, 2021, and did not have a material impact on our consolidated financial statements and related disclosures.

Acquisitions

12 Months Ended

Dec. 31, 2022

Business Combinations [Abstract]

Acquisitions


Note 2:			Acquisitions

BIIB118 Acquisition

In March 2020 we acquired BIIB118 (CK1 inhibitor) for the potential treatment of patients with behavioral and neurological symptoms across various psychiatric and neurological diseases from Pfizer Inc. (Pfizer). In connection with this acquisition, we made an upfront payment of $75.0 million to Pfizer, which was accounted for as an asset acquisition and recorded as acquired IPR&D in our consolidated statements of income for the year ended December 31, 2020. In 2022 we discontinued further development of BIIB118 based on the decision by management as part of its strategic review process.

Dispositions

12 Months Ended

Dec. 31, 2022

Divestitures [Abstract]

Dispositions


Note 3:			Dispositions

Sale of Joint Venture Equity Interest in Samsung Bioepis

In April 2022 we completed the sale of our 49.9% equity interest in Samsung Bioepis to Samsung BioLogics. Under the terms of this transaction, we received approximately $1.0 billion in cash at closing and expect to receive approximately $1.3 billion in cash to be deferred over two payments of approximately $812.5 million due at the first anniversary and approximately $437.5 million due at the second anniversary of the closing of this transaction.

Prior to the sale, the carrying value of our investment in Samsung Bioepis totaled $581.6 million. For the year ended December 31, 2022, we recognized a pre-tax gain of approximately $1.5 billion related to this transaction, which was recorded in other (income) expense, net in our consolidated statements of income. This pre-tax gain included reclassifications from accumulated other comprehensive income (loss) 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 have concluded that the divestment of Samsung Bioepis does not meet the criteria to be reported as discontinued operations in our consolidated financial statements, as our decision to divest this business does not represent a strategic shift that will have a major effect on our operations and financial results.

We elected the fair value option and measured the payments due to us from Samsung BioLogics at fair value. As of December 31, 2022, the estimated fair values of the first and second payments using risk-adjusted discount rates of 5.7% and 5.9%, respectively, were approximately $798.8 million and $405.4 million, respectively. These payments have been classified as level 3 measurements and are reflected in other current assets and investments and other assets, respectively, in our consolidated balance sheets.

For the year ended December 31, 2022, we recognized a gain of approximately $10.7 million and a loss of approximately $1.4 million to reflect the changes in fair value related to our first and second payments, respectively. These changes were recorded in other (income) expense, net in our consolidated statements of income.

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

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

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

Restructuring

12 Months Ended

Dec. 31, 2022

Restructuring and Related Activities [Abstract]

Restructuring


Note 4:			Restructuring

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, the consolidation of certain real estate locations and operating efficiency gains across our selling, general and administrative and research and development functions.

Under these initiatives, we estimate we will incur total restructuring charges of approximately $131.0 million, primarily related to severance. These amounts were substantially incurred during 2022. As of December 31, 2022, approximately $35.9 million remained in our restructuring reserve and payments are expected to be made through 2026.

For the year ended December 31, 2022, we recognized approximately $131.1 million of net pre-tax restructuring charges related to our 2022 cost saving initiatives, of which approximately $112.6 million consisted of employee severance costs. These costs were recorded in restructuring charges in our consolidated statements of income. Our restructuring reserve is included in accrued expense and other in our consolidated balance sheets.

In September 2022 we entered into an agreement to partially terminate a portion of our lease located at 300 Binney Street, Cambridge, MA (300 Binney Street), as well as to reduce the lease term for the majority of the remaining space. This resulted in a gain of approximately $5.3 million, which was recorded within restructuring charges in our consolidated statements of income for the year ended December 31, 2022. For additional information on our 300 Binney Street lease modification, please read Note 12, Leases, to these consolidated financial statements.

Following an evaluation of our current capacity needs, in March 2022 we ceased using a patient services office space in Durham, NC. Our decision to cease use of the facility resulted in the immediate expense of certain leasehold improvements and other assets at this facility. As a result, we recognized approximately $10.4 million of accelerated depreciation expense, which was recorded in restructuring charges in our consolidated statements of income for the year ended December 31, 2022. In May 2022 we entered into a lease assignment agreement whereby we assigned our remaining lease obligations to an external third party. As a result of the lease assignment, we derecognized the related operating lease obligation and right-of-use asset during the second quarter of 2022.

For the year ended December 31, 2022, we recognized other restructuring costs of approximately $13.2 million, which were recorded in restructuring charges in our consolidated statements of income. Other restructuring costs include items such as facility closure costs, employee non-severance expense, asset write-offs and other costs.

The following table summarizes the charges and spending related to our 2022 workforce reductions for the year ended December 31, 2022:


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

Revenue

12 Months Ended

Dec. 31, 2022

Revenue from Contract with Customer [Abstract]

Revenue


Note 5:			Revenue

Product Revenue

Revenue by product are summarized as follows:


	For the Years Ended December 31,
	2022						2021						2020
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis (MS):
TECFIDERA	$	417.7	$	1,026.2	$	1,443.9	$	680.6	$	1,271.3	$	1,951.9	$	2,677.7	$	1,163.4	$	3,841.1
VUMERITY(1)	521.3		32.1		553.4		408.9		1.5		410.4		64.3		—		64.3
Total Fumarate	939.0		1,058.3		1,997.3		1,089.5		1,272.8		2,362.3		2,742.0		1,163.4		3,905.4
AVONEX	649.2		324.3		973.5		830.2		378.5		1,208.7		1,083.4		408.5		1,491.9
PLEGRIDY	148.4		183.5		331.9		152.9		204.5		357.4		190.1		195.5		385.6
Total Interferon	797.6		507.8		1,305.4		983.1		583.0		1,566.1		1,273.5		604.0		1,877.5
TYSABRI	1,123.4		907.5		2,030.9		1,142.2		920.9		2,063.1		1,096.8		849.3		1,946.1
FAMPYRA	—		96.6		96.6		—		105.2		105.2		—		103.1		103.1
Subtotal: MS	2,860.0		2,570.2		5,430.2		3,214.8		2,881.9		6,096.7		5,112.3		2,719.8		7,832.1

Spinal Muscular Atrophy:
SPINRAZA	600.2		1,193.3		1,793.5		587.9		1,317.2		1,905.1		787.8		1,264.3		2,052.1

Biosimilars:
BENEPALI	—		441.0		441.0		—		498.3		498.3		—		481.6		481.6
IMRALDI	—		224.5		224.5		—		233.4		233.4		—		216.3		216.3
FLIXABI	—		81.3		81.3		—		99.4		99.4		—		97.9		97.9
BYOOVIZ(2)	4.3		—		4.3		—		—		—		—		—		—
Subtotal: Biosimilars	4.3		746.8		751.1		—		831.1		831.1		—		795.8		795.8

Other:
FUMADERM	—		8.2		8.2		—		11.0		11.0		—		12.2		12.2
ADUHELM	4.8		—		4.8		3.0		—		3.0		—		—		—
Total product revenue	$	3,469.3	$	4,518.5	$	7,987.8	$	3,805.7	$	5,041.2	$	8,846.9	$	5,900.1	$	4,792.1	$	10,692.2

(1) VUMERITY became commercially available in the E.U. during the fourth quarter of 2021.

(2) BYOOVIZ launched in the U.S. in June 2022 and became commercially available during the third quarter of 2022.

We recognized revenue from two wholesalers accounting for 26.8% and 11.1% of gross product revenue in 2022, 28.8% and 10.1% of gross product revenue in 2021 and 30.5% and 15.3% of gross product revenue in 2020, respectively.

As of December 31, 2022, two wholesale distributors individually accounted for approximately 22.7% and 10.9% of net accounts receivable associated with our product sales, as compared to 21.9% and 10.2% as of December 31, 2021, respectively.

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


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


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


	December 31, 2020
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	131.1	$	1,027.3	$	40.5	$	1,198.9
Current provisions relating to sales in current year	774.7		3,308.8		19.0		4,102.5
Adjustments relating to prior years	(1.0)		(54.0)		1.3		(53.7)
Payments/credits relating to sales in current year	(635.1)		(2,426.1)		—		(3,061.2)
Payments/credits relating to sales in prior years	(128.3)		(763.0)		(19.2)		(910.5)
Ending balance	$	141.4	$	1,093.0	$	41.6	$	1,276.0

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


	As of December 31,
(In millions)	2022		2021
Reduction of accounts receivable	$	143.4	$	133.2
Component of accrued expense and other	891.6		802.1
Total revenue-related reserves	$	1,035.0	$	935.3

Revenue from Anti-CD20 Therapeutic Programs

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Royalty revenue on sales of OCREVUS	$	1,136.3	$	991.7	$	845.4
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0		647.7		1,080.2
Other revenue from anti-CD20 therapeutic programs	17.2		19.1		52.2
Total revenue from anti-CD20 therapeutic programs	$	1,700.5	$	1,658.5	$	1,977.8

Approximately 16.7%, 15.1% and 14.7% of our total revenue in 2022, 2021 and 2020, respectively, was derived from our collaboration arrangements with Genentech. For additional information on our collaboration

arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Other Revenue

Other revenue consists of royalty revenue and contract manufacturing and other revenue and is summarized as follows:


	For the Years Ended December 31,
(In millions)	2022		2021		2020




Contract manufacturing and other revenue	$	417.7	$	427.7	$	719.1
Royalty revenue	67.4		48.6		55.5
Total other revenue	$	485.1	$	476.3	$	774.6

Contract Manufacturing and Other Revenue

Contract manufacturing and other revenue primarily reflects amounts earned under contract manufacturing agreements with our strategic customers.

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

Contract manufacturing and other revenue for the year ended December 31, 2020, reflects $346.2 million related to the delivery of the license for certain of our manufacturing-related intellectual property under the amended agreement, as discussed above, and the performance of manufacturing product supply services for such customer. We allocated the remaining $153.8 million of the $500.0 million transaction price to the performance of manufacturing product supply services for the customer, which we expect to perform through 2026. The value allocated to the manufacturing services was based on expected demand for supply and the fair value of comparable manufacturing and development services.

Royalty Revenue

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

- Definition

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

+ References

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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Inventory

12 Months Ended

Dec. 31, 2022

Inventory Disclosure [Abstract]

Inventory


Note 6:			Inventory

The components of inventory are summarized as follows:


	As of December 31,
(In millions)	2022		2021
Raw materials	$	413.2	$	349.6
Work in process(1)	751.9		814.0
Finished goods	200.4		187.9
Total inventory	$	1,365.5	$	1,351.5

Balance Sheet Classification:
Inventory	$	1,344.4	$	1,351.5
Investments and other assets	21.1		—
Total inventory	$	1,365.5	$	1,351.5

(1) Work in process inventory as of December 31, 2022, includes approximately $89.8 million related to LEQEMBI.

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

Inventory amounts written down as a result of excess, obsolescence or unmarketability are charged to cost of sales, and totaled $336.2 million, $167.6 million and $26.6 million for the years ended December 31, 2022, 2021 and 2020, respectively.

Inventory Write-Offs

In April 2022 the Centers for Medicare and Medicaid Services (CMS) released the final National Coverage Decision (NCD) for the class of anti-amyloid treatments in Alzheimer's disease, including ADUHELM. The final NCD confirmed coverage with evidence development, in which patients with Medicare can only access treatment if they are part of an approved clinical trial. We expect that this decision will reduce future demand for ADUHELM to a minimal level. During the first quarter of 2022 we wrote-off approximately $275.0 million of inventory related to ADUHELM, as a result of this CMS decision, which was recognized in cost of sales within our consolidated statements of income for the year ended December 31, 2022. We have recognized approximately $136.0 million related to Eisai's 45.0% share of these charges in collaboration profit (loss) sharing within our consolidated statements of income for the year ended December 31, 2022.

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

As of December 31, 2022, the carrying value of our ADUHELM inventory was immaterial. As of December 31, 2021, we had approximately $223.0 million of ADUHELM inventory. For additional information please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Intangible Assets and Goodwill

12 Months Ended

Dec. 31, 2022

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets and Goodwill


Note 7:			Intangible Assets and Goodwill

Intangible Assets

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


		As of December 31, 2022						As of December 31, 2021
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology	4-28 years	$	7,415.3	$	(5,629.2)	$	1,786.1	$	7,413.1	$	(5,388.5)	$	2,024.6
In-process research and development	Indefinite until commercialization	—		—		—		132.7		—		132.7
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	7,479.3	$	(5,629.2)	$	1,850.1	$	7,609.8	$	(5,388.5)	$	2,221.3

Amortization and Impairments

Amortization and impairment of acquired intangible assets totaled $365.9 million, $881.3 million and $464.8 million for the years ended December 31, 2022, 2021 and 2020, respectively.

Amortization of acquired intangible assets, excluding impairment charges, totaled $246.3 million, $252.0 million and $255.1 million for the years ended December 31, 2022, 2021 and 2020, respectively. The decrease in amortization of acquired intangible assets, excluding impairment charges, over the three years was primarily due to a lower rate of amortization for acquired intangible assets.

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

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

For the year ended December 31, 2020, amortization and impairment of acquired intangible assets reflects the impact of a $115.0 million impairment charge related to BIIB111, a $75.4 million impairment charge related to BIIB054 (cinpanemab) and a $19.3 million impairment charge related to one of our other IPR&D intangible assets.

Completed Technology

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

IPR&D Related to Business Combinations

IPR&D represents the fair value assigned to research and development assets that we acquired as part of a business combination and had not yet reached technological feasibility at the date of acquisition. Included in IPR&D balances are adjustments related to foreign currency exchange rate fluctuations. We review amounts capitalized as acquired IPR&D for impairment annually, as of October 31, and whenever events or changes in circumstances indicate to us that the carrying value of the assets might not be recoverable. The carrying value associated with our IPR&D assets as of December 31, 2021, relates to the IPR&D programs we acquired in connection with our acquisition of Convergence Pharmaceuticals Holdings Ltd. (Convergence). As of December 31, 2022, as a result of our decision to discontinue development of vixotrigine, we recognized an impairment charge reducing the remaining book value to zero.

Vixotrigine

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

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

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

BIIB111 and BIIB112

In connection with our acquisition of Nightstar Therapeutics plc, we recognized $480.0 million and $220.0 million of acquired IPR&D intangible assets for BIIB111 and BIIB112, respectively. During the fourth quarter of 2020 we recognized an impairment charge of $115.0 million related to BIIB111 as a result of third-party manufacturing delays that impacted the timing and increased the costs associated with advancing BIIB111 through Phase 3 development.

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

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

BIIB054

In connection with our acquisition of Biogen International Neuroscience GmbH (BIN), we recognized a $110.9 million acquired IPR&D intangible asset. In February 2021 we announced that we discontinued development of BIIB054 as a potential treatment of Parkinson's disease as our Phase 2 SPARK study did not meet its primary or secondary endpoints. Although we made this determination in February 2021, it was based on conditions that existed as of December 31, 2020. As a result, we recognized an impairment charge of approximately $75.4 million during the fourth quarter of 2020 to reduce the fair value of the related IPR&D intangible asset to zero.

The IPR&D impairment charges were included in amortization and impairment of acquired intangible assets and the gain resulting from the remeasurement of our contingent consideration obligation was recorded in (gain) loss on fair value remeasurement of contingent consideration in our consolidated statements of income. The fair value of the intangible assets and contingent consideration obligations were based on a probability-adjusted discounted cash flow calculation using Level 3 fair value measurements and inputs including estimated revenue, costs and probabilities of success.

Estimated Future Amortization of Intangible Assets

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


(In millions)	As of December 31, 2022
2023	$	215.0
2024	195.0
2025	190.0
2026	175.0
2027	165.0

Goodwill

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


	As of December 31,
(In millions)	2022		2021
Goodwill, beginning of year	$	5,761.1	$	5,762.1


Other	(12.1)		(1.0)
Goodwill, end of year	$	5,749.0	$	5,761.1

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

Fair Value Measurements

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value Measurements


Note 8:			Fair Value Measurements

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


	As of December 31, 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 consolidated financial statements.


	As of December 31, 2021
(In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	1,632.2	$	—	$	1,632.2	$	—
Marketable debt securities:
Corporate debt securities	1,108.2		—		1,108.2		—
Government securities	1,192.7		—		1,192.7		—
Mortgage and other asset backed securities	132.2		—		132.2		—
Marketable equity securities	1,048.5		181.7		866.8		—
Derivative contracts	80.9		—		80.9		—
Plan assets for deferred compensation	33.4		—		33.4		—
Total	$	5,228.1	$	181.7	$	5,046.4	$	—
Liabilities:
Derivative contracts	$	10.8	$	—	$	10.8	$	—
Contingent consideration obligations	209.1		—		—		209.1
Total	$	219.9	$	—	$	10.8	$	209.1

The fair value of Level 2 instruments classified as cash equivalents and marketable debt securities was determined through third-party pricing services. In the third quarter of 2022 we elected to early adopt ASU 2022-03 on a prospective basis, which resulted in removing the impact of contractual sale restrictions from the fair value measurement of our remaining Sage common stock subject to certain holding period restrictions. As of December 31, 2022, our entire investment in the common stock of Sage was classified as a Level 1 measurement. Prior to the adoption of this standard, the fair value of Level 2 instruments classified as marketable equity securities represented a portion of our investment in the common stock of Sage and was valued using an option pricing valuation model.

Our investments in the common stock of Sangamo Therapeutics, Inc. (Sangamo) and Denali Therapeutics Inc. (Denali) had holding period restrictions that expired during 2022. As of December 31, 2022, the fair values of our investments in Sangamo and Denali common stock were classified as Level 1 measurements. Prior to the expiration of these holding period restrictions the investments were classified as Level 2 measurements.

Although the contractual holding period restrictions on our investments in Denali, Sage and Sangamo have expired, our ability to liquidate these investments may be limited by the size of our interest, the volume of market related activity, our concentrated level of ownership and potential restrictions resulting from our status as a collaborator. Therefore, we may realize significantly less than the current value of such investments.

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

There have been no material impairments of our assets measured and carried at fair value as of December 31, 2022 and 2021. In addition, there have been no changes in valuation techniques as of December 31, 2022 and 2021.

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

Level 3 Assets and Liabilities Held at Fair Value

The following table presents quantitative information, as of the dates indicated, about the valuation techniques and significant unobservable inputs used in the valuation of our level 3 financial assets and liabilities measured at fair value on a recurring basis:


	Quantitative Information about Level 3 Fair Value Measurements
	Fair Value					Significant Unobservable Input(s)	Range	Weighted Average
(In millions)	2022(1)		2021		Valuation Technique		2021	2022(1)		2021




Liabilities:
Contingent consideration obligations	$	—	$	209.1	Discounted cash flow	Discount rate	1.30%	—	%	1.30	%
						Expected timing of achievement of development milestones	2023 to 2027	—		—

(1) During the year ended December 31, 2022, we discontinued the development of vixotrigine and as a result we adjusted the fair value of our contingent consideration obligations to zero.

The weighted average discount rates were calculated based on the relative fair value of our contingent consideration obligations. In addition, we apply various probabilities of technological and regulatory success to the valuation models to estimate the fair values of our contingent consideration obligations, which ranged from 10.9% to certain probability as of December 31, 2021.

There were no transfers of assets or liabilities into or out of Level 3 as of December 31, 2022 and 2021.

Contingent Consideration Obligations

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


	As of December 31,
(In millions)	2022		2021
Fair value, beginning of year	$	209.1	$	259.8
Changes in fair value	(209.1)		(50.7)

Fair value, end of year	$	—	$	209.1

As of December 31, 2021, approximately $209.1 million of the fair value of our total contingent consideration obligations was reflected as a component of other long-term liabilities in our consolidated balance sheets. Changes in the fair values of our contingent consideration obligations are recorded in (gain) loss on fair value remeasurement of contingent consideration in our consolidated statements of income.

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

For the year ended December 31, 2021, the changes in fair value of our contingent consideration obligations were primarily due to reductions in the probability of technical and regulatory success and delays in the expected timing of the achievement of certain remaining developmental milestones related to our vixotrigine programs.

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

Convergence Pharmaceuticals Holdings Limited

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

Biogen International Neuroscience GmbH

In connection with our acquisition of BIN in December 2010 we recorded a contingent consideration obligation of $81.2 million. We discontinued further development of BIIB054 for the potential treatment of Parkinson's disease based on the results of a Phase 2 study of BIIB054. Additionally, during the third and fourth quarters of 2020 we discontinued other programs related to our acquisition of BIN for which we had immaterial contingent consideration obligations. As a result, the fair value of the contingent consideration obligations related to our acquisition of BIN was adjusted to zero, resulting in a gain of $101.5 million for the year ended December 31, 2020. This pre-tax gain was recorded in (gain) loss on fair value remeasurement of contingent consideration within our consolidated statements of income.

Nonrecurring Fair Value Measurements

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

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

Financial Instruments Not Carried at Fair Value

Other Financial Instruments

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

Debt Instruments

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


	Fair Value As of December 31,
(In millions)	2022		2021
3.625% Senior Notes due September 15, 2022(1)	$	—	$	1,020.0
4.050% Senior Notes due September 15, 2025	1,699.9		1,895.2
2.250% Senior Notes due May 1, 2030	1,219.0		1,475.9
5.200% Senior Notes due September 15, 2045	1,033.2		1,463.0
3.150% Senior Notes due May 1, 2050	989.0		1,457.7
3.250% Senior Notes due February 15, 2051	469.1		692.9
Total	$	5,410.2	$	8,004.7

(1) In July 2022 we redeemed our 3.625% Senior Notes due September 15, 2022 in full. For additional information on the redemption, please read Note 13, Indebtedness, to these consolidated financial statements.

The fair values of each of our series of Senior Notes were determined through market, observable and corroborated sources. The changes in the fair values of our Senior Notes as of December 31, 2022, compared to 2021, are primarily related to increases in U.S. treasury yields used to value our Senior Notes since December 31, 2021. For additional information related to our Senior Notes, please read Note 13, Indebtedness, to these consolidated financial statements.

- Definition

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

+ References + Details

Financial Instruments

12 Months Ended

Dec. 31, 2022

Investments, All Other Investments [Abstract]

Financial Instruments


Note 9:			Financial Instruments

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


	As of December 31,
(In millions)	2022		2021
Commercial paper	$	177.2	$	247.6
Overnight reverse repurchase agreements	59.0		200.0
Money market funds	2,581.5		901.6
Short-term debt securities	29.9		283.0
Total	$	2,847.6	$	1,632.2

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.

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


	As of December 31, 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, current	$	1,133.8	$	—	$	(342.7)	$	791.1

Total marketable equity securities	$	1,133.8	$	—	$	(342.7)	$	791.1


	As of December 31, 2021
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable debt securities:
Corporate debt securities:
Current	$	723.6	$	0.1	$	(0.3)	$	723.4
Non-current	385.4		0.2		(0.8)		384.8
Government securities:
Current	817.0		—		(0.4)		816.6
Non-current	377.0		0.1		(1.0)		376.1
Mortgage and other asset backed securities:
Current	1.1		—		—		1.1
Non-current	131.8		—		(0.7)		131.1
Total marketable debt securities	$	2,435.9	$	0.4	$	(3.2)	$	2,433.1

Marketable equity securities:
Marketable equity securities, current	$	33.9	$	9.9	$	—	$	43.8
Marketable equity securities, non-current	1,133.1		151.0		(279.4)		1,004.7
Total marketable equity securities	$	1,167.0	$	160.9	$	(279.4)	$	1,048.5

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				2021
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	1,473.5	$	1,483.3	$	1,541.1	$	1,541.7
Due after one year through five years	694.4		703.7		868.2		870.2
Due after five years	11.3		12.1		23.8		24.0
Total marketable debt securities	$	2,179.2	$	2,199.1	$	2,433.1	$	2,435.9

The average maturity of our marketable debt securities classified as available-for-sale as of December 31, 2022 and 2021, was approximately 8 months and 10 months, respectively.

Proceeds from Marketable Debt Securities

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Proceeds from maturities and sales	$	3,671.0	$	3,405.4	$	7,299.4
Realized gains	—		0.2		17.7
Realized losses	12.6		4.0		26.0

Realized losses for the year ended December 31, 2022, 2021 and 2020, primarily relate to sales of corporate bonds, agency mortgage-backed securities and other asset-backed securities.

Strategic Investments

As of December 31, 2022, our strategic investment portfolio comprised of investments totaling $846.0 million which are included in investments and other assets in our consolidated balance sheets. As of December 31, 2021, our strategic investment portfolio comprised of investments totaling $1,110.3 million, which are included in other current assets and investments and other assets in our consolidated balance sheets.

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

The decrease in our strategic investment portfolio for the year ended December 31, 2022, was primarily due to a decrease in the fair value of our investments in Denali and Sangamo common stock.

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

Derivative Instruments

12 Months Ended

Dec. 31, 2022

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments


Note 10:			Derivative Instruments

Foreign Currency Forward Contracts - Hedging Instruments

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

Foreign currency forward contracts and foreign currency options in effect as of December 31, 2022 and 2021, had durations of 1 to 12 months and 1 to 15 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 accumulated other comprehensive income (loss) (referred to as AOCI in the table below). Realized gains and losses of such contracts 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 accumulated other comprehensive income (loss) and fair value changes of excluded portions in the same line item in our consolidated statements of income that have been impacted by the hedged item.

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


	Notional Amount As of December 31,
(In millions)	2022		2021
Euro	$	1,495.5	$	1,828.0
British pound	162.8		166.2

Japanese yen	—		72.7
Canadian dollar	57.2		59.9
Total foreign currency forward contracts	$	1,715.5	$	2,126.8

The pre-tax portion of the fair value of these foreign currency forward contracts and foreign currency options that were included in accumulated other comprehensive income (loss) in total equity is summarized as follows:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Unrealized gains	$	29.9	$	60.8	$	—
Unrealized (losses)	(21.3)		(7.0)		(212.5)
Net unrealized gains (losses)	$	8.6	$	53.8	$	(212.5)

We expect the net unrealized gains of approximately $8.6 million to be settled over the next 12 months, with any amounts in accumulated other comprehensive income (loss) to be reported as an adjustment to revenue or operating expense. We consider the impact of our and our counterparties’ credit risk on the fair value of the contracts as well as the ability of each party to execute its contractual obligations. As of December 31, 2022 and 2021, credit risk did not materially change the fair value of our foreign currency forward contracts.

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


For the Years Ended December 31,
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)							Net Gains/(Losses) Recognized in Operating Income (in millions)
Location	2022		2021		2020		Location	2022		2021		2020
Revenue	$	201.6	$	(60.0)	$	18.3	Revenue	$	(8.6)	$	(8.4)	$	(9.9)
Operating expense	(5.5)		(0.8)		3.3		Operating expense	—		—		—

Interest Rate Contracts - Hedging Instruments

We have entered into interest rate lock contracts or interest rate swap contracts on certain borrowing transactions to manage our exposure to interest rate changes and to reduce our overall cost of borrowing.

Interest Rate Swap Contracts

In connection with the issuance of our 2.90% Senior Notes due September 15, 2020, we entered into interest rate swaps with an aggregate notional amount of $675.0 million, which were originally set to expire on September 15, 2020. The interest rate swap contracts were designated as hedges of the fair value changes in our 2.90% Senior Notes attributable to changes in interest rates. In May 2020 we settled our interest rate swap contracts, in conjunction with our early redemption of our 2.90% Senior Notes, resulting in a gain of approximately $3.3 million, which was recorded as a component of interest expense in our consolidated statements of income during the year ended December 31, 2020.

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%. The share purchase transaction was completed in November 2018 and, upon closing, we paid 759.5 billion South Korean won ($676.6 million) to Samsung BioLogics. 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 these 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 accumulated other comprehensive income (loss) and reflected within the total pre-tax gain recognized from the sale, which was recorded in other (income) expense, net in our consolidated statements of income. For additional information on the sale of our equity interest in Samsung Bioepis please read Note 3, Dispositions, to these consolidated financial statements.

Prior to the sale of our 49.9% equity interest in Samsung Bioepis, we recognized changes in the spot exchange rate of these foreign currency forward contracts in accumulated other comprehensive income (loss). The pre-tax portion of the fair value of these foreign currency forward contracts that were included in accumulated other comprehensive income (loss) in total equity reflected net gains of $10.6 million as of December 31, 2021. We excluded fair value changes related to the forward rate from our hedging relationship and amortized the forward points in other (income) expense, net in our consolidated statements of income over the term of the contract. The pre-tax portion of the fair value of the forward points that were included in accumulated other comprehensive income (loss) in total equity reflected net losses of $3.6 million as of December 31, 2021.

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


For the Years Ended December 31,
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion) (in millions)							Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions)							Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)
Location	2022		2021		2020		Location	2022		2021		2020		Location	2022		2021		2020
Gains (losses) on net investment hedge(1)	$	20.4	$	46.0	$	(35.1)	Gains (losses) on net investment hedge(1)	$	(3.2)	$	(3.2)	$	4.5	Other (income) expense(1)	$	(4.6)	$	(0.6)	$	2.9

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

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

Foreign Currency Forward Contracts - Other Derivative Instruments

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

The aggregate notional amount of these outstanding foreign currency forward contracts was $1,238.8 million and $1,268.0 million as of December 31, 2022 and 2021, respectively. Net losses of $34.7 million, net losses of $43.3 million and net gains of $30.1 million related to these contracts were recorded as a component of other (income) expense, net for the years ended December 31, 2022, 2021 and 2020, respectively.

Summary of Derivative Instruments

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

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


		As of December 31,
(In millions)	Balance Sheet Location	2022		2021
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	37.9	$	66.2
	Investments and other assets	—		5.5
Liability derivative instruments	Accrued expense and other	18.4		6.6


Net Investment Hedging Instruments:(1)
Asset derivative instruments	Other current assets	—		4.1






Other Derivative Instruments:
Asset derivative instruments	Other current assets	25.1		5.1
Liability derivative instruments	Accrued expense and other	7.6		4.2

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment


Note 11:			Property, Plant and Equipment

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


	As of December 31,
(In millions)	2022		2021
Land	$	202.4	$	207.5
Buildings	1,592.9		1,699.7
Leasehold improvements	107.7		121.0
Machinery and equipment	1,611.5		1,585.5
Computer software and hardware	999.9		971.6
Furniture and fixtures	61.1		67.4
Construction in progress	888.8		770.3
Total cost	5,464.3		5,423.0
Less: accumulated depreciation	(2,165.7)		(2,006.6)
Total property, plant and equipment, net	$	3,298.6	$	3,416.4

Depreciation expense totaled $272.4 million, $235.3 million and $201.9 million for the years ended December 31, 2022, 2021 and 2020, respectively.

For the years ended December 31, 2022, 2021 and 2020, we capitalized interest costs related to construction in progress totaling approximately $17.1 million, $36.3 million and $65.2 million, respectively.

Solothurn, Switzerland Manufacturing Facility

In order to support our future growth and drug development pipeline, we are building a large-scale biologics manufacturing facility in Solothurn, Switzerland. Upon completion, 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 December 31, 2022 and 2021, we had approximately $711.1 million and $677.0 million, respectively, capitalized as construction in progress related to this facility. In the second quarter of 2021 a portion of the facility received a Good Manufacturing Practice multi-product license from the Swiss Agency for Therapeutic Products, resulting in approximately $1.2 billion of fixed assets being placed in service during the second quarter of 2021. Solothurn has been approved for the manufacture of ADUHELM and

LEQEMBI by the FDA. We estimate the second manufacturing suite at the Solothurn facility 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 consolidated statements of income for the year ended December 31, 2022. This transaction included approximately $79.2 million of property, plant and equipment, net, which comprised of approximately $72.6 million for buildings, approximately $1.6 million for land and approximately $5.0 million for machinery and equipment.

Leases

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Leases


Note 12:			Leases

We lease real estate, including laboratory and office space, and certain equipment.

Our leases have remaining lease terms ranging from less than one year to eight years. Certain leases include one or more options to renew, exercised at our sole discretion, with renewal terms that can extend the lease term from one year to six years.

In addition, we sublease certain real estate to third parties. Our sublease portfolio consists of operating leases, with remaining lease terms ranging from two years to six years. Our subleases do not include an option to renew as they are coterminous with our operating leases.

All of our leases qualify as operating leases. The following table summarizes the presentation in our consolidated balance sheets of our operating leases:


		As of December 31,
(In millions)	Balance sheet location	2022		2021
Assets:
Operating lease assets	Operating lease assets	$	403.9	$	375.4

Liabilities
Current operating lease liabilities	Accrued expense and other	$	97.2	$	89.1
Non-current operating lease liabilities	Long-term operating lease liabilities	333.0		330.4
Total operating lease liabilities		$	430.2	$	419.5

The following table summarizes the effect of lease costs in our consolidated statements of income:


		For the Years Ended December 31,
(In millions)	Income Statement Location	2022		2021		2020
Operating lease cost	Research and development	$	2.0	$	3.4	$	5.2
	Selling, general and administrative	95.9		95.9		93.1
Variable lease cost	Research and development	0.4		0.8		1.1
	Selling, general and administrative	25.4		25.7		21.1
Sublease income	Selling, general and administrative	(24.0)		(23.9)		(24.2)
	Other (income) expense, net	(4.1)		(4.0)		(3.9)
Net lease cost		$	95.6	$	97.9	$	92.4

Variable lease cost primarily related to operating expense, taxes and insurance associated with our operating leases. As these costs are generally variable in nature, they are not included in the measurement of the operating lease asset and related lease liability.

The minimum lease payments for the next five years and thereafter is expected to be as follows:


(In millions)	As of December 31, 2022
2023	$	111.0
2024	107.0
2025	80.5
2026	65.7
2027	69.5
Thereafter	36.6
Total lease payments	$	470.3
Less: interest	40.1
Present value of operating lease liabilities	$	430.2

The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows:


	As of December 31,
	2022		2021
Weighted average remaining lease term in years	4.64		5.43
Weighted average discount rate	3.7	%	2.9	%

Supplemental disclosure of cash flow information related to our operating leases included in cash flow provided by operating activities in our consolidated statements of cash flow is as follows:


	As of December 31,
(In millions)	2022		2021		2020
Cash paid for amounts included in the measurement of lease liabilities	$	107.4	$	105.8	$	100.2
Operating lease assets obtained in exchange for lease obligations	108.3		18.1		59.0

125 Broadway Building Sale and Leaseback Transaction

In connection with the sale of our building at 125 Broadway, 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 new lease liabilities and right-of-use assets recorded within our consolidated balance sheets as of December 31, 2022. The sale and immediate leaseback of this building qualified for sale and leaseback treatment and is classified as an operating lease. For additional information on the sale of our building, please read Note 11, Property, Plant and Equipment, to these consolidated financial statements.

300 Binney Street Lease Modification

In September 2022 we entered into an agreement to partially terminate a portion of our lease located at 300 Binney Street, Cambridge MA, 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 right of use assets of approximately $47.4 million and lease liabilities of approximately $52.7 million, which resulted in a gain of approximately $5.3 million, which was recorded within restructuring charges in our consolidated statements of income for the year ended December 31, 2022.

Indebtedness

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Indebtedness


Note 13:			Indebtedness

Our indebtedness is summarized as follows:


	As of December 31,
(In millions)	2022		2021
Current portion:
3.625% Senior Notes due September 15, 2022(1)	$	—	$	999.1
Current portion of notes payable	$	—	$	999.1
Non-current portion:
4.050% Senior Notes due September 15, 2025	$	1,744.7	$	1,742.9
2.250% Senior Notes due May 1, 2030	1,492.9		1,492.0
5.200% Senior Notes due September 15, 2045	1,100.3		1,099.9
3.150% Senior Notes due May 1, 2050	1,473.8		1,473.2
3.250% Senior Notes due February 15, 2051	469.3		466.0
Non-current portion of notes payable	$	6,281.0	$	6,274.0

(1) Our 3.625% Senior Notes due September 15, 2022, were redeemed in full in July 2022.

Exchange Offer

In February 2021 we completed our private offer to exchange (Exchange Offer) our tendered 5.200% Senior Notes due September 15, 2045 (2045 Senior Notes) for a new series of 3.250% Senior Notes due February 15, 2051 (2051 Senior Notes) and cash, and an offer to purchase our tendered 2045 Senior Notes for cash.

An aggregate principal amount of approximately $624.6 million of our 2045 Senior Notes was exchanged for an aggregate principal amount of approximately $700.7 million of our 2051 Senior Notes and aggregate cash payments of approximately $151.8 million. Our Exchange Offer has been accounted for as a debt modification; as such, the cash component has been reflected as additional debt discount and is amortized as an adjustment to interest expense over the term of our 2051 Senior Notes.

In addition, we redeemed an aggregate principal amount of approximately $8.9 million of our 2045 Senior Notes for aggregate cash payments of approximately $12.1 million, excluding accrued and unpaid interest. The redemption has been accounted for as a debt extinguishment; as such, we recognized a pre-tax charge of $3.2 million upon the extinguishment of such 2045 Senior Notes. This charge, which was recognized in interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2021, reflects the payment of an early call premium and the write-off of the remaining unamortized original debt issuance costs and discount balances associated with such 2045 Senior Notes.

Upon settlement, we also made aggregate cash payments of approximately $13.8 million to settle all accrued and unpaid interest from the last interest payment date on our 2045 Senior Notes that were exchanged or redeemed. We incurred approximately $6.1 million of costs associated with our Exchange Offer, which was recognized in interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2021.

2020 Senior Notes

On April 30, 2020, we issued senior unsecured notes for an aggregate principal amount of $3.0 billion (2020 Senior Notes), consisting of the following:

•$1.5 billion aggregate principal amount of 2.25% Senior Notes due May 1, 2030, valued at 99.973% of par; and

•$1.5 billion aggregate principal amount of 3.15% Senior Notes due May 1, 2050, valued at 99.174% of par.

Our 2020 Senior Notes are senior unsecured obligations and may be redeemed at our option at any time at 100.0% of the principal amount plus accrued interest and, until a specified period before maturity, a specified make-whole amount. Our 2020 Senior Notes contain a change-of-control provision that, under certain circumstances, may require us to purchase our 2020 Senior Notes at a price equal to 101.0% of the principal amount plus accrued and unpaid interest to the date of repurchase.

We incurred approximately $24.4 million of costs associated with this offering, which have been recorded as a reduction to the carrying amount of the debt on our consolidated balance sheet. These costs will be amortized as additional interest expense using the effective interest rate method over the period from issuance through maturity. The discounts will be amortized as additional interest expense over the period from issuance through maturity using the effective interest rate method. Interest on our 2020 Senior Notes is payable May 1 and November 1 of each year, commencing November 1, 2020.

2015 Senior Notes

The following is a summary of our currently outstanding senior unsecured notes issued in 2015 (the 2015 Senior Notes), consisting of the following:

•$1.75 billion aggregate principal amount of 4.05% Senior Notes due September 15, 2025, valued at 99.764% of par; and

•$1.12 billion aggregate principal amount of 5.20% Senior Notes due September 15, 2045, valued at 99.294% of par.

The original costs associated with this offering of approximately $47.5 million have been recorded as a reduction to the carrying amount of the debt in our consolidated balance sheets. These costs along with the discounts will be amortized as additional interest expense using the effective interest rate method over the period from issuance through maturity.

Our 2015 Senior Notes are senior unsecured obligations and may be redeemed at our option at any time at 100.0% of the principal amount plus accrued interest and a specified make-whole amount. Our 2015 Senior Notes contain a change of control provision that may require us to purchase the notes at a price equal to 101.0% of the principal amount plus accrued and unpaid interest to the date of purchase under certain circumstances.

On September 15, 2015, we issued $1.5 billion aggregate principal amount of 2.90% Senior Notes due September 15, 2020, at 99.792% of par. Our 2.90% Senior Notes were senior unsecured obligations. In connection with the 2.90% Senior Notes, we entered into interest rate swap contracts where we received a fixed rate and paid a variable rate. In May 2020 we used the net proceeds from the sale of our 2020 Senior Notes to redeem our 2.90% Senior Notes prior to their maturity and recognized a net pre-tax charge of $9.4 million upon the extinguishment of these notes. This charge, which was recognized in interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2020, reflects the payment of a $12.7 million early call premium and the write off of remaining unamortized original debt issuance costs and discount balances, partially offset by a $3.3 million gain related to the settlement of the associated interest rate swap contracts. For additional information on our interest rate contracts, please read Note 10, Derivative Instruments, to these consolidated financial statements.

3.625% Senior Notes due September 15, 2022

On September 15, 2015, we issued $1.0 billion aggregate principal amount of our 3.625% Senior Notes due September 15, 2022, at 99.920% of par. Our 3.625% Senior Notes were senior unsecured obligations. In July 2022 we redeemed our 3.625% Senior Notes prior to their maturity and recognized a net pre-tax charge of approximately $2.4 million upon the extinguishment of these Senior Notes, which primarily reflects the payment of an early call premium as well as the write-off of remaining unamortized original debt issuance costs and discount balances.

These charges were recognized as interest expense in other (income) expense, net in our consolidated statements of income for the year ended December 31, 2022.

2020 Credit Facility

In January 2020 we entered into a $1.0 billion, five-year senior unsecured revolving credit facility under which we are permitted to draw funds for working capital and general corporate purposes. The terms of the revolving credit facility include a financial covenant that requires us not to exceed a maximum consolidated leverage ratio. This revolving credit facility replaced the revolving credit facility that we entered into in August 2015. As of December 31, 2022, we had no outstanding borrowings and were in compliance with all covenants under this facility.

Debt Maturity

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


(In millions)	As of December 31, 2022
2023	$	—
2024	—
2025	1,750.0
2026	—
2027	—
2028 and thereafter	4,817.3
Total debt	$	6,567.3
Less: debt discount and issuance fees	(286.3)
Total long-term debt	$	6,281.0

The fair value of our debt is disclosed in Note 8, Fair Value Measurements, to these consolidated financial statements.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

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+ Details

Equity

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Equity


Note 14:			Equity

Preferred Stock

We have 8.0 million shares of Preferred Stock authorized, of which 1.75 million shares are authorized as Series A, 1.0 million shares are authorized as Series X junior participating and 5.25 million shares are undesignated. Shares may be issued without a vote or action of shareholders from time to time in classes or series with the designations, powers, preferences and the relative, participating, optional or other special rights of the shares of each such class or series and any qualifications, limitations or restrictions thereon as set forth in the instruments governing such shares. Any such Preferred Stock may rank prior to common stock as to dividend rights, liquidation preference or both, and may have full or limited voting rights and may be convertible into shares of common stock. No shares of Preferred Stock were issued and outstanding during 2022, 2021 and 2020.

Common Stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2022, 2021 and 2020:

As of December 31, 2022

As of December 31, 2021

As of December 31, 2020

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

167.9

144.0

1,000.0

170.8

147.0

1,000.0

176.2

152.4

Share Repurchases

In October 2020 our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (2020 Share Repurchase Program). Our 2020 Share Repurchase Program does not have an expiration date. All share repurchases under our 2020 Share Repurchase Program will be retired. Under our 2020 Share Repurchase Program, we repurchased and retired approximately 3.6 million, 6.0 million and 1.6 million shares of our common stock at a cost of approximately $750.0 million, $1.8 billion and $400.0 million during the years ended December

31, 2022, 2021 and 2020, respectively. Approximately $2.1 billion remained available under our 2020 Share Repurchase Program as of December 31, 2022.

In December 2019 our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (December 2019 Share Repurchase Program), which was completed as of September 30, 2020. All shares repurchased under our December 2019 Share Repurchase Program were retired. Under our December 2019 Share Repurchase Program, we repurchased and retired approximately 16.7 million shares of our common stock at a cost of approximately $5.0 billion during the year ended December 31, 2020.

In March 2019 our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (March 2019 Share Repurchase Program), which was completed as of March 31, 2020. All shares repurchased under our March 2019 Share Repurchase Program were retired. Under our March 2019 Share Repurchase Program, we repurchased and retired approximately 4.1 million shares of our common stock at a cost of approximately $1.3 billion during the year ended December 31, 2020.

In August 2022 the Inflation Reduction Act of 2022 (the IRA) was signed into law. Among other things, the IRA levies a 1.0% excise tax on net stock repurchases after December 31, 2022. Historically, we have made discretionary share repurchases.

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

Accumulated Other Comprehensive Income (Loss)

The following tables summarize the changes in accumulated other comprehensive income (loss), net of tax by component:


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


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


	December 31, 2020
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Gains (Losses) on Net Investment Hedges, Net of Tax		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2019	$	4.2	$	7.8	$	25.1	$	(32.8)	$	(139.5)	$	(135.2)
Other comprehensive income (loss) before reclassifications	(9.3)		(165.0)		(30.7)		(33.5)		92.9		(145.6)
Amounts reclassified from accumulated other comprehensive income (loss)	6.5		(21.8)		(2.9)		—		—		(18.2)
Net current period other comprehensive income (loss)	(2.8)		(186.8)		(33.6)		(33.5)		92.9		(163.8)
Balance, December 31, 2020	$	1.4	$	(179.0)	$	(8.5)	$	(66.3)	$	(46.6)	$	(299.0)

The following table summarizes the amounts reclassified from accumulated other comprehensive income (loss):


(In millions)	Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)						Income Statement Location
	For the Years Ended December 31,
	2022		2021		2020
Gains (losses) on securities available for sale	$	(12.6)	$	(3.8)	$	(8.2)	Other (income) expense
	2.6		0.8		1.7		Income tax (benefit) expense

Gains (losses) on cash flow hedges	201.6		(60.0)		18.3		Revenue
	(5.5)		(0.8)		3.3		Operating expense
	(0.3)		0.2		0.3		Other (income) expense
	(19.8)		6.0		(0.1)		Income tax (benefit) expense

Gains (losses) on net investment hedges(1)	38.1		(0.6)		2.9		Other (income) expense

Currency Translation Adjustments	(58.9)		—		—		Other (income) expense

Total reclassifications, net of tax	$	145.2	$	(58.2)	$	18.2

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details

Earnings per Share

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Earnings per Share


Note 15:			Earnings per Share

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Numerator:
Net income attributable to Biogen Inc.	$	3,046.9	$	1,556.1	$	4,000.6
Denominator:
Weighted average number of common shares outstanding	145.3		149.1		160.9
Effect of dilutive securities:

Time-vested restricted stock units	0.5		0.3		0.2
Market stock units	0.1		0.1		0.1
Performance stock units settled in stock	0.1		0.1		0.1
Dilutive potential common shares	0.7		0.5		0.4
Shares used in calculating diluted earnings per share	146.0		149.6		161.3

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

Earnings per share for the years ended December 31, 2022, 2021 and 2020, reflects the repurchase of approximately 3.6 million shares, 6.0 million shares and 22.4 million shares of our common stock, respectively, under our share repurchase programs. For additional information on our share repurchase programs, please read Note 14, Equity, to these consolidated financial statements.

Share-Based Payments

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Share-Based Payments


Note 16:			Share-Based Payments

Share-Based Compensation Expense

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Research and development	$	98.5	$	89.3	$	80.0
Selling, general and administrative	175.1		169.5		131.3
Subtotal	273.6		258.8		211.3
Capitalized share-based compensation costs	(9.3)		(8.0)		(6.2)
Share-based compensation expense included in total cost and expense	264.3		250.8		205.1
Income tax effect	(49.2)		(46.7)		(33.5)
Share-based compensation expense included in net income attributable to Biogen Inc.	$	215.1	$	204.1	$	171.6

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Market stock units	$	13.2	$	45.6	$	40.5
Time-vested restricted stock units	202.3		159.8		142.6
Cash settled performance units	—		—		(1.7)
Performance units	—		—		(0.1)
Performance stock units settled in stock	35.0		23.9		7.9
Performance stock units settled in cash	10.1		12.2		8.6
Employee stock purchase plan	12.7		17.3		13.5
Stock options	0.3		—		—
Subtotal	273.6		258.8		211.3
Capitalized share-based compensation costs	(9.3)		(8.0)		(6.2)
Share-based compensation expense included in total cost and expense	$	264.3	$	250.8	$	205.1

As of December 31, 2022, unrecognized compensation cost related to unvested share-based compensation was approximately $290.5 million, net of estimated forfeitures. We expect to recognize the cost of these unvested awards over a weighted-average period of 2.0 years.

Share-Based Compensation Plans

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

Directors Plan

In May 2006 our shareholders approved the 2006 Directors Plan for share-based awards to our directors. Awards granted from the 2006 Directors Plan may include stock options, shares of restricted stock, RSUs, stock appreciation rights and other awards in such amounts and with such terms and conditions as may be determined by

a committee of our Board of Directors, subject to the provisions of the 2006 Directors Plan. We have reserved a total of 1.6 million shares of common stock for issuance under the 2006 Directors Plan. The 2006 Directors Plan provides that awards other than stock options and stock appreciation rights will be counted against the total number of shares reserved under the plan in a 1.5-to-1 ratio. In June 2015 our shareholders approved an amendment to extend the term of the 2006 Directors Plan until June 2025.

Omnibus Plan

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

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

Stock Options

During the year ended December 31, 2022, we granted approximately 81,000 stock options to our Chief Executive Officer (CEO) (2022 CEO Grant) under the 2017 Omnibus Plan with a grant date fair value of $139.10 per option for a total of approximately $11.2 million. The fair values of our stock option grants are estimated as of the date of grant using a Black-Scholes option valuation model. The estimated fair values of the stock options are then expensed over the options' vesting periods. The 2022 CEO Grant is eligible to vest in equal annual installments over a three-year period from the grant date, subject to the CEO’s continued employment. The outstanding stock options have a 10-year term and are exercisable at a price per share not less than the fair market value of the underlying common stock on the date of grant.

The total intrinsic value related to the remaining stock options previously granted in 2010 that were exercised in 2020 totaled $2.9 million.

The following table summarizes the amount of tax benefit realized for stock options and cash received from the exercise of the remaining stock options previously granted in 2010:


	For the year ended December 31,
(In millions)	2020
Tax benefit realized for stock options	$	2.9
Cash received from the exercise of stock options	0.7

Market Stock Units (MSUs)

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

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

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

Accordingly, additional MSUs may be issued or currently outstanding MSUs may be cancelled upon final determination of the number of awards earned.

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

The following table summarizes our MSU activity:


	December 31, 2022
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	257,000	$	372.08
Granted	—	—
Vested	(87,000)	369.22
Forfeited	(57,000)	371.24
Unvested at December 31, 2022	113,000	$	366.52

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

The assumptions used in our valuation are summarized as follows:


	For the Years Ended December 31,
		2021	2020
Expected dividend yield		—%	—%
Range of expected stock price volatility		54.8% - 61.6%	37.8% - 44.1%
Range of risk-free interest rates		0.06% - 0.21%	1.41% - 1.48%
30 calendar day average stock price on grant date		$262.23 - $360.31	$257.83 - $325.40
Weighted-average per share grant date fair value		$358.77	$398.61

The fair values of MSUs vested in 2022, 2021 and 2020 totaled $18.8 million, $22.5 million and $26.9 million, respectively.

Cash Settled Performance Units (CSPUs)

CSPUs awarded to employees vest in three equal annual increments beginning on the first anniversary of the grant date. The vesting of these awards is subject to the respective employee’s continued employment with such awards settled in cash. The number of CSPUs granted represents the target number of units that are eligible to be earned based on the attainment of certain performance measures established at the beginning of the performance period, which ends on December 31 of each year. Participants may ultimately earn between zero and 200.0% of the target number of units granted based on the degree of actual performance metric achievement. Accordingly, additional CSPUs may be issued or currently outstanding CSPUs may be cancelled upon final determination of the number of units earned. CSPUs are classified as liability awards and will be settled in cash based on the 30 calendar day average closing stock price through each vesting date, once the actual vested and earned number of units is known. Since no shares are issued, these awards do not dilute equity. All remaining CSPUs were fully vested as of December 31, 2020.

The cash paid in settlement of CSPUs vested in 2020 totaled $3.8 million.

Performance-vested Restricted Stock Units (PUs)

PUs are granted to certain employees in the form of RSUs that may be settled in cash or shares of our common stock at the sole discretion of the Compensation and Management Development Committee of our Board of Directors. These awards are structured and accounted for the same way as the CSPUs, and vest in three equal annual increments beginning on the first anniversary of the grant date. The number of PUs granted represents the target number of units that are eligible to be earned based on the attainment of certain performance measures established at the beginning of the performance period, which ends on December 31 of each year. Participants may ultimately earn between zero and 200.0% of the target number of units granted based on the degree of actual performance metric achievement. Accordingly, additional PUs may be issued or currently outstanding PUs may be cancelled upon final determination of the number of units earned. PUs settling in cash are based on the 30 calendar

day average closing stock price through each vesting date once the actual vested and earned number of units is known. All remaining PUs were fully vested as of December 31, 2020.

All PUs that vested in 2020 were settled in cash totaling $3.4 million.

Performance Stock Units (PSUs)

PSUs Settled in Stock

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

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

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


	December 31, 2022
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	196,000	$	289.94
Granted (1)	270,000	294.43
Vested	(44,000)	316.83
Forfeited	(86,000)	279.09
Unvested at December 31, 2022	336,000	$	292.95

(1) PSUs settled in stock granted in 2022 include awards granted in conjunction with our annual awards made in February 2022 and PSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant.

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

The assumptions used in our valuation are summarized as follows:



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

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

PSUs Settled in Cash

During the first quarter of 2018 we began granting awards for performance-vested restricted stock units that will settle in cash. PSUs awarded to employees have three performance periods and vest on the third anniversary of the grant date. The vesting of these awards is subject to the respective employee’s continued employment. The number of PSUs granted represents the target number of units that are eligible to be earned based on the

achievement of three annual performance measures established when the performance objectives are defined, which will be at the beginning of each year and will end on December 31 of such year.

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

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

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


			December 31, 2022
			Shares
Unvested at December 31, 2021			134,000
Granted (1)			24,000
Vested			(49,000)
Forfeited			(26,000)
Unvested at December 31, 2022			83,000

(1) PSUs settled in cash granted in 2022 include awards granted in conjunction with our annual awards made in February 2022 and PSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant.

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

Time-Vested Restricted Stock Units (RSUs)

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

The following table summarizes our RSU activity:


	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	1,202,000	$	291.54
Granted (1)	1,751,000	221.28
Vested	(539,000)	297.72
Forfeited	(468,000)	244.03
Unvested at December 31, 2022	1,946,000	$	237.90

(1) RSUs granted in 2022 primarily represent RSUs granted in conjunction with our annual awards made in February 2022 and awards made in conjunction with the hiring of new employees. RSUs granted in 2022 also include approximately 15,000 RSUs granted to our Board of Directors.

RSUs granted in 2021 and 2020 had weighted average grant date fair values of $276.90 and $318.87, respectively.

The fair values of RSUs vested in 2022, 2021 and 2020 totaled $116.3 million, $132.2 million and $140.5 million, respectively.

Employee Stock Purchase Plan (ESPP)

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

The following table summarizes our ESPP activity:


	For the Years Ended December 31,
(In millions, except share amounts)	2022		2021		2020
Shares issued under the 2015 ESPP	241,000		248,000		212,000
Cash received under the 2015 ESPP	$	44.2	$	54.4	$	48.6

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes


Note 17:			Income Taxes

Income Tax Expense

Income before income tax expense and the income tax expense consist of the following:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Income before income tax (benefit) expense:
Domestic	$	1,842.0	$	448.3	$	3,290.0
Foreign	1,749.8		1,296.9		1,757.5
Total income before income tax (benefit) expense	$	3,591.8	$	1,745.2	$	5,047.5
Income tax (benefit) expense:
Current:
Federal	$	694.5	$	319.1	$	647.0
State	39.0		23.1		41.2
Foreign	67.9		137.1		155.1
Total current	801.4		479.3		843.3
Deferred:
Federal	(328.3)		(242.5)		(1,749.9)
State	2.5		(11.9)		(6.8)
Foreign	157.2		(172.4)		1,905.7
Total deferred	(168.6)		(426.8)		149.0
Total income tax (benefit) expense	$	632.8	$	52.5	$	992.3

Transition Toll Tax

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

As of December 31, 2022 and 2021, we have accrued income tax liabilities of $558.0 million and $633.0 million, respectively, under the Transition Toll Tax. Of the amounts accrued as of December 31, 2022, approximately $137.8 million is expected to be paid within one year. The Transition Toll Tax will be paid in installments over an eight--year period, which started in 2018, and will not accrue interest.

Unremitted Earnings

At December 31, 2022, we considered our earnings not to be permanently reinvested outside the U.S. and therefore recorded deferred tax liabilities associated with an estimate of the total withholding taxes expected as a result of our repatriation of earnings. Other than for earnings, we are permanently reinvested for book/tax basis differences of approximately $1.5 billion as of December 31, 2022, primarily arising through the impacts of

purchase accounting. These permanently reinvested basis differences could reverse through sales of the foreign subsidiaries, as well as various other events, none of which were considered probable as of December 31, 2022. The residual U.S. tax liability, if these differences reverse, would be between $300.0 million and $400.0 million as of December 31, 2022.

TECFIDERA

Multiple TECFIDERA generic entrants are now in North America, Brazil and certain E.U. countries and have deeply discounted prices compared to TECFIDERA. The generic competition for TECFIDERA has significantly reduced our TECFIDERA revenue and we expect that TECFIDERA revenue will continue to decline in the future.

As of December 31, 2020, we assessed the realizability of our deferred tax assets that are dependent on future expected sales of TECFIDERA in the U.S. and reduced the net value of certain deferred tax assets by approximately $1.7 billion and reduced the net value of deferred tax liabilities associated with GILTI and tax credits by approximately $1.6 billion. For the year ended December 31, 2020, the income tax expense associated with these reductions was approximately $90.3 million. We continue to assess the realizability of these deferred tax assets. For the years ended December 31, 2022 and 2021, we recorded increases in these deferred tax assets of approximately $17.4 million and $108.5 million, respectively, and increases in these deferred tax liabilities of approximately $16.7 million and $103.9 million, respectively.

Deferred Tax Assets and Liabilities

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


	As of December 31,
(In millions)	2022		2021
Deferred tax assets:
Tax credits	$	112.6	$	121.0
Inventory, other reserves and accruals	202.8		199.4
Intangibles, net	1,370.3		1,477.5
Neurimmune's tax basis in ADUHELM	470.3		475.8
IRC Section 174 capitalized research and development	271.8		—
Net operating loss	1,845.9		1,973.0
Share-based compensation	37.2		31.7
Other	280.7		208.8
Valuation allowance	(2,003.3)		(1,961.3)
Total deferred tax assets	$	2,588.3	$	2,525.9
Deferred tax liabilities:
Purchased intangible assets	$	(76.1)	$	(256.6)
Samsung Bioepis investment installments	(138.0)		—
GILTI	(1,002.0)		(1,037.6)
Tax credits	(228.7)		(260.2)
Depreciation, amortization and other	(251.8)		(250.9)
Total deferred tax liabilities	$	(1,696.6)	$	(1,805.3)

The change in the valuation allowance between December 31, 2022 and 2021, was primarily related to the establishment of a valuation allowance against the deferred tax asset related to Neurimmune SubOne AG's (Neurimmune) tax basis in ADUHELM, as discussed below, and the adjustment of a valuation against certain deferred tax assets, the realization of which is dependent on future sales of TECFIDERA in the U.S., as discussed above.

In addition to deferred tax assets and liabilities, we have recorded deferred charges related to intra-entity sales of inventory. As of December 31, 2022 and 2021, the total deferred charges were $56.6 million and $39.6 million, respectively.

Inflation Reduction Act

In August 2022 the IRA was signed into law in the U.S. The IRA introduced new tax provisions, including a 15.0% corporate alternative minimum tax and a 1.0% excise tax on stock repurchases. The provisions of the IRA will be effective for periods after December 31, 2022. The enactment of the IRA did not result in any material adjustments to our income tax provision or net deferred tax assets as of December 31, 2022.

Tax Rate

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


	For the Years Ended December 31,
	2022		2021		2020
Statutory rate	21.0	%	21.0	%	21.0	%
State taxes	1.1		0.8		0.7
Taxes on foreign earnings	(4.9)		(10.5)		(3.3)
Tax credits	(1.7)		(3.8)		(1.2)
Purchased intangible assets	0.3		(1.6)		0.7
TECFIDERA impairment	—		—		1.8
GILTI	0.7		1.3		1.3
Sale of Samsung Bioepis	(1.6)		—		—
Litigation settlement agreement	2.6		—		—

Neurimmune tax impacts	2.3		(5.3)		(0.1)
Internal reorganization	(1.4)		—		—
Other	(0.8)		1.1		(1.2)
Effective tax rate	17.6	%	3.0	%	19.7	%

Changes in Tax Rate

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

For the year ended December 31, 2021, compared to 2020, the decrease in our effective tax rate, excluding the impact of the Neurimmune deferred tax asset, as discussed below, was primarily due to the change in the territorial mix of our profitability, which included the adverse effect of generic competition for TECFIDERA in the U.S. market, the tax impacts of the BIIB111 and BIIB112 impairment charges and the impact of the non-cash tax effects of changes in the value of our equity investments, where we recorded net unrealized losses in 2021 and net unrealized gains in 2020. Our 2020 effective tax rate also reflected an income tax expense related to the establishment of a valuation allowance against certain deferred tax assets, the realization of which is dependent on future sales of TECFIDERA in the U.S.

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

Neurimmune Deferred Tax Asset

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

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

For additional information on our collaboration arrangement with Neurimmune, please read Note 20, Investments in Variable Interest Entities, to these consolidated financial statements.

Tax Attributes

As of December 31, 2022, we had general business credit carry forwards for U.S. federal income tax purposes of approximately $8.1 million, which begin to expire in 2027. For U.S. state income tax purposes, we had research and investment credit carry forwards of approximately $132.7 million that begin to expire in 2023 and net operating losses of approximately $24.8 million that begin to expire in 2036. For foreign income tax purposes, we had $15.5 billion of federal net operating loss carryforwards that begin to expire in 2027 and $15.4 billion of Swiss cantonal net operating loss carryforwards that begin to expire in 2027.

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

Accounting for Uncertainty in Income Taxes

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



(In millions)	2022		2021		2020
Beginning balance	$	563.4	$	75.7	$	129.9
Additions based on tax positions related to the current period	36.3		4.2		1.5
Additions for tax positions of prior periods	23.4		509.9		51.7
Reductions for tax positions of prior periods	(14.9)		(18.8)		(63.6)
Statute expirations	(1.6)		(3.2)		(7.9)
Settlement refund (payment)	(0.2)		(4.4)		(35.9)
Ending balance	$	606.4	$	563.4	$	75.7

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

Our 2020 activity reflects the impact of the effective settlement of certain tax matters. 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 2017 or state, local or non-U.S. income tax examinations for years before 2013.

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

Included in the balance of unrecognized tax benefits as of December 31, 2022, 2021 and 2020, are $134.0 million, $87.5 million and $68.8 million (net of the federal benefit on state issues), respectively, of unrecognized tax benefits that, if recognized, would affect the effective income tax rate in future periods.

We recognize potential interest and penalties related to unrecognized tax benefits in income tax expense. During the years ended December 31, 2022, 2021 and 2020, we recognized total interest and penalty expense of $0.7 million, $2.7 million and $1.0 million, respectively. We have accrued $25.2 million and $24.8 million for the payment of interest and penalties as of December 31, 2022 and 2021, respectively.

It is reasonably possible that we will adjust the value of our uncertain tax positions related to certain transfer pricing, collaboration matters 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 $500.0 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section S99
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Other Consolidated Financial Statement Detail

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Other Consolidated Financial Statement Detail


Note 18:			Other Consolidated Financial Statement Detail

Supplemental Cash Flow Information

Supplemental disclosure of cash flow information for the years ended December 31, 2022, 2021 and 2020, is as follows:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Cash paid during the year for:
Interest	$	262.5	$	280.8	$	272.7
Income taxes	932.9		247.9		906.7

Other (Income) Expense, Net

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Gain on sale of equity interest in Samsung Bioepis(1)	$	(1,505.4)	$	—	$	—
Litigation settlement agreement and settlement fees	917.0		—		—
Interest income	(89.3)		(11.0)		(42.0)
Interest expense	246.6		253.6		222.5
(Gains) losses on investments, net	277.3		824.9		(685.7)
Foreign exchange (gains) losses, net	35.5		22.4		10.7
Other, net	10.1		5.6		(2.9)
Total other (income) expense, net	$	(108.2)	$	1,095.5	$	(497.4)

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

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

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

The following table summarizes our (gains) losses on investments, net that relates to our equity securities held as of December 31, 2022, 2021 and 2020:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Net (gains) losses recognized on equity securities	$	264.7	$	821.1	$	(693.9)
Less: Net (gains) losses realized on equity securities	—		(10.3)		(12.1)
Unrealized (gains) losses recognized on equity securities	$	264.7	$	831.4	$	(681.8)

The net unrealized losses recognized during the year ended December 31, 2022, primarily reflect a decrease in the aggregate fair value of our investments in Denali and Sangamo common stock of approximately $278.0 million. The net unrealized losses recognized during the year ended December 31, 2021, primarily reflect decreases in the aggregate fair value of our investments in Denali, Sage, Sangamo and Ionis common stock of approximately $819.6 million.

Accrued Expense and Other

Accrued expense and other consists of the following:


	As of December 31,
(In millions)	2022		2021

Revenue-related reserves for discounts and allowances	$	891.6	$	802.1
Employee compensation and benefits	395.6		345.1
Collaboration expense	277.9		324.7
Royalties and licensing fees	209.4		234.7



Other	746.9		828.6
Total accrued expense and other	$	2,521.4	$	2,535.2

Other long-term liabilities were $944.2 million and $1,320.5 million as of December 31, 2022 and 2021, respectively, and included accrued income taxes totaling $541.7 million and $664.5 million, respectively.

Collaborative and Other Relationships

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborative and Other Relationships


Note 19:			Collaborative and Other Relationships

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

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

Genentech, Inc. (Roche Group)

We have certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, CLL and other conditions; RITUXAN HYCELA for the treatment of non-Hodgkin's lymphoma and CLL; GAZYVA for the treatment of CLL and follicular lymphoma; OCREVUS for the treatment of PPMS and RMS; LUNSUMIO (mosunetuzumab), which was granted accelerated approval in the U.S. during the fourth quarter of 2022 for the treatment of relapsed or refractory follicular lymphoma; glofitamab, an investigational bispecific antibody for the potential treatment of non-Hodgkin's lymphoma; and have the option to add other potential anti-CD20 therapies, pursuant to our collaboration arrangements with Genentech, a wholly-owned member of the Roche Group. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.

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

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

RITUXAN

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

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

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

GAZYVA

The Roche Group and its sub-licensees maintain sole responsibility for the development, manufacture and commercialization of GAZYVA in the U.S. The level of gross sales of GAZYVA in the U.S. could impact 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 or GAZYVA. Genentech is solely responsible for development and commercialization of OCREVUS and funding future costs. Genentech cannot develop OCREVUS in CLL, non-Hodgkin's lymphoma or rheumatoid arthritis.

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

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

LUNSUMIO (mosunetuzumab)

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

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

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

Glofitamab

In December 2022 we entered into an agreement with Genentech related to the commercialization and sharing of economics for glofitamab, a late-stage bispecific antibody in development for B-cell non-Hodgkin's lymphoma and other blood cancers. Under the terms of this agreement, we will have no payment obligations and will receive tiered royalties on potential net sales of glofitamab in the U.S. Genentech will have sole decision-making rights on the commercialization of glofitamab within the U.S and, in the event of approval, we are eligible to receive tiered royalties in the mid-single digit range on potential net sales of glofitamab in the U.S.

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

Profit-sharing Formulas

RITUXAN and LUNSUMIO Profit Share

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




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

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

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

Our share of RITUXAN pre-tax profits in the U.S. in excess of $50.0 million for the years ended December 31, 2022, 2021 and 2020, was 37.5%.

GAZYVA Profit Share

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



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

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

Our share of GAZYVA pre-tax profits in excess of $50.0 million for the years ended December 31, 2022, 2021 and 2020, was 37.5%.

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

Revenue from Anti-CD20 Therapeutic Programs

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Royalty revenue on sales of OCREVUS	$	1,136.3	$	991.7	$	845.4
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0		647.7		1,080.2
Other revenue from anti-CD20 therapeutic programs	17.2		19.1		52.2
Total revenue from anti-CD20 therapeutic programs	$	1,700.5	$	1,658.5	$	1,977.8

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

Ionis Pharmaceuticals, Inc.

SPINRAZA

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

Under our agreement with Ionis, we make royalty payments to Ionis on annual worldwide net sales of SPINRAZA using a tiered royalty rate between 11.0% and 15.0%, which are recognized in cost of sales within our consolidated statements of income. Royalty cost of sales related to sales of SPINRAZA for the years ended December 31, 2022, 2021 and 2020, totaled approximately $243.1 million, $267.1 million and $286.6 million, respectively.

2018 Ionis Agreement

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

Upon closing, we recorded $50.9 million of the $375.0 million upfront payment as prepaid services in our consolidated balance sheets and recognized the remaining $324.1 million as research and development expense in our consolidated statements of income. The amount recorded as prepaid services represented the value of the employee resources committed to the arrangement to provide research and discovery services over the term of the agreement.

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

During the years ended December 31, 2022, 2021 and 2020, we incurred milestones of $10.0 million, $22.5 million and $11.3 million, respectively, related to the advancement of neurological targets identified under this agreement, which were recorded as research and development expense in our consolidated statements of income.

2017 SMA Collaboration Agreement

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

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

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

2013 Long-term Strategic Research Agreement

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

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

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

In December 2018 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize tofersen (BIIB067), an investigational treatment for ALS with superoxide dismutase 1 (SOD1) mutations. Potential post-licensing milestone payments may include up to $55.0 million and royalties in the low- to mid-teen percentages on potential annual worldwide net sales. We are solely responsible for the costs and expense related to the development, manufacturing and commercialization of tofersen following the option exercise.

During the years ending December 31, 2022, 2021 and 2020, we incurred milestones of $17.0 million, $10.0 million and $28.0 million, respectively, related to the advancement of programs under this agreement, which were recorded as research and development expense in our consolidated statements of income.

2012 Ionis Agreement

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

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

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

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

Eisai Co., Ltd.

LEQEMBI (lecanemab) Collaboration

We have a collaboration agreement with Eisai to jointly develop and commercialize LEQEMBI (lecanemab), an anti-amyloid antibody for the potential 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. Upon LEQEMBI marketing approval, we and Eisai will co-promote LEQEMBI and share profits and losses equally. We currently manufacture LEQEMBI drug substance and drug product and in March 2022 we extended our supply agreement with Eisai related to LEQEMBI from five years to ten years for the manufacture of LEQEMBI drug substance.

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

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

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

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

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	347.2	$	323.0	$	219.3
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our consolidated statements of income	173.6		161.5		109.6
Total sales and marketing expense incurred by the LEQEMBI Collaboration	104.6		27.2		9.8
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	52.3		13.6		4.9

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.

On March 14, 2022, we amended our ADUHELM Collaboration Agreement with Eisai. As of the amendment date, we have sole decision making and commercialization rights worldwide on ADUHELM, and beginning January 1, 2023, Eisai receives only a tiered royalty based on net sales of ADUHELM, and no longer participates in sharing ADUHELM's global profits and losses. Eisai's share of development, commercialization and manufacturing expense was limited to $335.0 million for the period from January 1, 2022 to December 31, 2022, which was achieved as of December 31, 2022. Once this limit was achieved, we became responsible for all ADUHELM related costs.

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total ADUHELM development expense	$	149.4	$	183.7	$	152.0
Biogen's share of the ADUHELM Collaboration development expense reflected in research and development expense in our consolidated statements of income	82.2		101.1		83.6
Total ADUHELM sales and marketing expense incurred by the ADUHELM Collaboration Agreement	134.2		562.3		353.0
Biogen's share of the ADUHELM Collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit (loss) sharing in our consolidated statements of income	71.5		301.4		193.7
Total ADUHELM Collaboration third party milestones	—		100.0		75.0
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit (loss) sharing in our consolidated statements of income	—		45.0		33.8

ADUHELM Co-promotion Profits and Losses

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

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

For the year ended December 31, 2020, we recognized a net reduction to our operating expense of $33.8 million to reflect Eisai's 45.0% share of the $75.0 million milestone payment made to Neurimmune related to the submission of a Biologics License Application (BLA) to the FDA for the approval of ADUHELM, which was recorded in collaboration profit (loss) sharing in our consolidated statements of income.

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

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

Amounts receivable from Eisai related to the agreements discussed above were approximately $88.0 million and $285.4 million as of December 31, 2022 and 2021, respectively. Amounts payable to Eisai related to the agreements discussed above were approximately $81.2 million and $46.5 million as of December 31, 2022 and 2021, respectively.

In addition, we and Eisai co-promote AVONEX, TYSABRI and TECFIDERA in Japan in certain settings and Eisai distributes AVONEX, TYSABRI, TECFIDERA and PLEGRIDY in India and other Asia-Pacific markets, excluding China.

UCB

In November 2003 we entered into a collaboration agreement with UCB to jointly develop and commercialize dapirolizumab pegol, an anti-CD40L pegylated Fab, for the potential treatment of systemic lupus erythematosus and other future agreed indications. Either we or UCB may propose development of dapirolizumab pegol in additional indications. If the parties do not agree to add an indication as an agreed indication to the collaboration, we or UCB may, at the sole expense of the applicable party, pursue development in such excluded indication(s), subject to an opt-in right of the non-pursuing party after proof of clinical activity.

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

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total UCB collaboration development expense	$	68.0	$	84.2	$	58.3
Biogen's share of the UCB collaboration development expense reflected in research and development expense in our consolidated statements of income	34.0		42.1		29.2

Alkermes

In November 2017 we entered into an exclusive license and collaboration agreement with Alkermes Pharma Ireland Limited, a subsidiary of Alkermes plc (Alkermes), for VUMERITY, a novel fumarate for the treatment of RMS. In October 2019 the FDA approved VUMERITY in the U.S. for the treatment of RMS. During the fourth quarter of 2021 VUMERITY was approved for the treatment of relapsing-remitting MS (RRMS) in the E.U., Switzerland and the United Kingdom (U.K.).

Under this agreement, we received an exclusive, worldwide license to develop and commercialize VUMERITY and we pay Alkermes royalties of 15.0% on worldwide net commercial sales of VUMERITY, which are recognized in cost of sales within our consolidated statements of income. Royalties payable on net commercial sales of VUMERITY are subject, under certain circumstances, to tiered minimum annual payment requirements for a period of five years following FDA approval. Royalty cost of sales related to sales of VUMERITY for the years ended December 31, 2022, 2021 and 2020, totaled approximately $83.0 million, $61.6 million and $12.9 million, respectively.

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

Alkermes currently supplies both VUMERITY and FAMPYRA to us pursuant to separate supply agreements. In October 2019 we entered into a new supply agreement and amended our license and collaboration agreement with Alkermes for VUMERITY. We have elected to initiate a technology transfer and, following a transition period, to manufacture VUMERITY or have VUMERITY manufactured by a third party we have engaged in exchange for paying an increased royalty rate to Alkermes on any portion of future worldwide net commercial sales of VUMERITY that is manufactured by us or our designee. In October 2022 we entered into a new supply agreement with Alkermes for FAMPYRA. Acorda previously supplied FAMPYRA to us pursuant to a sublicensing arrangement with Alkermes, which was terminated in October 2022 as a result of an arbitration outcome between Acorda and Alkermes.

Acorda Therapeutics, Inc.

In June 2009 we entered into a collaboration and license agreement with Acorda Therapeutics, Inc. (Acorda) to develop and commercialize products containing fampridine, such as FAMPYRA, in markets outside the U.S. We are responsible for all regulatory activities and the future clinical development of related products in those markets.

Under this agreement, we pay tiered royalties based on the level of ex-U.S. net sales and we may pay potential milestone payments based on the successful achievement of certain regulatory and commercial milestones, which would be capitalized as intangible assets upon achievement of the milestones and amortized utilizing an economic consumption model. During the third quarter of 2020 we recognized a milestone of $15.0 million, which became due

upon ex-U.S. net sales reaching $100.0 million over a period of four consecutive quarters, and was capitalized within intangible assets, net in our consolidated balance sheets.

In connection with the collaboration and license agreement, we also entered into a supply agreement with Acorda for the commercial supply of FAMPYRA. This agreement was a sublicense arrangement of an existing agreement between Acorda and Alkermes Inc., who acquired Elan Drug Technologies, the original party to the license with Acorda. In October 2022 we learned that, as a result of an arbitration filed by Acorda with the American Arbitration Association in July 2020 after Acorda and Alkermes were unable to resolve a dispute over license and supply royalties, Acorda no longer had to pay Alkermes any royalties on net sales for license and supply of FAMPYRA and Acorda was now free to use alternative sources for supply of FAMPYRA. Acorda notified us that as a result of it no longer obtaining FAMPYRA from Alkermes, that we would need to enter into a supply agreement to obtain FAMPYRA directly with Alkermes.

For the years ending December 31, 2022, 2021 and 2020, total cost of sales related to royalties and commercial supply of FAMPYRA reflected in our consolidated statements of income were approximately $46.1 million, $46.6 million and $44.5 million, respectively.

Sage Therapeutics, Inc.

In November 2020 we entered into a global collaboration and license agreement with Sage to jointly develop and commercialize zuranolone (BIIB125) 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 connection with the closing of this transaction in December 2020 we purchased $650.0 million of Sage common stock, or approximately 6.2 million shares at approximately $104.14 per share, which were initially subject to transfer restrictions. We recorded an asset in investments and other assets in our consolidated balance sheets to reflect the initial fair value of the Sage common stock acquired and a charge of approximately $209.0 million to research and development expense in our consolidated statements of income to reflect the premium paid for the Sage common stock. We also made an upfront payment of $875.0 million that was recorded as research and development expense within our consolidated statements of income for the year ended December 31, 2020.

We may also pay Sage development and commercial milestone payments that could total up to approximately $1.6 billion if all the specified milestones set forth in this collaboration are achieved. 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 may pay Sage milestones totaling $225.0 million upon the first commercial sale of zuranolone, for the potential treatment of MDD and PPD, in the U.S.

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total Sage collaboration development expense	$	173.3	$	167.7	$	—
Biogen's share of the Sage collaboration development expense reflected in research and development expense in our consolidated statements of income	86.7		83.8		—
Total Sage sales and marketing expense incurred by the collaboration	109.9		36.4		—
Biogen's share of the Sage collaboration sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	55.0		18.2		—

Denali Therapeutics Inc.

In August 2020 we entered into a collaboration and license agreement with Denali to co-develop and co-commercialize Denali's small molecule inhibitors of leucine-rich repeat kinase 2 (LRRK2) for Parkinson's disease. In addition to the LRRK2 program, we also have an exclusive option to license two preclinical programs from Denali’s Transport Vehicle platform, including its Antibody Transport Vehicle (ATV): ATV enabled anti-amyloid beta program and a second program utilizing its Transport Vehicle technology. Further, we have a right of first negotiation on two additional ATV-enabled therapeutics for indications within specific neurodegenerative diseases, should Denali decide to seek a collaboration for such programs.

As part of this collaboration we purchased $465.0 million of Denali common stock in September 2020, or approximately 13 million shares at approximately $34.94 per share, which were initially subject to transfer restrictions. We recorded an asset in investments and other assets in our consolidated balance sheets to reflect the initial fair value of the Denali common stock acquired and a charge of approximately $41.3 million to research and development expense in our consolidated statements of income to reflect the premium paid for the Denali common stock. We also made an upfront payment of $560.0 million that was recorded as research and development expense within our consolidated statements of income for the year ended December 31, 2020.

We may also pay Denali development and commercial milestone payments that could total up to approximately $1.1 billion if the milestones related to the LRRK2 program are achieved. Under this 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.

In October 2022 we and Denali announced the initiation of the Phase 3 LIGHTHOUSE study for BIIB122 (DNL151), a small molecule inhibitor of LRRK2 for the potential treatment of Parkinson's disease.

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total Denali collaboration development expense	$	75.1	$	42.5	$	14.6
Biogen's share of the Denali collaboration development expense reflected in research and development expense in our consolidated statements of income	43.8		25.5		8.8

Sangamo Therapeutics, Inc.

In February 2020 we entered into a collaboration and license agreement with Sangamo to develop and commercialize ST-501 for tauopathies, including Alzheimer's disease; ST-502 for synucleinopathies, including Parkinson’s disease; a third neuromuscular disease target; and up to nine additional neurological disease targets to be identified and selected within a five-year period. The companies are leveraging Sangamo’s proprietary zinc finger protein technology delivered via adeno-associated virus to modulate the expression of key genes involved in neurological diseases.

In connection with the closing of this transaction in April 2020 we purchased $225.0 million of Sangamo common stock, or approximately 24 million shares at approximately $9.21 per share, which were initially subject to transfer restrictions. We recorded an asset in investments and other assets in our consolidated balance sheets to reflect the initial fair value of the Sangamo common stock acquired and a charge of approximately $83.0 million to research and development expense in our consolidated statements of income to reflect the premium paid for the Sangamo common stock. We also made an upfront payment of $125.0 million that was recorded as research and development expense within our consolidated statements of income for the year ended December 31, 2020.

We may also pay Sangamo research, development, regulatory and commercial milestone payments that could total up to approximately $2.4 billion if we select all of the targets allowed under this collaboration and all the specified milestones set forth in this collaboration are achieved. Of this amount, up to $80.0 million relates to the selection of targets, $1.9 billion relates to the achievement of specified research, clinical development, regulatory and first commercial sale milestones and $380.0 million relates to the achievement of specified sales-based milestones if annual worldwide net sales of licensed products reach specified levels. In addition, we may pay Sangamo tiered royalties on potential net sales of any products developed under this collaboration in the high single digit to sub-teen percentages.

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total Sangamo collaboration development expense	$	19.1	$	22.7	$	10.1
Biogen's share of the Sangamo collaboration development expense reflected in research and development expense in our consolidated statements of income	12.1		14.6		6.4

InnoCare Pharma Limited

In July 2021 we entered into a collaboration and license agreement with InnoCare Pharma Limited (InnoCare) for orelabrutinib, an oral small molecule Bruton's tyrosine kinase inhibitor for the potential treatment of MS. Orelabrutinib is currently being studied in a multi-country, placebo-controlled Phase 2 trial in RRMS. Under the terms of this collaboration, we have exclusive rights to orelabrutinib in the field of MS worldwide and certain autoimmune diseases outside of China (including Hong Kong, Macau and Taiwan), while InnoCare retains exclusive worldwide rights to orelabrutinib in the field of oncology and certain autoimmune diseases in China (including Hong Kong, Macau and Taiwan).

In connection with the closing of this transaction in August 2021 we made an upfront payment of $125.0 million that was recorded as research and development expense within our consolidated statements of income for the year ended December 31, 2021. We may also pay InnoCare up to approximately $812.5 million in potential development milestones and potential commercial payments should this collaboration achieve certain development, commercial milestones and sales thresholds. In addition, we may pay InnoCare tiered royalties on potential net sales of any products developed under this collaboration in the low to high teen percentages.

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

Other Research and Discovery Arrangements

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

Other

For the years ended December 31, 2022, 2021 and 2020, we recorded approximately $39.2 million, $89.1 million and $92.1 million, respectively, as research and development expense in our consolidated statements of income related to other research and discovery related arrangements.

Samsung Bioepis Co., Ltd.

Joint Venture Agreement

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

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

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

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

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

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

As of December 31, 2021, the carrying value of our investment in Samsung Bioepis totaled 713.3 billion South Korean won ($599.9 million), which is classified as a component of investments and other assets within our consolidated balance sheets. In connection with the sale of Samsung Bioepis, the carrying value of our investment was reduced to zero.

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

2019 Development and Commercialization Agreement

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

In connection with this transaction, we made an upfront payment of $100.0 million to Samsung Bioepis in January 2020, of which $63.0 million was recorded as research and development expense in our consolidated statements of income in 2019 and $37.0 million was recorded as an intangible assets, net in our consolidated balance sheets in 2019.

During the third quarter of 2020 we paid Samsung Bioepis a $15.0 million development milestone, which was included in research and development expense in our consolidated statements of income. During the third quarter of 2021 we accrued $15.0 million in milestone payments related to the approval of BYOOVIZ in the U.S., the E.U. and the U.K., that were capitalized within intangible assets, net in our consolidated balance sheets. We may also pay Samsung Bioepis up to approximately $180.0 million in additional development, regulatory and sales-based milestones.

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

In December 2013 we entered into an agreement with Samsung Bioepis to commercialize, over a 10-year term, 3 anti-tumor necrosis factor (TNF) biosimilar product candidates in Europe and in the case of BENEPALI, Japan. As discussed above, we have an option to extend this agreement by an additional five years. Under this agreement, we have made upfront and clinical development milestone payments totaling $46.0 million, which were recorded as research and development expense in our consolidated statements of income as the programs they relate to had not achieved regulatory approval. We also agreed to make additional milestone payments of $25.0 million upon regulatory approval in the E.U. for each of the three anti-TNF biosimilar product candidates. IMRALDI, an adalimumab biosimilar referencing HUMIRA, FLIXABI, an infliximab biosimilar referencing REMICADE, and BENEPALI, an etanercept biosimilar referencing ENBREL, received regulatory approval in the E.U. in August 2017, May 2016 and January 2016, respectively, and we capitalized the related milestone payments totaling $75.0 million as intangible assets, net in our consolidated balance sheets.

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

We share 50.0% of the profit or loss related to our commercial agreement with Samsung Bioepis, which is recognized in collaboration profit (loss) sharing in our consolidated statements of income. For the years ended December 31, 2022, 2021 and 2020, we recognized net profit-sharing expense of $217.4 million, $285.4 million and $266.5 million, respectively, to reflect Samsung Bioepis' 50.0% sharing of the net collaboration profits.

Other Services

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

Under the 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.

For the years ended December 31, 2022, 2021 and 2020, we recognized $20.6 million, $20.7 million and $20.9 million, respectively, in royalty revenue under the license agreement, as a component of other revenue in our consolidated statements of income.

Amounts receivable from Samsung Bioepis related to the agreements discussed above were $2.0 million and $4.1 million as of December 31, 2022 and 2021, respectively. Amounts payable to Samsung Bioepis related to the agreements discussed above were $40.5 million and $148.7 million as of December 31, 2022 and 2021, respectively.

Investments in Variable Interest Entities

12 Months Ended

Dec. 31, 2022

Investments in Variable Interest Entities [Abstract]

Investments in Variable Interest Entities


Note 20:			Investments in Variable Interest Entities

Consolidated Variable Interest Entities

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

Neurimmune SubOne AG

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.

Under the terms of the Neurimmune Agreement, we were required to pay Neurimmune a milestone payment of $75.0 million upon the regulatory filing with the FDA for the approval of ADUHELM. During the second quarter of 2020 we paid Neurimmune $75.0 million upon the completed submission of the BLA for the approval of ADUHELM to the FDA, which was recognized as a charge to net income (loss) attributable to noncontrolling interests, net of tax in our consolidated statements of income. In addition, during the second quarter of 2020 we recognized net profit-sharing income of $33.8 million to reflect Eisai's 45.0% share of the $75.0 million milestone payment, which was recognized in collaboration profit (loss) sharing in our consolidated statements of income.

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

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

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

Research and development costs for which we reimburse Neurimmune are reflected in research and development expense in our consolidated statements of income. During the years ending December 31, 2022, 2021 and 2020, amounts reimbursed were immaterial.

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

Unconsolidated Variable Interest Entities

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

As of December 31, 2022 and 2021, the carrying value of our investments in certain biotechnology companies representing potential unconsolidated variable interest entities totaled $27.8 million and $24.6 million, respectively. Our maximum exposure to loss related to these variable interest entities is limited to the carrying value of our investments.

We have also entered into research collaboration agreements with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and development expense in our consolidated statements of income as they are incurred. We have provided no financing to these variable interest entities other than previous contractually required amounts.

Litigation

12 Months Ended

Dec. 31, 2022

Loss Contingency, Information about Litigation Matters [Abstract]

Litigation


Note 21:			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 these consolidated financial statements.

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

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

Loss Contingencies

ADUHELM Securities Litigation

We and certain current and former officers are named as defendants in actions filed by shareholders in November 2020 (the November 2020 Securities Action) and February 2022 (the February 2022 Securities Action) and pending in the U.S. District Court for the District of Massachusetts. The 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 September 2022, the court dismissed the November 2020 Securities Action, and the plaintiff has appealed to the U.S. Court of Appeals for the First Circuit. Our motion to dismiss the February 2022 Securities Action is pending.

Shareholder Derivative Actions

We and members of the Board of Directors are named as defendants in derivative actions filed by shareholders on February 9 and July 21, 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, breaches of fiduciary duties and waste of corporate assets, and seek declaratory and injunctive relief, monetary relief payable to Biogen, and attorneys’ fees and costs payable to the plaintiffs. The court has stayed both cases.

IMRALDI Patent Litigation

In September 2018 Fresenius Kabi Deutschland GmbH (Fresenius Kabi) commenced proceedings for damages and injunctive relief against Biogen France SAS in the Tribunal de Grande Instance de Paris and proceedings against Biogen GmbH in the Düsseldorf Regional Court, alleging that IMRALDI, the adalimumab biosimilar product of Samsung Bioepis that Biogen commercializes in Europe, infringes national counterparts of European Patent No. 3 148 510 (the EP '510 Patent). In June 2022 Fresenius Kabi amended both actions to assert claims under European Patent 3 145 488 (the EP ‘488 Patent), which expires in May 2035. No hearing has been set in either action.

In June 2022 the Technical Boards of Appeal (TBA) of the European Patent Office (EPO) affirmed the revocation of the EP '510 Patent, which resolves all pending infringement claims under the EP '510 Patent. The EPO upheld the validity of the EP '488 Patent in October 2022.

In June 2020 Fresenius Kabi commenced preliminary injunction proceedings in Denmark's Maritime and Commercial High Court alleging that IMRALDI infringes the Danish counterpart of the EP '488 Patent and a corresponding Danish utility model, DK 2020 00038 Y3. In September 2021 the Court refused Fresenius Kabi's request for a preliminary injunction and Fresenius Kabi has withdrawn its appeal.

In July 2019 Gedeon Richter Nyrt commenced proceedings for damages and injunctive relief against Biogen GmbH in the Düsseldorf Regional Court, alleging infringement of the German counterpart of European Patent No. 3 212 667 (the EP '667 Patent), which expires in October 2035. The case has been stayed pending Gedeon Richter's appeal to the TBA of the revocation of the patent. A hearing has been set by the TBA for July 2023.

In November 2020 Gedeon Richter Nyrt commenced proceedings against Biogen GmbH in the Düsseldorf Regional Court alleging infringement of a German utility model corresponding to EP '667. The proceeding has been stayed pending the outcome of proceedings that Biogen has filed in the German Patent and Trademark Office to cancel the utility model, and in which a hearing has been set for March 2023.

Dispute with Former Convergence Shareholders

In 2015 Biogen acquired Convergence, a UK company. In November and December 2019 Shareholder Representative Services LLC, on behalf of the former shareholders of Convergence, sent us correspondence asserting claims of $200.0 million for alleged breach of the contract under which we acquired Convergence. We dispute the claims.

ERISA Class Action Litigation

In September 2020 the U.S. District Court for the District of Massachusetts consolidated two cases filed against us in July and August 2020 by participants in the Biogen 401(k) Savings Plan, alleging breach of fiduciary duty under ERISA. Plaintiffs seek a declaration of the action as a class action and monetary and other relief.

Humana Patient Assistance Litigation

In September 2021 Humana Inc. (Humana) filed suit against us in the U.S. District Court for the District of Massachusetts, alleging damages related to our providing MS patients with free medications and making charitable contributions to non-profit organizations that assist MS patients. Humana alleges violation of the federal RICO Act and state laws and seeks statutory treble damages, attorneys' fees and costs. We filed a motion to dismiss, 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.

Other Matters

Government Investigations

The company has received subpoenas from the Securities and Exchange Commission seeking information relating to ADUHELM, including healthcare sites and ADUHELM's approval. In 2021 the U.S. House of Representatives Committees on Oversight and Reform and Energy (House Committees) and the Office of Inspector General (OIG) each announced investigations related to ADUHELM. In December 2022 the House Committees issued a report on their investigation.

TYSABRI Patent Matters

In September 2022 we filed an action in the U.S. District Court for the District of Delaware against Sandoz Inc. 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. No trial date has been set.

In December 2022 the TBA affirmed the revocation of our European Patent 2 676 967 (the EP '967 Patent), covering pre-treatment testing of patients using natalizumab (TYSABRI).

In September 2021 Polpharma Biologics S.A., Sandoz AG, Sandoz Limited and Sandoz GmbH filed an action in the English High Court to revoke the U.K. counterpart of the EP ‘967 Patent. No trial date has been set.

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

Pharmaceutical Works Polpharma SA (Polpharma) and Mylan Ireland Ltd. (Mylan Ireland) each filed actions in the General Court of the European Union (Polpharma in October 2018 and Mylan Ireland in November 2020) to annul the European Medicines Agency's (EMA) decision not to validate their applications to market generic versions of TECFIDERA on the grounds that TECFIDERA benefits from regulatory data protection. On May 5, 2021, the European General Court annulled the EMA's non-validation decision with respect to Polpharma. The European Court of Justice will announce its decision in our appeal of this decision on March 16, 2023. The case brought by Mylan Ireland has been stayed.

Product Liability and Other Legal Proceedings

We are also involved in product liability claims and other legal proceedings generally incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe

the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial condition.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies


Note 22:			Commitments and Contingencies

Royalty Payments

TYSABRI

In 2013 we acquired from Elan full ownership of all remaining rights to TYSABRI that we did not already own or control. Under the acquisition agreement, we are obligated to make contingent payments to Elan of 18.0% on annual worldwide net commercial sales up to $2.0 billion and 25.0% on annual worldwide net commercial sales that exceed $2.0 billion. Royalty payments to Elan and other third parties are recognized as cost of sales in our consolidated statements of income. Elan was acquired by Perrigo Company plc (Perrigo) in December 2013 and Perrigo subsequently sold its rights to these payments to a third-party effective January 2017.

SPINRAZA

In 2016 we exercised our option to develop and commercialize SPINRAZA from Ionis. Under our agreement with Ionis, we make royalty payments to Ionis on annual worldwide net commercial sales of SPINRAZA using a tiered royalty rate between 11.0% and 15.0%, which are recorded as cost of sales in our consolidated statements of income. For additional information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

VUMERITY

Under our agreement with Alkermes, we make royalty payments to Alkermes on worldwide net commercial sales of VUMERITY using a royalty rate of 15.0%, which are recorded as cost of sales in our consolidated statements of income. Royalties payable on net commercial sales of VUMERITY are subject, under certain circumstances, to tiered minimum annual payment requirements for a period of five years following FDA approval. For additional information on our collaboration arrangement with Alkermes, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Regulatory and Commercial Milestone Payments

Based on our development plans as of December 31, 2022, we could trigger potential future milestone payments to third parties of up to approximately $9.3 billion, including approximately $2.0 billion in development milestones, approximately $0.5 billion in regulatory milestones and approximately $6.8 billion in commercial milestones, as part of our various collaborations, including licensing and development programs. Payments under these agreements generally become due and payable upon achievement of certain development, regulatory or commercial milestones. Because the achievement of these milestones was not considered probable as of December 31, 2022, such contingencies have not been recorded in our financial statements. Amounts related to contingent milestone payments are not considered contractual obligations as they are contingent on the successful achievement of certain development, regulatory or commercial milestones.

If certain clinical and commercial milestones are met, we may pay up to $356.2 million in milestones in 2023 under our current agreements. This includes milestones totaling $225.0 million due to Sage upon the first commercial sale of zuranolone, for the potential treatment of MDD and PPD, in the U.S.

During the second quarter of 2020 we paid Neurimmune $75.0 million upon the completed submission of the BLA for the approval of ADUHELM to the FDA, which was recognized as a charge to net income (loss) attributable to noncontrolling interests, net of tax in our consolidated statements of income.

Other Funding Commitments

As of December 31, 2022, we have several ongoing clinical studies in various clinical trial stages. Our most significant clinical trial expenditures are to CROs. The contracts with CROs are generally cancellable, with notice, at our option. We recorded accrued expense of approximately $20.4 million in our consolidated balance sheets for expenditures incurred by CROs as of December 31, 2022. We have approximately $929.0 million in cancellable future commitments based on existing CRO contracts as of December 31, 2022.

Tax Related Obligations

We exclude liabilities pertaining to uncertain tax positions from our summary of contractual obligations as we cannot make a reliable estimate of the period of cash settlement with the respective taxing authorities. As of December 31, 2022, we have approximately $154.6 million of liabilities associated with uncertain tax positions.

As of December 31, 2022 and 2021, we have accrued income tax liabilities of approximately $558.0 million and $633.0 million, respectively, under the Transition Toll Tax. Of the amounts accrued as of December 31, 2022, approximately $137.8 million is expected to be paid within one year. The Transition Toll Tax will be paid in installments over an eight--year period, which started in 2018, and will not accrue interest. For additional information on the Transition Toll Tax, please read Note 17, Income Taxes, to these consolidated financial statements.

Guarantees

12 Months Ended

Dec. 31, 2022

Guarantees [Abstract]

Guarantees


Note 23:			Guarantees

As of December 31, 2022 and 2021, we did not have significant liabilities recorded for guarantees.

We enter into indemnification provisions under our agreements with other companies in the ordinary course of business, typically with business partners, contractors, clinical sites and customers. Under these provisions, we generally indemnify and hold harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of our activities. These indemnification provisions generally survive termination of the underlying agreement. The maximum potential amount of future payments we could be required to make under these indemnification provisions is unlimited. However, to date we have not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these agreements is minimal. Accordingly, we have no liabilities recorded for these agreements as of December 31, 2022 and 2021.

Employee Benefit Plans

12 Months Ended

Dec. 31, 2022

Retirement Benefits [Abstract]

Employee Benefit Plans


Note 24:			Employee Benefit Plans

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

401(k) Savings Plan

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

Expense related to our 401(k) Savings Plan totaled approximately $56.0 million, $58.4 million and $44.3 million for the years ended December 31, 2022, 2021 and 2020, respectively.

Deferred Compensation Plan

We maintain a non-qualified deferred compensation plan, known as the Supplemental Savings Plan (SSP), which allows a select group of management employees in the U.S. to defer a portion of their compensation. The SSP also provides certain credits to highly compensated U.S. employees that are paid by the company. These credits are known as the Restoration Match. The deferred compensation amounts are accrued when earned. Such deferred compensation is distributable in cash in accordance with the rules of the SSP. Deferred compensation amounts under such plan as of December 31, 2022 and 2021, totaled approximately $131.9 million and $131.4 million, respectively, and are included in other long-term liabilities in our consolidated balance sheets. The SSP also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement

Plan. The Restoration Match and participant contributions vest immediately. Distributions to participants can be either in one lump sum payment or annual installments as elected by the participants.

Pension Plans

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

Our Swiss plan is a government-mandated retirement fund that provides employees with a minimum investment return. The minimum investment return is determined annually by the Swiss government and was 2.00% in 2022 and 1.00% in both 2021 and 2020. Under the Swiss plan, both we and certain of our employees with annual earnings in excess of government determined amounts are required to make contributions into a fund managed by an independent investment fiduciary. Employer contributions must be in an amount at least equal to the employee’s contribution. Minimum employee contributions are based on the respective employee’s age, salary and gender. As of December 31, 2022 and 2021, the Swiss plan had an unfunded net pension obligation of $49.9 million and $64.1 million, respectively, and plan assets that totaled $193.7 million and $200.1 million, respectively. In 2022, 2021 and 2020 we recognized net expense totaling $20.0 million, $21.5 million and $15.5 million, respectively, related to our Swiss plan, of which $5.3 million, $3.5 million and $2.6 million, respectively, was included in other (income) expense, net in our consolidated statements of income.

The obligations under the German plans are unfunded and totaled $40.9 million and $68.4 million as of December 31, 2022 and 2021, respectively. Net periodic pension cost related to the German plans totaled $5.9 million, $7.6 million and $6.2 million for the years ended December 31, 2022, 2021 and 2020, respectively, of which $1.8 million, $2.1 million and $2.0 million, respectively, was included in other (income) expense, net in our consolidated statements of income.

- Definition

The entire disclosure for retirement benefits.

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+ Details

Segment Information

12 Months Ended

Dec. 31, 2022

Segment Reporting [Abstract]

Segment Information


Note 25:			Segment Information

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

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

Geographic Information

The following tables contain certain financial information by geographic area:


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

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

	December 31, 2020
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	5,900.1	$	2,495.3	$	1,161.1	$	596.7	$	539.0	$	10,692.2
Revenue from anti-CD20 therapeutic programs	1,897.4		0.1		—		—		80.3		1,977.8
Other revenue from external customers	733.6		8.0		0.1		32.9		—		774.6
Long-lived assets	1,496.3		2,290.2		31.2		16.2		10.9		3,844.8

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

Long-Lived Assets

As of December 31, 2022, 2021 and 2020, approximately $2,198.5 million, $2,237.0 million and $2,180.6 million, respectively, of our long-lived assets were related to the construction of our large-scale biologics manufacturing facility in Solothurn, Switzerland.

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8924-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 21
-Subparagraph (a)
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 280
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 32
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Subparagraph (d)
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI https://asc.fasb.org/topic&trid=2134510

+ Details

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Business Overview

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

Consolidation

Use of Estimates

Revenue Recognition

Product Revenue

Reserves for Discounts and Allowances

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

estimates. If actual results vary, we adjust these estimates, which could have an effect on earnings in the period of adjustment.

Revenue from Anti-CD20 Therapeutic Programs

Revenue from anti-CD20 therapeutic programs consist of:

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

(ii) royalty revenue on sales of OCREVUS; and

(ii) other revenue from anti-CD20 therapeutic programs, which consists of our share of pre-tax co-promotion profits on RITUXAN in Canada.

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

Other Revenue

Contract Manufacturing and Other Revenue

Royalty Revenue

Collaborative and Other Relationships

Fair Value Measurements

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

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

Other Assets and Liabilities

Cash and Cash Equivalents

Accounts Receivable

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

Receivables from Samsung BioLogics

Concentration of Credit Risk

Marketable Securities and Other Investments

Marketable Debt Securities

Marketable Equity Securities and Venture Capital Funds

Non-Marketable Equity Securities

Evaluating Marketable Debt Securities for Other-than-Temporary Impairments

Equity Method of Accounting

Equity Method of AccountingIn circumstances where we have the ability to exercise significant influence over the operating and financial policies of a company in which we have an investment, we utilize the equity method of accounting for recording investment activity. In assessing whether we exercise significant influence, we consider the nature and magnitude of our investment, the voting and protective rights we hold, any participation in the governance of the other company and other relevant factors such as the presence of a collaborative or other business relationship. Under the equity method of accounting, we record in our consolidated statements of income our share of income or loss of the other company. If our share of losses exceeds the carrying value of our investment, we will suspend recognizing additional losses and will continue to do so unless we commit to providing additional funding.

Inventory

Capitalization of Inventory Costs

Obsolescence and Unmarketable Inventory

Property, Plant and Equipment


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

Leases

Intangible Assets

Acquired In-process Research and Development (IPR&D)

Goodwill

Impairment of Long-Lived Assets

Contingent Consideration

commercialization, changes in the assumed achievement or timing of any cumulative sales-based and development milestones, changes in the probability of certain clinical events and changes in the assumed probability associated with regulatory approval. Discount rates in our valuation models represent a measure of the credit risk associated with settling the liability. The period over which we discount our contingent obligations is based on the current development stage of the product candidates, our specific development plan for that product candidate adjusted for the probability of completing the development step and when the contingent payments would be triggered. In estimating the probability of success, we utilize data regarding similar milestone events from several sources, including industry studies and our own experience. These fair value measurements are based on significant inputs not observable in the market. Significant judgment is employed in determining the appropriateness of these assumptions as of the acquisition date and for each subsequent period.

Derivative Instruments and Hedging Activities

Cash Flow and Fair Value Derivative Instruments

Net Investment Derivative Instruments

For additional information on our derivative instruments and hedging activities, please read Note 10, Derivative Instruments, to these consolidated financial statements.

Translation of Foreign Currencies

Royalty Cost of Sales

Royalty Cost of SalesWe make royalty payments to a number of third-parties under license or purchase agreements associated with our acquisition of intellectual property. These royalty payments are typically calculated as a percentage (royalty rate) of the sales of our products in a particular year. That royalty rate may remain constant, increase or decrease within each year based on the total amount of sales during the annual period. Each quarterly period, we estimate our total royalty obligation for the full year and recognize the proportional amount as cost of sales based on actual quarterly sales as a percentage of full year estimated sales. For example, if the level of net sales in any calendar year increases the royalty rate within the year, we will record our cost of sales at an even rate over the year, based on the estimated blended royalty rate.

Accounting for Share-Based Compensation

The fair values of our RSUs are based on the market value of our stock on the date of grant. Compensation expense for RSUs is recognized straight-line over the applicable service period.

Research and Development Expense

Selling, General and Administrative Expense

Advertising costs are expensed as incurred.

Income Taxes

Contingencies

Earnings per Share

New Accounting Pronouncements

Fair Value Measurements

Income Taxes

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Property, plant and equipment estimated useful lives


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

Restructuring (Tables)

12 Months Ended

Dec. 31, 2022

Restructuring and Related Activities [Abstract]

Schedule of Restructuring Reserve by Type of Cost

The following table summarizes the charges and spending related to our 2022 workforce reductions for the year ended December 31, 2022:


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

Revenue (Tables)

12 Months Ended

Dec. 31, 2022

Revenue from Contract with Customer [Abstract]

Revenue by product

Revenue by product are summarized as follows:


	For the Years Ended December 31,
	2022						2021						2020
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis (MS):
TECFIDERA	$	417.7	$	1,026.2	$	1,443.9	$	680.6	$	1,271.3	$	1,951.9	$	2,677.7	$	1,163.4	$	3,841.1
VUMERITY(1)	521.3		32.1		553.4		408.9		1.5		410.4		64.3		—		64.3
Total Fumarate	939.0		1,058.3		1,997.3		1,089.5		1,272.8		2,362.3		2,742.0		1,163.4		3,905.4
AVONEX	649.2		324.3		973.5		830.2		378.5		1,208.7		1,083.4		408.5		1,491.9
PLEGRIDY	148.4		183.5		331.9		152.9		204.5		357.4		190.1		195.5		385.6
Total Interferon	797.6		507.8		1,305.4		983.1		583.0		1,566.1		1,273.5		604.0		1,877.5
TYSABRI	1,123.4		907.5		2,030.9		1,142.2		920.9		2,063.1		1,096.8		849.3		1,946.1
FAMPYRA	—		96.6		96.6		—		105.2		105.2		—		103.1		103.1
Subtotal: MS	2,860.0		2,570.2		5,430.2		3,214.8		2,881.9		6,096.7		5,112.3		2,719.8		7,832.1

Spinal Muscular Atrophy:
SPINRAZA	600.2		1,193.3		1,793.5		587.9		1,317.2		1,905.1		787.8		1,264.3		2,052.1

Biosimilars:
BENEPALI	—		441.0		441.0		—		498.3		498.3		—		481.6		481.6
IMRALDI	—		224.5		224.5		—		233.4		233.4		—		216.3		216.3
FLIXABI	—		81.3		81.3		—		99.4		99.4		—		97.9		97.9
BYOOVIZ(2)	4.3		—		4.3		—		—		—		—		—		—
Subtotal: Biosimilars	4.3		746.8		751.1		—		831.1		831.1		—		795.8		795.8

Other:
FUMADERM	—		8.2		8.2		—		11.0		11.0		—		12.2		12.2
ADUHELM	4.8		—		4.8		3.0		—		3.0		—		—		—
Total product revenue	$	3,469.3	$	4,518.5	$	7,987.8	$	3,805.7	$	5,041.2	$	8,846.9	$	5,900.1	$	4,792.1	$	10,692.2

(1) VUMERITY became commercially available in the E.U. during the fourth quarter of 2021.

(2) BYOOVIZ launched in the U.S. in June 2022 and became commercially available during the third quarter of 2022.

Analysis of change in reserves

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


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


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


	December 31, 2020
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Beginning balance	$	131.1	$	1,027.3	$	40.5	$	1,198.9
Current provisions relating to sales in current year	774.7		3,308.8		19.0		4,102.5
Adjustments relating to prior years	(1.0)		(54.0)		1.3		(53.7)
Payments/credits relating to sales in current year	(635.1)		(2,426.1)		—		(3,061.2)
Payments/credits relating to sales in prior years	(128.3)		(763.0)		(19.2)		(910.5)
Ending balance	$	141.4	$	1,093.0	$	41.6	$	1,276.0

Total reserves included in consolidated balance sheet

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


	As of December 31,
(In millions)	2022		2021
Reduction of accounts receivable	$	143.4	$	133.2
Component of accrued expense and other	891.6		802.1
Total revenue-related reserves	$	1,035.0	$	935.3

Revenues from anti-CD20 therapeutic programs

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Royalty revenue on sales of OCREVUS	$	1,136.3	$	991.7	$	845.4
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0		647.7		1,080.2
Other revenue from anti-CD20 therapeutic programs	17.2		19.1		52.2
Total revenue from anti-CD20 therapeutic programs	$	1,700.5	$	1,658.5	$	1,977.8

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Royalty revenue on sales of OCREVUS	$	1,136.3	$	991.7	$	845.4
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0		647.7		1,080.2
Other revenue from anti-CD20 therapeutic programs	17.2		19.1		52.2
Total revenue from anti-CD20 therapeutic programs	$	1,700.5	$	1,658.5	$	1,977.8

Other revenues

Other revenue consists of royalty revenue and contract manufacturing and other revenue and is summarized as follows:


	For the Years Ended December 31,
(In millions)	2022		2021		2020




Contract manufacturing and other revenue	$	417.7	$	427.7	$	719.1
Royalty revenue	67.4		48.6		55.5
Total other revenue	$	485.1	$	476.3	$	774.6

Inventory (Tables)

12 Months Ended

Dec. 31, 2022

Inventory Disclosure [Abstract]

Components of inventory

The components of inventory are summarized as follows:


	As of December 31,
(In millions)	2022		2021
Raw materials	$	413.2	$	349.6
Work in process(1)	751.9		814.0
Finished goods	200.4		187.9
Total inventory	$	1,365.5	$	1,351.5

Balance Sheet Classification:
Inventory	$	1,344.4	$	1,351.5
Investments and other assets	21.1		—
Total inventory	$	1,365.5	$	1,351.5

(1) Work in process inventory as of December 31, 2022, includes approximately $89.8 million related to LEQEMBI.

Intangible Assets and Goodwill (Tables)

12 Months Ended

Dec. 31, 2022

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets

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


		As of December 31, 2022						As of December 31, 2021
(In millions)	Estimated Life	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Completed technology	4-28 years	$	7,415.3	$	(5,629.2)	$	1,786.1	$	7,413.1	$	(5,388.5)	$	2,024.6
In-process research and development	Indefinite until commercialization	—		—		—		132.7		—		132.7
Trademarks and trade names	Indefinite	64.0		—		64.0		64.0		—		64.0
Total intangible assets		$	7,479.3	$	(5,629.2)	$	1,850.1	$	7,609.8	$	(5,388.5)	$	2,221.3

Estimated future amortization of intangible assets

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


(In millions)	As of December 31, 2022
2023	$	215.0
2024	195.0
2025	190.0
2026	175.0
2027	165.0

Summary of roll forward of the changes in goodwill

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


	As of December 31,
(In millions)	2022		2021
Goodwill, beginning of year	$	5,761.1	$	5,762.1


Other	(12.1)		(1.0)
Goodwill, end of year	$	5,749.0	$	5,761.1

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
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Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1A
-URI https://asc.fasb.org/extlink&oid=121556970&loc=SL108378252-109267

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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-Paragraph 1
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Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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-Section 50
-Paragraph 1
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
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-URI https://asc.fasb.org/extlink&oid=121556970&loc=d3e13854-109267

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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-Section 55
-Paragraph 24
-URI https://asc.fasb.org/extlink&oid=122137925&loc=d3e14258-109268

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267

+ Details

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Summary of assets and liabilities recorded at fair value


	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	$	—


	As of December 31, 2021
(In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	1,632.2	$	—	$	1,632.2	$	—
Marketable debt securities:
Corporate debt securities	1,108.2		—		1,108.2		—
Government securities	1,192.7		—		1,192.7		—
Mortgage and other asset backed securities	132.2		—		132.2		—
Marketable equity securities	1,048.5		181.7		866.8		—
Derivative contracts	80.9		—		80.9		—
Plan assets for deferred compensation	33.4		—		33.4		—
Total	$	5,228.1	$	181.7	$	5,046.4	$	—
Liabilities:
Derivative contracts	$	10.8	$	—	$	10.8	$	—
Contingent consideration obligations	209.1		—		—		209.1
Total	$	219.9	$	—	$	10.8	$	209.1

Summary of significant unobservable inputs


	Quantitative Information about Level 3 Fair Value Measurements
	Fair Value					Significant Unobservable Input(s)	Range	Weighted Average
(In millions)	2022(1)		2021		Valuation Technique		2021	2022(1)		2021




Liabilities:
Contingent consideration obligations	$	—	$	209.1	Discounted cash flow	Discount rate	1.30%	—	%	1.30	%
						Expected timing of achievement of development milestones	2023 to 2027	—		—

(1) During the year ended December 31, 2022, we discontinued the development of vixotrigine and as a result we adjusted the fair value of our contingent consideration obligations to zero.

Summary of fair and carrying value of debt instruments

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


	Fair Value As of December 31,
(In millions)	2022		2021
3.625% Senior Notes due September 15, 2022(1)	$	—	$	1,020.0
4.050% Senior Notes due September 15, 2025	1,699.9		1,895.2
2.250% Senior Notes due May 1, 2030	1,219.0		1,475.9
5.200% Senior Notes due September 15, 2045	1,033.2		1,463.0
3.150% Senior Notes due May 1, 2050	989.0		1,457.7
3.250% Senior Notes due February 15, 2051	469.1		692.9
Total	$	5,410.2	$	8,004.7

Fair value of contingent consideration obligations

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


	As of December 31,
(In millions)	2022		2021
Fair value, beginning of year	$	209.1	$	259.8
Changes in fair value	(209.1)		(50.7)

Fair value, end of year	$	—	$	209.1

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2022

Investments, All Other Investments [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 three months from the date of purchase included in cash and cash equivalents in our consolidated balance sheets:


	As of December 31,
(In millions)	2022		2021
Commercial paper	$	177.2	$	247.6
Overnight reverse repurchase agreements	59.0		200.0
Money market funds	2,581.5		901.6
Short-term debt securities	29.9		283.0
Total	$	2,847.6	$	1,632.2

Marketable debt and equity securities

The following tables summarize our marketable debt and equity securities, classified as available for sale:


	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, current	$	1,133.8	$	—	$	(342.7)	$	791.1

Total marketable equity securities	$	1,133.8	$	—	$	(342.7)	$	791.1


	As of December 31, 2021
(In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable debt securities:
Corporate debt securities:
Current	$	723.6	$	0.1	$	(0.3)	$	723.4
Non-current	385.4		0.2		(0.8)		384.8
Government securities:
Current	817.0		—		(0.4)		816.6
Non-current	377.0		0.1		(1.0)		376.1
Mortgage and other asset backed securities:
Current	1.1		—		—		1.1
Non-current	131.8		—		(0.7)		131.1
Total marketable debt securities	$	2,435.9	$	0.4	$	(3.2)	$	2,433.1

Marketable equity securities:
Marketable equity securities, current	$	33.9	$	9.9	$	—	$	43.8
Marketable equity securities, non-current	1,133.1		151.0		(279.4)		1,004.7
Total marketable equity securities	$	1,167.0	$	160.9	$	(279.4)	$	1,048.5

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				2021
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	1,473.5	$	1,483.3	$	1,541.1	$	1,541.7
Due after one year through five years	694.4		703.7		868.2		870.2
Due after five years	11.3		12.1		23.8		24.0
Total marketable debt securities	$	2,179.2	$	2,199.1	$	2,433.1	$	2,435.9

Proceeds from marketable securities, excluding strategic investments

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Proceeds from maturities and sales	$	3,671.0	$	3,405.4	$	7,299.4
Realized gains	—		0.2		17.7
Realized losses	12.6		4.0		26.0

Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2022

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Foreign currency forward contracts that were entered into to hedge forecasted revenue

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


	Notional Amount As of December 31,
(In millions)	2022		2021
Euro	$	1,495.5	$	1,828.0
British pound	162.8		166.2

Japanese yen	—		72.7
Canadian dollar	57.2		59.9
Total foreign currency forward contracts	$	1,715.5	$	2,126.8

Summary of unrealized gain (loss) on derivative instruments that are included in AOCI


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Unrealized gains	$	29.9	$	60.8	$	—
Unrealized (losses)	(21.3)		(7.0)		(212.5)
Net unrealized gains (losses)	$	8.6	$	53.8	$	(212.5)

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

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


For the Years Ended December 31,
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)							Net Gains/(Losses) Recognized in Operating Income (in millions)
Location	2022		2021		2020		Location	2022		2021		2020
Revenue	$	201.6	$	(60.0)	$	18.3	Revenue	$	(8.6)	$	(8.4)	$	(9.9)
Operating expense	(5.5)		(0.8)		3.3		Operating expense	—		—		—

Summary of the effect of derivatives designated as net investment hedging instruments on our consolidated statement of income

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


For the Years Ended December 31,
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion) (in millions)							Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions)							Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)
Location	2022		2021		2020		Location	2022		2021		2020		Location	2022		2021		2020
Gains (losses) on net investment hedge(1)	$	20.4	$	46.0	$	(35.1)	Gains (losses) on net investment hedge(1)	$	(3.2)	$	(3.2)	$	4.5	Other (income) expense(1)	$	(4.6)	$	(0.6)	$	2.9

Summary of the fair value for our outstanding derivatives

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


		As of December 31,
(In millions)	Balance Sheet Location	2022		2021
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	37.9	$	66.2
	Investments and other assets	—		5.5
Liability derivative instruments	Accrued expense and other	18.4		6.6


Net Investment Hedging Instruments:(1)
Asset derivative instruments	Other current assets	—		4.1






Other Derivative Instruments:
Asset derivative instruments	Other current assets	25.1		5.1
Liability derivative instruments	Accrued expense and other	7.6		4.2

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Components of property, plant and equipment, net

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


	As of December 31,
(In millions)	2022		2021
Land	$	202.4	$	207.5
Buildings	1,592.9		1,699.7
Leasehold improvements	107.7		121.0
Machinery and equipment	1,611.5		1,585.5
Computer software and hardware	999.9		971.6
Furniture and fixtures	61.1		67.4
Construction in progress	888.8		770.3
Total cost	5,464.3		5,423.0
Less: accumulated depreciation	(2,165.7)		(2,006.6)
Total property, plant and equipment, net	$	3,298.6	$	3,416.4

Leases (Tables)

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Schedule of operating leases

All of our leases qualify as operating leases. The following table summarizes the presentation in our consolidated balance sheets of our operating leases:


		As of December 31,
(In millions)	Balance sheet location	2022		2021
Assets:
Operating lease assets	Operating lease assets	$	403.9	$	375.4

Liabilities
Current operating lease liabilities	Accrued expense and other	$	97.2	$	89.1
Non-current operating lease liabilities	Long-term operating lease liabilities	333.0		330.4
Total operating lease liabilities		$	430.2	$	419.5

Operating lease costs

The following table summarizes the effect of lease costs in our consolidated statements of income:


		For the Years Ended December 31,
(In millions)	Income Statement Location	2022		2021		2020
Operating lease cost	Research and development	$	2.0	$	3.4	$	5.2
	Selling, general and administrative	95.9		95.9		93.1
Variable lease cost	Research and development	0.4		0.8		1.1
	Selling, general and administrative	25.4		25.7		21.1
Sublease income	Selling, general and administrative	(24.0)		(23.9)		(24.2)
	Other (income) expense, net	(4.1)		(4.0)		(3.9)
Net lease cost		$	95.6	$	97.9	$	92.4

Operating lease liability maturity

The minimum lease payments for the next five years and thereafter is expected to be as follows:


(In millions)	As of December 31, 2022
2023	$	111.0
2024	107.0
2025	80.5
2026	65.7
2027	69.5
Thereafter	36.6
Total lease payments	$	470.3
Less: interest	40.1
Present value of operating lease liabilities	$	430.2

Operating lease weighted average remaining term and discount rate

The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows:


	As of December 31,
	2022		2021
Weighted average remaining lease term in years	4.64		5.43
Weighted average discount rate	3.7	%	2.9	%

Operating lease supplemental cash flow disclosure

Supplemental disclosure of cash flow information related to our operating leases included in cash flow provided by operating activities in our consolidated statements of cash flow is as follows:


	As of December 31,
(In millions)	2022		2021		2020
Cash paid for amounts included in the measurement of lease liabilities	$	107.4	$	105.8	$	100.2
Operating lease assets obtained in exchange for lease obligations	108.3		18.1		59.0

Indebtedness (Tables)

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Summary of indebtedness

Our indebtedness is summarized as follows:


	As of December 31,
(In millions)	2022		2021
Current portion:
3.625% Senior Notes due September 15, 2022(1)	$	—	$	999.1
Current portion of notes payable	$	—	$	999.1
Non-current portion:
4.050% Senior Notes due September 15, 2025	$	1,744.7	$	1,742.9
2.250% Senior Notes due May 1, 2030	1,492.9		1,492.0
5.200% Senior Notes due September 15, 2045	1,100.3		1,099.9
3.150% Senior Notes due May 1, 2050	1,473.8		1,473.2
3.250% Senior Notes due February 15, 2051	469.3		466.0
Non-current portion of notes payable	$	6,281.0	$	6,274.0

(1) Our 3.625% Senior Notes due September 15, 2022, were redeemed in full in July 2022.

Total debt maturities

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


(In millions)	As of December 31, 2022
2023	$	—
2024	—
2025	1,750.0
2026	—
2027	—
2028 and thereafter	4,817.3
Total debt	$	6,567.3
Less: debt discount and issuance fees	(286.3)
Total long-term debt	$	6,281.0

Equity (Tables)

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Summary of common stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2022, 2021 and 2020:

As of December 31, 2022

As of December 31, 2021

As of December 31, 2020

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

167.9

144.0

1,000.0

170.8

147.0

1,000.0

176.2

152.4

Schedule of Accumulated Other Comprehensive Income (Loss)

The following tables summarize the changes in accumulated other comprehensive income (loss), net of tax by component:


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


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


	December 31, 2020
(In millions)	Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax		Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax		Gains (Losses) on Net Investment Hedges, Net of Tax		Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax		Currency Translation Adjustments		Total
Balance, December 31, 2019	$	4.2	$	7.8	$	25.1	$	(32.8)	$	(139.5)	$	(135.2)
Other comprehensive income (loss) before reclassifications	(9.3)		(165.0)		(30.7)		(33.5)		92.9		(145.6)
Amounts reclassified from accumulated other comprehensive income (loss)	6.5		(21.8)		(2.9)		—		—		(18.2)
Net current period other comprehensive income (loss)	(2.8)		(186.8)		(33.6)		(33.5)		92.9		(163.8)
Balance, December 31, 2020	$	1.4	$	(179.0)	$	(8.5)	$	(66.3)	$	(46.6)	$	(299.0)

Reclassification out of Accumulated Other Comprehensive Income

The following table summarizes the amounts reclassified from accumulated other comprehensive income (loss):


(In millions)	Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)						Income Statement Location
	For the Years Ended December 31,
	2022		2021		2020
Gains (losses) on securities available for sale	$	(12.6)	$	(3.8)	$	(8.2)	Other (income) expense
	2.6		0.8		1.7		Income tax (benefit) expense

Gains (losses) on cash flow hedges	201.6		(60.0)		18.3		Revenue
	(5.5)		(0.8)		3.3		Operating expense
	(0.3)		0.2		0.3		Other (income) expense
	(19.8)		6.0		(0.1)		Income tax (benefit) expense

Gains (losses) on net investment hedges(1)	38.1		(0.6)		2.9		Other (income) expense

Currency Translation Adjustments	(58.9)		—		—		Other (income) expense

Total reclassifications, net of tax	$	145.2	$	(58.2)	$	18.2

(1)

Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Basic and diluted earnings per share

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Numerator:
Net income attributable to Biogen Inc.	$	3,046.9	$	1,556.1	$	4,000.6
Denominator:
Weighted average number of common shares outstanding	145.3		149.1		160.9
Effect of dilutive securities:

Time-vested restricted stock units	0.5		0.3		0.2
Market stock units	0.1		0.1		0.1
Performance stock units settled in stock	0.1		0.1		0.1
Dilutive potential common shares	0.7		0.5		0.4
Shares used in calculating diluted earnings per share	146.0		149.6		161.3

Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Share-based compensation expense included in consolidated statements of income

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Research and development	$	98.5	$	89.3	$	80.0
Selling, general and administrative	175.1		169.5		131.3
Subtotal	273.6		258.8		211.3
Capitalized share-based compensation costs	(9.3)		(8.0)		(6.2)
Share-based compensation expense included in total cost and expense	264.3		250.8		205.1
Income tax effect	(49.2)		(46.7)		(33.5)
Share-based compensation expense included in net income attributable to Biogen Inc.	$	215.1	$	204.1	$	171.6

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

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Market stock units	$	13.2	$	45.6	$	40.5
Time-vested restricted stock units	202.3		159.8		142.6
Cash settled performance units	—		—		(1.7)
Performance units	—		—		(0.1)
Performance stock units settled in stock	35.0		23.9		7.9
Performance stock units settled in cash	10.1		12.2		8.6
Employee stock purchase plan	12.7		17.3		13.5
Stock options	0.3		—		—
Subtotal	273.6		258.8		211.3
Capitalized share-based compensation costs	(9.3)		(8.0)		(6.2)
Share-based compensation expense included in total cost and expense	$	264.3	$	250.8	$	205.1

Tax benefit and cash received from stock option exercises

The following table summarizes the amount of tax benefit realized for stock options and cash received from the exercise of the remaining stock options previously granted in 2010:


	For the year ended December 31,
(In millions)	2020
Tax benefit realized for stock options	$	2.9
Cash received from the exercise of stock options	0.7

Summary of market stock unit activity

The following table summarizes our MSU activity:


	December 31, 2022
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	257,000	$	372.08
Granted	—	—
Vested	(87,000)	369.22
Forfeited	(57,000)	371.24
Unvested at December 31, 2022	113,000	$	366.52

Assumptions used in valuation of market based stock units

The assumptions used in our valuation are summarized as follows:


	For the Years Ended December 31,
		2021	2020
Expected dividend yield		—%	—%
Range of expected stock price volatility		54.8% - 61.6%	37.8% - 44.1%
Range of risk-free interest rates		0.06% - 0.21%	1.41% - 1.48%
30 calendar day average stock price on grant date		$262.23 - $360.31	$257.83 - $325.40
Weighted-average per share grant date fair value		$358.77	$398.61

The assumptions used in our valuation are summarized as follows:



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

Performance stock units settled in stock activity

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


	December 31, 2022
	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	196,000	$	289.94
Granted (1)	270,000	294.43
Vested	(44,000)	316.83
Forfeited	(86,000)	279.09
Unvested at December 31, 2022	336,000	$	292.95

Performance stock units settled in cash activity

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


			December 31, 2022
			Shares
Unvested at December 31, 2021			134,000
Granted (1)			24,000
Vested			(49,000)
Forfeited			(26,000)
Unvested at December 31, 2022			83,000

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

Time-vested restricted stock units activity

The following table summarizes our RSU activity:


	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	1,202,000	$	291.54
Granted (1)	1,751,000	221.28
Vested	(539,000)	297.72
Forfeited	(468,000)	244.03
Unvested at December 31, 2022	1,946,000	$	237.90

Shares issued under employee stock purchase plan

The following table summarizes our ESPP activity:


	For the Years Ended December 31,
(In millions, except share amounts)	2022		2021		2020
Shares issued under the 2015 ESPP	241,000		248,000		212,000
Cash received under the 2015 ESPP	$	44.2	$	54.4	$	48.6

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income before income tax provision and the income tax expense

Income before income tax expense and the income tax expense consist of the following:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Income before income tax (benefit) expense:
Domestic	$	1,842.0	$	448.3	$	3,290.0
Foreign	1,749.8		1,296.9		1,757.5
Total income before income tax (benefit) expense	$	3,591.8	$	1,745.2	$	5,047.5
Income tax (benefit) expense:
Current:
Federal	$	694.5	$	319.1	$	647.0
State	39.0		23.1		41.2
Foreign	67.9		137.1		155.1
Total current	801.4		479.3		843.3
Deferred:
Federal	(328.3)		(242.5)		(1,749.9)
State	2.5		(11.9)		(6.8)
Foreign	157.2		(172.4)		1,905.7
Total deferred	(168.6)		(426.8)		149.0
Total income tax (benefit) expense	$	632.8	$	52.5	$	992.3

Components of deferred tax assets and liabilities

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


	As of December 31,
(In millions)	2022		2021
Deferred tax assets:
Tax credits	$	112.6	$	121.0
Inventory, other reserves and accruals	202.8		199.4
Intangibles, net	1,370.3		1,477.5
Neurimmune's tax basis in ADUHELM	470.3		475.8
IRC Section 174 capitalized research and development	271.8		—
Net operating loss	1,845.9		1,973.0
Share-based compensation	37.2		31.7
Other	280.7		208.8
Valuation allowance	(2,003.3)		(1,961.3)
Total deferred tax assets	$	2,588.3	$	2,525.9
Deferred tax liabilities:
Purchased intangible assets	$	(76.1)	$	(256.6)
Samsung Bioepis investment installments	(138.0)		—
GILTI	(1,002.0)		(1,037.6)
Tax credits	(228.7)		(260.2)
Depreciation, amortization and other	(251.8)		(250.9)
Total deferred tax liabilities	$	(1,696.6)	$	(1,805.3)

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

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


	For the Years Ended December 31,
	2022		2021		2020
Statutory rate	21.0	%	21.0	%	21.0	%
State taxes	1.1		0.8		0.7
Taxes on foreign earnings	(4.9)		(10.5)		(3.3)
Tax credits	(1.7)		(3.8)		(1.2)
Purchased intangible assets	0.3		(1.6)		0.7
TECFIDERA impairment	—		—		1.8
GILTI	0.7		1.3		1.3
Sale of Samsung Bioepis	(1.6)		—		—
Litigation settlement agreement	2.6		—		—

Neurimmune tax impacts	2.3		(5.3)		(0.1)
Internal reorganization	(1.4)		—		—
Other	(0.8)		1.1		(1.2)
Effective tax rate	17.6	%	3.0	%	19.7	%

Reconciliation of beginning and ending amount of unrecognized tax benefits

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



(In millions)	2022		2021		2020
Beginning balance	$	563.4	$	75.7	$	129.9
Additions based on tax positions related to the current period	36.3		4.2		1.5
Additions for tax positions of prior periods	23.4		509.9		51.7
Reductions for tax positions of prior periods	(14.9)		(18.8)		(63.6)
Statute expirations	(1.6)		(3.2)		(7.9)
Settlement refund (payment)	(0.2)		(4.4)		(35.9)
Ending balance	$	606.4	$	563.4	$	75.7

Other Consolidated Financial Statement Detail (Tables)

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Supplemental cash flow information

Supplemental disclosure of cash flow information for the years ended December 31, 2022, 2021 and 2020, is as follows:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Cash paid during the year for:
Interest	$	262.5	$	280.8	$	272.7
Income taxes	932.9		247.9		906.7

Other income (expense), net

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Gain on sale of equity interest in Samsung Bioepis(1)	$	(1,505.4)	$	—	$	—
Litigation settlement agreement and settlement fees	917.0		—		—
Interest income	(89.3)		(11.0)		(42.0)
Interest expense	246.6		253.6		222.5
(Gains) losses on investments, net	277.3		824.9		(685.7)
Foreign exchange (gains) losses, net	35.5		22.4		10.7
Other, net	10.1		5.6		(2.9)
Total other (income) expense, net	$	(108.2)	$	1,095.5	$	(497.4)

Gain (loss) on investments

The following table summarizes our (gains) losses on investments, net that relates to our equity securities held as of December 31, 2022, 2021 and 2020:


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Net (gains) losses recognized on equity securities	$	264.7	$	821.1	$	(693.9)
Less: Net (gains) losses realized on equity securities	—		(10.3)		(12.1)
Unrealized (gains) losses recognized on equity securities	$	264.7	$	831.4	$	(681.8)

Accrued expense and other

Accrued expense and other consists of the following:


	As of December 31,
(In millions)	2022		2021

Revenue-related reserves for discounts and allowances	$	891.6	$	802.1
Employee compensation and benefits	395.6		345.1
Collaboration expense	277.9		324.7
Royalties and licensing fees	209.4		234.7



Other	746.9		828.6
Total accrued expense and other	$	2,521.4	$	2,535.2

Collaborative and Other Relationships (Tables)

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Co-promotion profit sharing formula

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




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

Pretax profit sharing formula

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



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

Revenues from anti-CD20 therapeutic programs

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Royalty revenue on sales of OCREVUS	$	1,136.3	$	991.7	$	845.4
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0		647.7		1,080.2
Other revenue from anti-CD20 therapeutic programs	17.2		19.1		52.2
Total revenue from anti-CD20 therapeutic programs	$	1,700.5	$	1,658.5	$	1,977.8

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Royalty revenue on sales of OCREVUS	$	1,136.3	$	991.7	$	845.4
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0		647.7		1,080.2
Other revenue from anti-CD20 therapeutic programs	17.2		19.1		52.2
Total revenue from anti-CD20 therapeutic programs	$	1,700.5	$	1,658.5	$	1,977.8

Summary of activity related to BAN2401 and Elenbecestat collaboration

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	347.2	$	323.0	$	219.3
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our consolidated statements of income	173.6		161.5		109.6
Total sales and marketing expense incurred by the LEQEMBI Collaboration	104.6		27.2		9.8
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	52.3		13.6		4.9

Summary of activity related to Aducanumab collaboration

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total ADUHELM development expense	$	149.4	$	183.7	$	152.0
Biogen's share of the ADUHELM Collaboration development expense reflected in research and development expense in our consolidated statements of income	82.2		101.1		83.6
Total ADUHELM sales and marketing expense incurred by the ADUHELM Collaboration Agreement	134.2		562.3		353.0
Biogen's share of the ADUHELM Collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit (loss) sharing in our consolidated statements of income	71.5		301.4		193.7
Total ADUHELM Collaboration third party milestones	—		100.0		75.0
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit (loss) sharing in our consolidated statements of income	—		45.0		33.8

Summary of activity related to the UCB collaboration

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total UCB collaboration development expense	$	68.0	$	84.2	$	58.3
Biogen's share of the UCB collaboration development expense reflected in research and development expense in our consolidated statements of income	34.0		42.1		29.2

Summary of Activity Related to Sage Therapeutics

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total Sage collaboration development expense	$	173.3	$	167.7	$	—
Biogen's share of the Sage collaboration development expense reflected in research and development expense in our consolidated statements of income	86.7		83.8		—
Total Sage sales and marketing expense incurred by the collaboration	109.9		36.4		—
Biogen's share of the Sage collaboration sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	55.0		18.2		—

Summary of Activity Related to Denali Therapeutics Collaboration

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total Denali collaboration development expense	$	75.1	$	42.5	$	14.6
Biogen's share of the Denali collaboration development expense reflected in research and development expense in our consolidated statements of income	43.8		25.5		8.8

Summary of Activity Related to Sangamo Therapeutics

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


	For the Years Ended December 31,
(In millions)	2022		2021		2020
Total Sangamo collaboration development expense	$	19.1	$	22.7	$	10.1
Biogen's share of the Sangamo collaboration development expense reflected in research and development expense in our consolidated statements of income	12.1		14.6		6.4

Segment Information (Tables)

12 Months Ended

Dec. 31, 2022

Segment Reporting [Abstract]

Geographic information

The following tables contain certain financial information by geographic area:


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

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

	December 31, 2020
(In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenue from external customers	$	5,900.1	$	2,495.3	$	1,161.1	$	596.7	$	539.0	$	10,692.2
Revenue from anti-CD20 therapeutic programs	1,897.4		0.1		—		—		80.3		1,977.8
Other revenue from external customers	733.6		8.0		0.1		32.9		—		774.6
Long-lived assets	1,496.3		2,290.2		31.2		16.2		10.9		3,844.8

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

Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Apr. 30, 2022 USD ($)	Mar. 31, 2022	Feb. 29, 2012
Property, Plant and Equipment [Line Items]
Interest in subsidiary (less than given percentage)	100.00%
Number of operating segments \| segment	1
Advertising costs	$ 54.1	$ 98.7	$ 111.8
Samsung Bioepis
Property, Plant and Equipment [Line Items]
Due from joint venture				$ 1,300.0
Samsung Bioepis \| Payment Due At First Anniversary
Property, Plant and Equipment [Line Items]
Due from joint venture				812.5
Samsung Bioepis \| Payment Due At Second Anniversary
Property, Plant and Equipment [Line Items]
Due from joint venture				$ 437.5
Samsung Bioepis
Property, Plant and Equipment [Line Items]
Ownership percentage					49.90%	15.00%
Minimum
Property, Plant and Equipment [Line Items]
Payment terms of accounts receivable arising from product sales	30 days
Minimum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Payment terms of accounts receivable arising from product sales	90 days
Maximum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years

Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2022
Minimum \| Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Minimum \| Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Minimum \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Minimum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Maximum \| Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years
Maximum \| Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	7 years
Maximum \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	20 years
Maximum \| Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years

Acquisitions - (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Acquisitions - (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Acquired in-process research and development		$ 0.0	$ 18.0	$ 75.0
BIIB118
Business Acquisition [Line Items]
Acquired in-process research and development	$ 75.0

Dispositions (Details) ₩ in Millions, $ in Millions	1 Months Ended		12 Months Ended
Dispositions (Details) ₩ in Millions, $ in Millions	Apr. 30, 2022 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2022 KRW (₩)	Dec. 31, 2021 KRW (₩)	Feb. 29, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of equity interest in Samsung Bioepis			$ (277.3)	$ (824.9)	$ 685.7
Samsung Bioepis
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage						49.90%		15.00%	15.00%
Investment in Samsung Bioepis				$ 599.9			₩ 713,300.0	$ 45.0	₩ 49,500.0
Additional milestone payment		$ 25.0
Samsung Bioepis \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other current assets, receivable			798.8
Other assets, receivable			$ 405.4
Samsung Bioepis \| Payment Due At First Anniversary \| Risk-adjusted discount rate \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Risk-adjusted discount rates			0.057
Samsung Bioepis \| Payment Due At Second Anniversary \| Risk-adjusted discount rate \| Fair Value, Recurring
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Risk-adjusted discount rates			0.059
Samsung Bioepis
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of interest in joint venture	$ 1,000.0
Due from joint venture	1,300.0
Investment in Samsung Bioepis \| ₩						₩ 581.6
Gain on sale of equity interest in Samsung Bioepis			$ 1,500.0
Cumulative translation loss			58.9
Gain on derivative used in net investment hedge			57.0
Additional milestone payment	$ 50.0
Contingent discount on common shares	5.00%
Discrete income tax expense (benefit)			257.9
Samsung Bioepis \| Payment Due At First Anniversary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Due from joint venture	$ 812.5
Gain (loss) on sale			10.7
Samsung Bioepis \| Payment Due At Second Anniversary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Due from joint venture	$ 437.5
Gain (loss) on sale			$ (1.4)

Restructuring - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restructuring and Related Activities [Abstract]
Estimated restructuring charges		$ 131.0
Restructuring charges		131.1	$ 0.0	$ 0.0
Restructuring reserve		35.9
Employee related costs		112.6
Gain due to lease termination	$ 5.3
Accelerated depreciation expense		10.4
Other restructuring costs		$ 13.2

Restructuring - Restructuring Reserve Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Expense	$ 131.1	$ 0.0	$ 0.0
Foreign currency and other adjustments	1.3
Restructuring reserve, ending	35.9
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, beginning	0.0
Expense	112.6
Payment	(78.0)
Restructuring reserve, ending	$ 35.9	$ 0.0

Revenue - Revenues by Product (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total product revenue	$ 10,173.4	$ 10,981.7	$ 13,444.6
Fumarate
Disaggregation of Revenue [Line Items]
Total product revenue	1,997.3	2,362.3	3,905.4
Interferon
Disaggregation of Revenue [Line Items]
Total product revenue	1,305.4	1,566.1	1,877.5
TYSABRI
Disaggregation of Revenue [Line Items]
Total product revenue	2,030.9	2,063.1	1,946.1
FAMPYRA
Disaggregation of Revenue [Line Items]
Total product revenue	96.6	105.2	103.1
Subtotal: MS
Disaggregation of Revenue [Line Items]
Total product revenue	5,430.2	6,096.7	7,832.1
SPINRAZA
Disaggregation of Revenue [Line Items]
Total product revenue	1,793.5	1,905.1	2,052.1
ADUHELM
Disaggregation of Revenue [Line Items]
Total product revenue	4.8	3.0	0.0
BENEPALI
Disaggregation of Revenue [Line Items]
Total product revenue	441.0	498.3	481.6
IMRALDI
Disaggregation of Revenue [Line Items]
Total product revenue	224.5	233.4	216.3
FLIXABI
Disaggregation of Revenue [Line Items]
Total product revenue	81.3	99.4	97.9
Subtotal: Biosimilars
Disaggregation of Revenue [Line Items]
Total product revenue	751.1	831.1	795.8
FUMADERM
Disaggregation of Revenue [Line Items]
Total product revenue	8.2	11.0	12.2
Total product revenue
Disaggregation of Revenue [Line Items]
Total product revenue	7,987.8	8,846.9	10,692.2
TECFIDERA
Disaggregation of Revenue [Line Items]
Total product revenue	1,443.9	1,951.9	3,841.1
VUMERITY
Disaggregation of Revenue [Line Items]
Total product revenue	553.4	410.4	64.3
AVONEX
Disaggregation of Revenue [Line Items]
Total product revenue	973.5	1,208.7	1,491.9
PLEGRIDY
Disaggregation of Revenue [Line Items]
Total product revenue	331.9	357.4	385.6
BYOOVIZ
Disaggregation of Revenue [Line Items]
Total product revenue	4.3	0.0	0.0
United States \| Fumarate
Disaggregation of Revenue [Line Items]
Total product revenue	939.0	1,089.5	2,742.0
United States \| Interferon
Disaggregation of Revenue [Line Items]
Total product revenue	797.6	983.1	1,273.5
United States \| TYSABRI
Disaggregation of Revenue [Line Items]
Total product revenue	1,123.4	1,142.2	1,096.8
United States \| FAMPYRA
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| Subtotal: MS
Disaggregation of Revenue [Line Items]
Total product revenue	2,860.0	3,214.8	5,112.3
United States \| SPINRAZA
Disaggregation of Revenue [Line Items]
Total product revenue	600.2	587.9	787.8
United States \| ADUHELM
Disaggregation of Revenue [Line Items]
Total product revenue	4.8	3.0	0.0
United States \| BENEPALI
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| IMRALDI
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| FLIXABI
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| Subtotal: Biosimilars
Disaggregation of Revenue [Line Items]
Total product revenue	4.3	0.0	0.0
United States \| FUMADERM
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
United States \| Total product revenue
Disaggregation of Revenue [Line Items]
Total product revenue	3,469.3	3,805.7	5,900.1
United States \| TECFIDERA
Disaggregation of Revenue [Line Items]
Total product revenue	417.7	680.6	2,677.7
United States \| VUMERITY
Disaggregation of Revenue [Line Items]
Total product revenue	521.3	408.9	64.3
United States \| AVONEX
Disaggregation of Revenue [Line Items]
Total product revenue	649.2	830.2	1,083.4
United States \| PLEGRIDY
Disaggregation of Revenue [Line Items]
Total product revenue	148.4	152.9	190.1
United States \| BYOOVIZ
Disaggregation of Revenue [Line Items]
Total product revenue	4.3	0.0	0.0
Rest of World \| Fumarate
Disaggregation of Revenue [Line Items]
Total product revenue	1,058.3	1,272.8	1,163.4
Rest of World \| Interferon
Disaggregation of Revenue [Line Items]
Total product revenue	507.8	583.0	604.0
Rest of World \| TYSABRI
Disaggregation of Revenue [Line Items]
Total product revenue	907.5	920.9	849.3
Rest of World \| FAMPYRA
Disaggregation of Revenue [Line Items]
Total product revenue	96.6	105.2	103.1
Rest of World \| Subtotal: MS
Disaggregation of Revenue [Line Items]
Total product revenue	2,570.2	2,881.9	2,719.8
Rest of World \| SPINRAZA
Disaggregation of Revenue [Line Items]
Total product revenue	1,193.3	1,317.2	1,264.3
Rest of World \| ADUHELM
Disaggregation of Revenue [Line Items]
Total product revenue	0.0	0.0	0.0
Rest of World \| BENEPALI
Disaggregation of Revenue [Line Items]
Total product revenue	441.0	498.3	481.6
Rest of World \| IMRALDI
Disaggregation of Revenue [Line Items]
Total product revenue	224.5	233.4	216.3
Rest of World \| FLIXABI
Disaggregation of Revenue [Line Items]
Total product revenue	81.3	99.4	97.9
Rest of World \| Subtotal: Biosimilars
Disaggregation of Revenue [Line Items]
Total product revenue	746.8	831.1	795.8
Rest of World \| FUMADERM
Disaggregation of Revenue [Line Items]
Total product revenue	8.2	11.0	12.2
Rest of World \| Total product revenue
Disaggregation of Revenue [Line Items]
Total product revenue	4,518.5	5,041.2	4,792.1
Rest of World \| TECFIDERA
Disaggregation of Revenue [Line Items]
Total product revenue	1,026.2	1,271.3	1,163.4
Rest of World \| VUMERITY
Disaggregation of Revenue [Line Items]
Total product revenue	32.1	1.5	0.0
Rest of World \| AVONEX
Disaggregation of Revenue [Line Items]
Total product revenue	324.3	378.5	408.5
Rest of World \| PLEGRIDY
Disaggregation of Revenue [Line Items]
Total product revenue	183.5	204.5	195.5
Rest of World \| BYOOVIZ
Disaggregation of Revenue [Line Items]
Total product revenue	$ 0.0	$ 0.0	$ 0.0

Revenue - Narrative (Details) $ in Millions	12 Months Ended
Revenue - Narrative (Details) $ in Millions	Dec. 31, 2022 USD ($) wholesaler	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)
Disaggregation of Revenue [Line Items]
Number of wholesalers \| wholesaler	2
Percentage of total revenues	16.70%	15.10%	14.70%
Revenues	$ 10,173.4	$ 10,981.7	$ 13,444.6
Other
Disaggregation of Revenue [Line Items]
Revenues	485.1	476.3	774.6
Contract manufacturing and other revenue
Disaggregation of Revenue [Line Items]
Revenues	$ 417.7	$ 427.7	719.1
Remaining performance obligation, remaining amount			153.8
Remaining performance obligation, amount				$ 500.0
Contract Manufacturing Customer \| Contract manufacturing and other revenue
Disaggregation of Revenue [Line Items]
Revenues			$ 346.2
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors	26.80%	28.80%	30.50%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors	11.10%	10.10%	15.30%
Distributor One
Disaggregation of Revenue [Line Items]
Percentage receivables of wholesale distributor accounted in consolidated receivables	22.70%	21.90%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage receivables of wholesale distributor accounted in consolidated receivables	10.90%	10.20%

Revenue - Reserves for Discounts and Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 935.3	$ 1,276.0	$ 1,198.9
Current provisions relating to sales in current year	3,394.4	3,700.6	4,102.5
Adjustments relating to prior years	(8.6)	(103.4)	(53.7)
Payments/credits relating to sales in current year	(2,576.8)	(2,882.8)	(3,061.2)
Payments/credits relating to sales in prior years	(709.3)	(1,055.1)	(910.5)
Ending balance	1,035.0	935.3	1,276.0
Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	137.7	141.4	131.1
Current provisions relating to sales in current year	666.6	736.7	774.7
Adjustments relating to prior years	(2.8)	(4.0)	(1.0)
Payments/credits relating to sales in current year	(514.9)	(599.3)	(635.1)
Payments/credits relating to sales in prior years	(132.8)	(137.1)	(128.3)
Ending balance	153.8	137.7	141.4
Contractual Adjustments
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	759.6	1,093.0	1,027.3
Current provisions relating to sales in current year	2,715.5	2,948.7	3,308.8
Adjustments relating to prior years	1.4	(96.1)	(54.0)
Payments/credits relating to sales in current year	(2,060.7)	(2,283.1)	(2,426.1)
Payments/credits relating to sales in prior years	(558.1)	(902.9)	(763.0)
Ending balance	857.7	759.6	1,093.0
Returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	38.0	41.6	40.5
Current provisions relating to sales in current year	12.3	15.2	19.0
Adjustments relating to prior years	(7.2)	(3.3)	1.3
Payments/credits relating to sales in current year	(1.2)	(0.4)	0.0
Payments/credits relating to sales in prior years	(18.4)	(15.1)	(19.2)
Ending balance	$ 23.5	$ 38.0	$ 41.6

Revenue - Total Reserves for Discounts and Allowances (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	$ 1,035.0	$ 935.3	$ 1,276.0	$ 1,198.9
Reduction of accounts receivable
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	143.4	133.2
Component of accrued expense and other
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	$ 891.6	$ 802.1

Revenue - Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 10,173.4	$ 10,981.7	$ 13,444.6
Royalty Attributed To OCREVUS
Disaggregation of Revenue [Line Items]
Revenue	1,136.3	991.7	845.4
Revenue from anti-CD20 therapeutic programs
Disaggregation of Revenue [Line Items]
Revenue	1,700.5	1,658.5	1,977.8
Genentech
Disaggregation of Revenue [Line Items]
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0	647.7	1,080.2
Royalty revenue on sales of OCREVUS	$ 17.2	$ 19.1	$ 52.2

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Revenue - Other Revenues (Details) - USD ($) $ in Millions	12 Months Ended
Revenue - Other Revenues (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total product revenue	$ 10,173.4	$ 10,981.7	$ 13,444.6
Royalty revenue
Disaggregation of Revenue [Line Items]
Total product revenue	67.4	48.6	55.5
Contract manufacturing and other revenue
Disaggregation of Revenue [Line Items]
Total product revenue	417.7	427.7	719.1
Total other revenue
Disaggregation of Revenue [Line Items]
Total product revenue	$ 485.1	$ 476.3	$ 774.6

- Definition

+ References

+ Details

Inventory - Components of Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Inventory [Line Items]
Raw materials	$ 413.2	$ 349.6
Work in process	751.9	814.0
Finished goods	200.4	187.9
Total inventory	1,365.5	1,351.5
Inventory, current	1,344.4	1,351.5
Inventory, noncurrent	21.1	$ 0.0
LEOEMBI
Inventory [Line Items]
Work in process	$ 89.8

Inventory - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
Inventory - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Inventory [Line Items]
Write-downs on excess, obsolete, unmarketable or other inventory					$ 336.2	$ 167.6	$ 26.6
Inventory		$ 1,351.5			1,365.5	1,351.5
Income (loss) from equity method investments					2.6	34.9	3.3
Eisai
Inventory [Line Items]
Income (loss) from equity method investments				$ 33.8	0.0	45.0	$ 33.8
ADUHELM
Inventory [Line Items]
Write-downs on excess, obsolete, unmarketable or other inventory	$ 275.0	120.0
Inventory		$ 223.0				223.0
Income (loss) from equity method investments					111.0	30.0
ADUHELM \| Eisai
Inventory [Line Items]
Income (loss) from equity method investments			$ 45.0			$ 59.0
ADUHELM \| Centers for Medicare and Medicaid Service \| Eisai
Inventory [Line Items]
Income (loss) from equity method investments					$ 136.0

Intangible Assets and Goodwill - Summary of Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 7,479.3	$ 7,609.8
Accumulated Amortization	(5,629.2)	(5,388.5)
Total intangible assets	1,850.1	2,221.3
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	215.0
Finite-Lived Intangible Assets, Amortization Expense, Year Two	195.0
Finite-Lived Intangible Assets, Amortization Expense, Year Three	190.0
Finite-Lived Intangible Assets, Amortization Expense, Year Four	175.0
2027	165.0
Out Licensed Patents
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(5,629.2)	(5,388.5)
Net	1,786.1	2,024.6
Finite-Lived Intangible Assets, Gross	$ 7,415.3	7,413.1
Minimum \| Out Licensed Patents
Finite-Lived Intangible Assets [Line Items]
Estimated life	4 years
Maximum \| Out Licensed Patents
Finite-Lived Intangible Assets [Line Items]
Estimated life	28 years
In-process research and development
Finite-Lived Intangible Assets [Line Items]
Cost and net	$ 0.0	132.7
Accumulated Amortization	0.0	0.0
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Cost and net	64.0	64.0
Accumulated Amortization	$ 0.0	$ 0.0

Intangible Assets and Goodwill - Narrative (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2022	Sep. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Line Items]
Amortization and impairment of acquired intangible assets					$ 365,900,000	$ 881,300,000	$ 464,800,000
Amortization of acquired intangible assets					246,300,000	$ 252,000,000	255,100,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]						Amortization and impairment of acquired intangible assets
(Gain) loss on fair value remeasurement of contingent consideration					(209,100,000)	$ (50,700,000)	(86,300,000)
Accumulated impairment losses related to goodwill	$ 0				0
Goodwill	5,749,000,000			$ 5,762,100,000	5,749,000,000	5,761,100,000	5,762,100,000
Other					(12,100,000)	(1,000,000.0)
In-process research and development
Goodwill [Line Items]
Intangible assets (excluding goodwill)	0				0	132,700,000
BIIB111
Goodwill [Line Items]
Impairment of intangible assets						365,000,000	115,000,000
BIIB111 \| In-process research and development
Goodwill [Line Items]
Intangible asset, fair value	0	$ 0			0
BIIB112
Goodwill [Line Items]
Impairment of intangible assets		220,000,000
BIIB112 \| In-process research and development
Goodwill [Line Items]
Intangible asset, fair value	0	0			0
BIIB054
Goodwill [Line Items]
Impairment of intangible assets							75,400,000
In Process Research and Development Other
Goodwill [Line Items]
Impairment of intangible assets							19,300,000
TGN
Goodwill [Line Items]
(Gain) loss on fair value remeasurement of contingent consideration					209,100,000
TGN \| In-process research and development
Goodwill [Line Items]
Impairment of intangible assets	$ 119,600,000		$ 44,300,000
BIIB111 and BIIB112
Goodwill [Line Items]
Manufacturing and other costs		$ 39,100,000
Convergence Pharmaceuticals \| TGN \| In-process research and development
Goodwill [Line Items]
Acquired intangible asset					424,600,000
Nightstar \| BIIB111
Goodwill [Line Items]
Impairment of intangible assets						365,000,000
Nightstar \| BIIB111 \| In-process research and development
Goodwill [Line Items]
Impairment of intangible assets				115,000,000
Acquired intangible asset					480,000,000
Nightstar \| BIIB112
Goodwill [Line Items]
Impairment of intangible assets						$ 220,000,000
Nightstar \| BIIB112 \| In-process research and development
Goodwill [Line Items]
Acquired intangible asset					220,000,000
Nightstar \| BIIB054
Goodwill [Line Items]
Impairment of intangible assets				75,400,000
Intangible asset, fair value				$ 0			$ 0
Biogen International Neuroscience GmbH \| BIIB054 \| In-process research and development
Goodwill [Line Items]
Acquired intangible asset					$ 110,900,000

Intangible Assets and Goodwill - Estimated Future Amortization of Intangible Assets (Details) $ in Millions	Dec. 31, 2022 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2023	$ 215.0
2024	195.0
2025	190.0
2026	175.0
2027	$ 165.0

Intangible Assets and Goodwill - Changes in Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Goodwill, beginning of year	$ 5,761.1	$ 5,762.1
Other	(12.1)	(1.0)
Goodwill, end of year	$ 5,749.0	$ 5,761.1

- 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

Fair Value Measurements - Summary of Assets and Liabilities Recorded at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets:
Marketable debt securities	$ 2,179.2	$ 2,433.1
Fair value, measurements, recurring
Assets:
Cash equivalents	2,847.6	1,632.2
Marketable equity securities	791.1	1,048.5
Derivative contracts	63.0	80.9
Plan assets for deferred compensation	32.8	33.4
Total	7,117.9	5,228.1
Liabilities:
Derivative contracts	26.0	10.8
Contingent consideration obligations	0.0	209.1	$ 259.8
Total	26.0	219.9
Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	798.8
Receivable from Samsung BioLogics	405.4
Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities	1,231.6	1,108.2
Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities	810.3	1,192.7
Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities	137.3	132.2
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	791.1	181.7
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	791.1	181.7
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration obligations		0.0
Total	0.0	0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	0.0
Receivable from Samsung BioLogics	0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) \| Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities	0.0	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	0.0
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring
Assets:
Cash equivalents	2,847.6	1,632.2
Marketable equity securities	0.0	866.8
Derivative contracts	63.0	80.9
Plan assets for deferred compensation	32.8	33.4
Total	5,122.6	5,046.4
Liabilities:
Derivative contracts	26.0	10.8
Contingent consideration obligations		0.0
Total	26.0	10.8
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	0.0
Receivable from Samsung BioLogics	0.0
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities	1,231.6	1,108.2
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities	810.3	1,192.7
Significant Other Observable Inputs (Level 2) \| Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities	137.3	132.2
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	0.0	0.0
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	1,204.2	0.0
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration obligations	0.0	209.1
Total	0.0	209.1
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Samsung Bioepis
Assets:
Receivable from Samsung BioLogics	798.8
Receivable from Samsung BioLogics	405.4
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Government securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Fair value, measurements, recurring \| Mortgage and other asset backed securities
Assets:
Marketable debt securities	$ 0.0	$ 0.0

Fair Value Measurements - Summary of Significant Unobservable Inputs (Details) $ in Millions	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Risk-adjusted discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate		0.0130
Weighted Average \| Risk-adjusted discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0	0.0130
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration obligations	$ 0.0	$ 209.1	$ 259.8
Fair Value, Recurring \| Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration obligations	$ 0.0	$ 209.1

Fair Value Measurements - Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended		12 Months Ended
Fair Value Measurements - Narrative (Details) - USD ($)	Feb. 28, 2015	Dec. 31, 2010	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business Acquisition, Contingent Consideration [Line Items]
Impairment of assets					$ 0	$ 0
Technological and regulatory success, probability						10.90%
Convergence Pharmaceuticals
Business Acquisition, Contingent Consideration [Line Items]
Additions	$ 274,500,000
Contingent consideration obligations					209,100,000	$ 209,100,000
Biogen Idec International Neuroscience GmbH
Business Acquisition, Contingent Consideration [Line Items]
Additions		$ 81,200,000					$ 0
Contingent consideration obligations				$ 101,500,000			101,500,000
Other long-term liabilities
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration obligations						209,100,000
BIIB111
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets						365,000,000	115,000,000
BIIB111 \| In-process research and development
Business Acquisition, Contingent Consideration [Line Items]
Intangible asset, fair value			$ 0		0
BIIB111 \| Nightstar
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets						365,000,000
BIIB112
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets			220,000,000
BIIB112 \| In-process research and development
Business Acquisition, Contingent Consideration [Line Items]
Intangible asset, fair value			$ 0		0
BIIB112 \| Nightstar
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets						$ 220,000,000
BIIB054
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets							75,400,000
Reduction in contingent consideration					$ 195,400,000
BIIB054 \| Nightstar
Business Acquisition, Contingent Consideration [Line Items]
Impairment of intangible assets				75,400,000
Intangible asset, fair value				$ 0			$ 0

Fair Value Measurements - Summary of Fair and Carrying Value of Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Feb. 28, 2021	Apr. 30, 2020
Debt Instrument
Interest rate on senior notes	3.625%
Senior Notes
Debt Instrument
Notes payable, fair value	$ 5,410.2	$ 8,004.7
3.625% Senior Notes due September 15, 2022(1) \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 0.0	1,020.0
Interest rate on senior notes	3.625%
4.050% Senior Notes due September 15, 2025 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,699.9	1,895.2
Interest rate on senior notes	4.05%
2.250% Senior Notes due May 1, 2030 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,219.0	1,475.9
Interest rate on senior notes	2.25%			2.25%
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 1,033.2	1,463.0
Interest rate on senior notes	5.20%		5.20%
3.150% Senior Notes due May 1, 2050 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 989.0	1,457.7
Interest rate on senior notes	3.15%			3.15%
3.250% Senior Notes due February 15, 2051 \| Senior Notes
Debt Instrument
Notes payable, fair value	$ 469.1	$ 692.9
Interest rate on senior notes	3.25%		3.25%

Fair Value Measurements - Fair Value of Contingent Consideration Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	$ (209.1)	$ (50.7)	$ (86.3)
Fair value, measurements, recurring
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of year	209.1	259.8
Fair value, end of year	$ 0.0	$ 209.1	$ 259.8

Financial Instruments - Summary of Financial Assets with Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	$ 2,847.6	$ 1,632.2
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	177.2	247.6
Overnight reverse repurchase agreements
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	59.0	200.0
Money market funds
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	2,581.5	901.6
Short-term debt securities
Cash and Cash Equivalents [Line Items]
Cash equivalents, total	$ 29.9	$ 283.0

Financial Instruments - Summary of Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Marketable debt securities:
Amortized Cost	$ 2,199.1	$ 2,435.9
Gross Unrealized Gains	0.3	0.4
Gross Unrealized Losses	(20.2)	(3.2)
Fair Value	2,179.2	2,433.1
Marketable equity securities:
Amortized Cost	1,133.8	1,167.0
Gross Unrealized Gains	0.0	160.9
Gross Unrealized Losses	(342.7)	(279.4)
Fair Value	791.1	1,048.5
Corporate debt securities Current
Marketable debt securities:
Amortized Cost	936.2	723.6
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	(4.9)	(0.3)
Fair Value	931.3	723.4
Corporate debt securities Non-current
Marketable debt securities:
Amortized Cost	305.3	385.4
Gross Unrealized Gains	0.1	0.2
Gross Unrealized Losses	(5.1)	(0.8)
Fair Value	300.3	384.8
Government securities Current
Marketable debt securities:
Amortized Cost	547.1	817.0
Gross Unrealized Gains	0.1	0.0
Gross Unrealized Losses	(5.0)	(0.4)
Fair Value	542.2	816.6
Government securities Non-current
Marketable debt securities:
Amortized Cost	271.4	377.0
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	(3.3)	(1.0)
Fair Value	268.1	376.1
Mortgage and other asset backed securities Current
Marketable debt securities:
Amortized Cost	0.0	1.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	0.0	1.1
Mortgage and other asset backed securities Non-current
Marketable debt securities:
Amortized Cost	139.1	131.8
Gross Unrealized Gains	0.1	0.0
Gross Unrealized Losses	(1.9)	(0.7)
Fair Value	137.3	131.1
Marketable equity securities, current
Marketable equity securities:
Amortized Cost	1,133.8	33.9
Gross Unrealized Gains	0.0	9.9
Gross Unrealized Losses	(342.7)	0.0
Fair Value	$ 791.1	43.8
Marketable equity securities, non-current
Marketable equity securities:
Amortized Cost		1,133.1
Gross Unrealized Gains		151.0
Gross Unrealized Losses		(279.4)
Fair Value		$ 1,004.7

Financial Instruments - Summary of Contractual Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Estimated Fair Value
Due in one year or less	$ 1,473.5	$ 1,541.1
Due after one year through five years	694.4	868.2
Due after five years	11.3	23.8
Total marketable debt securities	2,179.2	2,433.1
Amortized Cost
Due in one year or less	1,483.3	1,541.7
Due after one year through five years	703.7	870.2
Due after five years	12.1	24.0
Amortized Cost	$ 2,199.1	$ 2,435.9

Financial Instruments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Average maturity of marketable securities, months	8 months	10 months
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio	$ 846.0	$ 1,110.3

Financial Instruments - Proceeds from Marketable Debt Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Investments, All Other Investments [Abstract]
Proceeds from maturities and sales	$ 3,671.0	$ 3,405.4	$ 7,299.4
Realized gains	0.0	0.2	17.7
Realized losses	$ 12.6	$ 4.0	$ 26.0

Derivative Instruments - Narrative (Details) $ in Millions, ₩ in Billions	1 Months Ended			12 Months Ended
	May 31, 2020 USD ($)	Nov. 30, 2018 USD ($)	Nov. 30, 2018 KRW (₩)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2022	May 31, 2018	Feb. 29, 2012
Derivatives, Fair Value [Line Items]
Range of durations of foreign currency forward contracts				12 months
Interest rate on senior notes				3.625%
Net gains (losses) of other income (expense) related to foreign currency forward contracts				$ (34.7)	$ 43.3	$ 30.1
Net investment hedge
Derivatives, Fair Value [Line Items]
Derivative qualifying as hedge gain (loss), excluded component, after tax					(3.6)
Samsung Bioepis
Derivatives, Fair Value [Line Items]
Ownership percentage before additional purchase transaction								5.00%
Ownership percentage							49.90%		15.00%
Payments to increase investment in Samsung Bioepis		$ 676.6	₩ 759.5
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount				1,715.5	2,126.8
Not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount				1,238.8	1,268.0
Foreign Exchange Forward
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) on derivative instruments				8.6	53.8	$ (212.5)
Foreign Exchange Forward \| Net investment hedge
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) on derivative instruments					$ 10.6
Interest rate swap \| Interest Expense
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments, net, pretax	$ 3.3
Interest rate swap \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount				$ 675.0
Minimum
Derivatives, Fair Value [Line Items]
Range of durations of foreign currency forward contracts				1 month	1 month
Maximum
Derivatives, Fair Value [Line Items]
Range of durations of foreign currency forward contracts				12 months	15 months

Derivative Instruments - Foreign Currency Forward Contracts Entered into Hedge Forecasted Revenues (Details) - Designated as Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts	$ 1,715.5	$ 2,126.8
Euro
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts	1,495.5	1,828.0
British pound
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts	162.8	166.2
Japanese yen
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts	0.0	72.7
Canadian dollar
Derivatives, Fair Value [Line Items]
Total foreign currency forward contracts	$ 57.2	$ 59.9

Derivative Instruments - Summary of Unrealized Gain (Loss) on Derivative Instruments Included in AOCI (Details) - Foreign Exchange Forward - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains	$ 29.9	$ 60.8	$ 0.0
Unrealized (losses)	(21.3)	(7.0)	(212.5)
Net unrealized gains (losses)	$ 8.6	$ 53.8	$ (212.5)

Derivative Instruments - Summary of the Effect of Derivatives Designated as Cash Flow Hedging Instruments (Details) - Foreign exchange contract - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)	$ 201.6	$ (60.0)	$ 18.3
Operating expense
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)	(5.5)	(0.8)	3.3
Cash flows, revenue \| Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)	(8.6)	(8.4)	(9.9)
Cash flows, operating expenses \| Operating expense
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)	$ 0.0	$ 0.0	$ 0.0

Derivative Instruments - Summary of the Effect of Derivatives Designated as Net Investment Hedging Instruments (Details) - Net investment hedge - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Recognized in Other Comprehensive Income (Effective Portion) (in millions)	$ 20.4	$ 46.0	$ (35.1)
Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions)	(3.2)	(3.2)	4.5
Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains/(Losses) Recognized in Net Income (Amounts Excluded from Effectiveness Testing) (in millions)	$ (4.6)	$ (0.6)	$ 2.9

Derivative Instruments - Summary of the Fair Value for our Outstanding Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Other current assets \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Asset derivative instruments	$ 37.9	$ 66.2
Other current assets \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Asset derivative instruments	25.1	5.1
Other current assets \| Foreign exchange contract \| Net investment hedge
Derivative Instruments, Gain (Loss) [Line Items]
Asset derivative instruments	0.0	4.1
Investments and other assets \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Asset derivative instruments	0.0	5.5
Accrued expense and other \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Liability derivative instruments	18.4	6.6
Accrued expense and other \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Liability derivative instruments	$ 7.6	$ 4.2

Property, Plant and Equipment - Components of property, plant, and equipment, net (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Land	$ 202.4		$ 207.5
Buildings	1,592.9		1,699.7
Leasehold improvements	107.7		121.0
Machinery and equipment	1,611.5		1,585.5
Computer software and hardware	999.9		971.6
Furniture and fixtures	61.1		67.4
Construction in progress	888.8		770.3
Total cost	5,464.3		5,423.0
Less: accumulated depreciation	(2,165.7)		(2,006.6)
Total property, plant and equipment, net	$ 3,298.6		$ 3,416.4
125 Broadway Building
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		$ 79.2
125 Broadway Building \| Buildings
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		72.6
125 Broadway Building \| Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		1.6
125 Broadway Building \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net		$ 5.0

Property, Plant and Equipment - Narrative (Details) ft² in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) ft²	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)
Property, Plant and Equipment [Line Items]
Depreciation expense		$ 272.4	$ 235.3	$ 201.9
Interest costs capitalized		17.1	36.3	65.2
Construction in progress		888.8	770.3
Property, plant and equipment, gross		5,464.3	5,423.0
Proceeds from divestiture of Hillerød, Denmark manufacturing operations		0.0	28.1	0.0
Gain on sale of building		503.7	0.0	$ 0.0
Property, plant and equipment, net		3,298.6	3,416.4
125 Broadway Building
Property, Plant and Equipment [Line Items]
Proceeds from divestiture of Hillerød, Denmark manufacturing operations	$ 603.0
Tenant allowance	10.8
Gain on sale of building	503.7
Property, plant and equipment, net	79.2
125 Broadway Building \| Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	72.6
125 Broadway Building \| Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	1.6
125 Broadway Building \| Machinery and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 5.0
Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Construction in progress		$ 711.1	$ 677.0
Property, plant and equipment, gross					$ 1,200.0
Biologics Manufacturing \| Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²		393
Warehouse, Utilities and Support Space \| Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²		290
Administrative Space \| Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Number of square feet \| ft²		51

Leases - Narrative (Details) - USD ($) $ in Millions	1 Months Ended
Leases - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Operating Leased Assets [Line Items]
Present value of operating lease liabilities		$ 430.2	$ 419.5
Operating lease assets		$ 403.9	$ 375.4
Operating Lease, Right-Of-Use Asset, Derecognized	$ 47.4
Operating Lease, Liability, Derecognized	52.7
Gain due to lease termination	$ 5.3
Buildings
Operating Leased Assets [Line Items]
Operating lease, contract term		5 years 6 months
Present value of operating lease liabilities		$ 168.2
Operating lease assets		$ 168.2
Minimum
Operating Leased Assets [Line Items]
Operating lease, contract term		1 year
Operating lease, renewal term		1 year
Minimum \| Sublease
Operating Leased Assets [Line Items]
Operating lease, contract term		2 years
Maximum
Operating Leased Assets [Line Items]
Operating lease, contract term		8 years
Operating lease, renewal term		6 years
Maximum \| Sublease
Operating Leased Assets [Line Items]
Operating lease, contract term		6 years

Leases - Schedule of Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease assets	$ 403.9	$ 375.4
Operating lease liability, current	97.2	89.1
Long-term operating lease liabilities	333.0	330.4
Present value of operating lease liabilities	430.2	419.5
Cash paid for amounts included in the measurement of lease liabilities	107.4	105.8	$ 100.2
Operating lease assets obtained in exchange for lease obligations	$ 108.3	$ 18.1	$ 59.0
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Operating lease assets	Operating lease assets
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term operating lease liabilities	Long-term operating lease liabilities

Leases - Operating Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net lease cost	$ 95.6	$ 97.9	$ 92.4
Research and development
Operating lease cost	2.0	3.4	5.2
Variable lease cost	0.4	0.8	1.1
Selling, general and administrative
Operating lease cost	95.9	95.9	93.1
Variable lease cost	25.4	25.7	21.1
Sublease income	(24.0)	(23.9)	(24.2)
Other (income) expense, net
Sublease income	$ (4.1)	$ (4.0)	$ (3.9)

Leases - Operating Lease Liability Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
2023	$ 111.0
2024	107.0
2025	80.5
2026	65.7
2027	69.5
Thereafter	36.6
Total lease payments	470.3
Less: interest	40.1
Present value of operating lease liabilities	$ 430.2	$ 419.5

Leases - Operating Lease Weighted Average Remaining Term and Discount Rate (Details)	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Weighted average remaining lease term in years	4 years 7 months 20 days	5 years 5 months 4 days
Weighted average discount rate	3.70%	2.90%

Leases - Operating Lease Supplemental Cash Flow Disclosure (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 107.4	$ 105.8	$ 100.2
Operating lease assets obtained in exchange for lease obligations	$ 108.3	$ 18.1	$ 59.0

Indebtedness - Summary of Indebtedness (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Feb. 28, 2021	Apr. 30, 2020
Non-current portion:
Non-current portion of notes payable	$ 6,567.3
Interest rate on senior notes	3.625%
Senior Notes
Current portion:
Current portion of notes payable	$ 0.0	$ 999.1
Non-current portion:
Non-current portion of notes payable	6,281.0	6,274.0
3.625% Senior Notes due September 15, 2022(1) \| Senior Notes
Current portion:
Current portion of notes payable	$ 0.0	999.1
Non-current portion:
Interest rate on senior notes	3.625%
4.050% Senior Notes due September 15, 2025 \| Senior Notes
Non-current portion:
Non-current portion of notes payable	$ 1,744.7	1,742.9
Interest rate on senior notes	4.05%
2.250% Senior Notes due May 1, 2030 \| Senior Notes
Non-current portion:
Non-current portion of notes payable	$ 1,492.9	1,492.0
Interest rate on senior notes	2.25%			2.25%
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Non-current portion:
Non-current portion of notes payable	$ 1,100.3	1,099.9
Interest rate on senior notes	5.20%		5.20%
3.150% Senior Notes due May 1, 2050 \| Senior Notes
Non-current portion:
Non-current portion of notes payable	$ 1,473.8	1,473.2
Interest rate on senior notes	3.15%			3.15%
3.250% Senior Notes due February 15, 2051 \| Senior Notes
Non-current portion:
Non-current portion of notes payable	$ 469.3	$ 466.0
Interest rate on senior notes	3.25%		3.25%

Indebtedness - Exchange Offer (Details) - USD ($)	1 Months Ended		12 Months Ended
Indebtedness - Exchange Offer (Details) - USD ($)	Jul. 31, 2022	Feb. 28, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Sep. 15, 2015
Debt Instrument
Aggregate principal amount, debt converted	$ 2,400,000
Aggregate principal amount						$ 1,000,000,000
Aggregate cash payments			$ 0	$ 0	$ 1,500,000,000
Interest expense			246,600,000	$ 253,600,000	$ 222,500,000
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Debt Instrument
Aggregate principal amount, debt converted		$ 8,900,000
Aggregate cash payments		12,100,000
Loss on extinguishment of debt		3,200,000
Cash payments on debt extinguishment, including accrued interest		13,800,000
Interest expense		6,100,000
5.200% Senior Notes due September 15, 2045 \| Senior Notes
Debt Instrument
Aggregate principal amount, debt converted		624,600,000
Aggregate principal amount			$ 1,120,000,000
Aggregate cash payments		151,800,000
3.250% Senior Notes due February 15, 2051 \| Senior Notes
Debt Instrument
Aggregate principal amount		$ 700,700,000

Indebtedness - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	May 31, 2020	Jan. 31, 2020	Dec. 31, 2022	Dec. 31, 2020	Sep. 15, 2022	Feb. 28, 2021	Apr. 30, 2020	Sep. 15, 2015
Debt Instrument
Senior notes aggregate principal amount								$ 1,000,000,000
Interest rate on senior notes			3.625%
Redemption rate					99.92%
Revolving Credit Facility
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity		$ 1,000,000,000
Debt instrument, term		5 years
Outstanding borrowings			$ 0
Interest Expense \| Interest rate swap
Debt Instrument
Gain (loss) on derivative instruments, net, pretax	$ 3,300,000
2015 Senior Notes
Debt Instrument
Redemptions percentage of 2015 notes			100.00%
Redemption percentage for change in control provision			101.00%
Senior Notes \| Interest Expense \| Interest rate swap
Debt Instrument
Gain (loss) on derivative instruments, net, pretax				$ 3,300,000
Senior Notes \| 2020 Senior Notes
Debt Instrument
Senior notes aggregate principal amount							$ 3,000,000,000
Redemptions percentage of 2015 notes			100.00%
Redemption percentage for change in control provision			101.00%
Costs associated with the senior notes offerings			$ 24,400,000
Senior Notes \| 2.250% Senior Notes due May 1, 2030
Debt Instrument
Senior notes aggregate principal amount							$ 1,500,000,000
Interest rate on senior notes			2.25%				2.25%
Redemption percentage par value of senior notes							99.973%
Senior Notes \| 3.150% Senior Notes due May 1, 2050
Debt Instrument
Senior notes aggregate principal amount							$ 1,500,000,000
Interest rate on senior notes			3.15%				3.15%
Redemption percentage par value of senior notes							99.174%
Senior Notes \| 2015 Senior Notes
Debt Instrument
Costs associated with the senior notes offerings			$ 47,500,000
Senior Notes \| 3.625% Senior Notes due September 15, 2022(1)
Debt Instrument
Interest rate on senior notes			3.625%
Senior Notes \| 4.050% Senior Notes due September 15, 2025
Debt Instrument
Senior notes aggregate principal amount			$ 1,750,000,000
Interest rate on senior notes			4.05%
Redemption percentage par value of senior notes			99.764%
Senior Notes \| 5.200% Senior Notes due September 15, 2045
Debt Instrument
Senior notes aggregate principal amount			$ 1,120,000,000
Interest rate on senior notes			5.20%			5.20%
Redemption percentage par value of senior notes			99.294%
Senior Notes \| 2.900% Senior Notes due September 15, 2020
Debt Instrument
Senior notes aggregate principal amount								$ 1,500,000,000
Interest rate on senior notes	2.90%
Redemption percentage par value of senior notes								99.792%
Pre-tax charge				$ 12,700,000
Senior Notes \| 2.900% Senior Notes due September 15, 2020 \| Interest Expense
Debt Instrument
Pre-tax charge	$ 9,400,000

Indebtedness - Total Debt Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
2023	$ 0.0
2024	0.0
2025	1,750.0
2026	0.0
2027	0.0
2028 and thereafter	4,817.3
Total debt	6,567.3
Less: debt discount and issuance fees	(286.3)
Notes payable	$ 6,281.0	$ 6,274.0

Equity - Narrative (Details) - USD ($)	12 Months Ended
Equity - Narrative (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Oct. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	8,000,000
Preferred stock, shares issued (in shares)	0	0	0
Preferred stock, shares outstanding (in shares)	0	0	0
Payments for repurchase of common stock	$ 750,000,000.0	$ 1,800,000,000	$ 6,679,100,000
2020 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases				$ 5,000,000,000
Repurchase of common stock, at cost (in shares)	3,600,000	6,000,000	1,600,000
Payments for repurchase of common stock	$ 750,000,000	$ 1,800,000,000	$ 400,000,000
Remaining authorized amount of share repurchases	$ 2,100,000,000
December 2019 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases					$ 5,000,000,000
Repurchase of common stock, at cost (in shares)			16,700,000
Payments for repurchase of common stock			$ 5,000,000,000
March 2019 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases						$ 5,000,000,000
Repurchase of common stock, at cost (in shares)			4,100,000
Payments for repurchase of common stock			$ 1,300,000,000
Series A
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1,750,000
Series X junior participating
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1,000,000
Undesignated
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	5,250,000

Equity - Summary of Common Stock (Details) - shares shares in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Equity [Abstract]
Common stock authorized (in shares)	1,000.0	1,000.0	1,000.0
Common stock issued (in shares)	167.9	170.8	176.2
Common stock outstanding (in shares)	144.0	147.0	152.4

Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	$ (106.7)
Other comprehensive income (loss) before reclassifications	87.0	$ 134.1	$ (145.6)
Amounts reclassified from accumulated other comprehensive income (loss)	(145.2)	58.2	(18.2)
Total other comprehensive income (loss), net of tax	(58.2)	192.3	(163.8)
AOCI, ending balance	(164.9)	(106.7)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	(106.7)	(299.0)	(135.2)
AOCI, ending balance	(164.9)	(106.7)	(299.0)
Unrealized Gains (Losses) on Securities Available for Sale, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	(2.2)	1.4	4.2
Other comprehensive income (loss) before reclassifications	(23.5)	(6.6)	(9.3)
Amounts reclassified from accumulated other comprehensive income (loss)	10.0	3.0	6.5
Total other comprehensive income (loss), net of tax	(13.5)	(3.6)	(2.8)
AOCI, ending balance	(15.7)	(2.2)	1.4
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	53.8	(179.0)	7.8
Other comprehensive income (loss) before reclassifications	137.3	178.2	(165.0)
Amounts reclassified from accumulated other comprehensive income (loss)	(176.0)	54.6	(21.8)
Total other comprehensive income (loss), net of tax	(38.7)	232.8	(186.8)
AOCI, ending balance	15.1	53.8	(179.0)
Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	25.5	(8.5)	25.1
Other comprehensive income (loss) before reclassifications	12.6	33.4	(30.7)
Amounts reclassified from accumulated other comprehensive income (loss)	(38.1)	0.6	(2.9)
Total other comprehensive income (loss), net of tax	(25.5)	34.0	(33.6)
AOCI, ending balance	0.0	25.5	(8.5)
Unrealized Gains (Losses) on Pension Benefit Obligation, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	(44.8)	(66.3)	(32.8)
Other comprehensive income (loss) before reclassifications	43.7	21.5	(33.5)
Amounts reclassified from accumulated other comprehensive income (loss)	0.0	0.0	0.0
Total other comprehensive income (loss), net of tax	43.7	21.5	(33.5)
AOCI, ending balance	(1.1)	(44.8)	(66.3)
Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI, beginning balance	(139.0)	(46.6)	(139.5)
Other comprehensive income (loss) before reclassifications	(83.1)	(92.4)	92.9
Amounts reclassified from accumulated other comprehensive income (loss)	58.9	0.0	0.0
Total other comprehensive income (loss), net of tax	(24.2)	(92.4)	92.9
AOCI, ending balance	$ (163.2)	$ (139.0)	$ (46.6)

Equity - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other (income) expense	$ (108.2)	$ 1,095.5	$ (497.4)
Income tax (benefit) expense	632.8	52.5	992.3
Revenue	10,173.4	10,981.7	13,444.6
Net income attributable to Biogen Inc.	3,046.9	1,556.1	4,000.6
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income attributable to Biogen Inc.	145.2	(58.2)	18.2
Gains (losses) on securities available for sale \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income tax (benefit) expense	2.6	0.8	1.7
Other Operating Income (Expense), Net	(12.6)	(3.8)	(8.2)
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]
Income tax (benefit) expense	(19.8)	6.0	(0.1)
Revenue	201.6	(60.0)	18.3
Operating expense	(5.5)	(0.8)	3.3
Other Operating Income (Expense), Net	(0.3)	0.2	0.3
Gains (losses) on net investment hedges(1) \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Operating Income (Expense), Net	38.1	(0.6)	2.9
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Operating Income (Expense), Net	$ (58.9)	$ 0.0	$ 0.0

Earnings per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net income attributable to Biogen Inc.	$ 3,046.9	$ 1,556.1	$ 4,000.6
Denominator:
Weighted average number of common shares outstanding (in shares)	145,300	149,100	160,900
Effect of dilutive securities:
Dilutive potential common shares (in shares)	700	500	400
Shares used in calculating diluted earnings per share (in shares)	146,000	149,600	161,300
Time-vested restricted stock units
Effect of dilutive securities:
Dilutive securities (in shares)	500	300	200
Market stock units
Effect of dilutive securities:
Dilutive securities (in shares)	100	100	100
Performance stock units settled in stock
Effect of dilutive securities:
Dilutive securities (in shares)	100	100	100

Earnings per Share - Narrative (Details) shares in Millions	12 Months Ended
Earnings per Share - Narrative (Details) shares in Millions	Dec. 31, 2020 shares
Earnings Per Share [Abstract]
Repurchase of common stock (in shares)	22.4

Share-Based Payments - Share-based Compensation Expense Included in Consolidation Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ (263.5)	$ (246.6)	$ (204.5)
Subtotal	273.6	258.8	211.3
Capitalized share-based compensation costs	(9.3)	(8.0)	(6.2)
Share-based compensation expense included in total cost and expense	264.3	250.8	205.1
Income tax effect	(49.2)	(46.7)	(33.5)
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	98.5	89.3	80.0
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	175.1	169.5	131.3
Share-based compensation expense included in net income attributable to Biogen Inc.
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 215.1	$ 204.1	$ 171.6

Share-Based Payments - Summary of Share-based Compensation Expense Associated with Each Share-based Compensating Programs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ (263.5)	$ (246.6)	$ (204.5)
Subtotal	273.6	258.8	211.3
Capitalized share-based compensation costs	(9.3)	(8.0)	(6.2)
Share-based compensation expense included in total cost and expense	264.3	250.8	205.1
Market stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	13.2	45.6	40.5
Time-vested restricted stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	202.3	159.8	142.6
Cash settled performance units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	0.0	0.0	(1.7)
Performance units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	0.0	0.0	(0.1)
Performance stock units settled in stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	35.0	23.9	7.9
Performance stock units settled in cash
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	10.1	12.2	8.6
Employee stock purchase plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	12.7	17.3	13.5
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 0.3	$ 0.0	$ 0.0

Share-Based Payments - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended	12 Months Ended
	Jun. 30, 2017 shares	Jun. 30, 2015 shares	May 31, 2006 shares	Mar. 31, 2018	Dec. 31, 2022 USD ($) plan Increment $ / shares shares	Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2013 Increment
Share-based Compensation Arrangement by Share-based Payment Award
Unrecognized compensation cost related to unvested share-based compensation					$ 290.5
Weighted-average period to recognize the cost of unvested awards					2 years
Number of share-based compensation plans pursuant to which awards are currently being made \| plan					3
Total intrinsic value of options exercised							$ 2.9
Shares issued under ESPP (in shares) \| shares		6,200,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Share based payment arrangement, term					10 years
Market Stock Units (MSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Number of equal annual increments \| Increment					3			4
Percentage of earnings of the target number of units granted based on actual stock performance					0.00%			0.00%
Percentage of earnings of the target number of units granted based on actual stock performance					200.00%			150.00%
Total fair value of vested awards					$ 18.8	$ 22.5	$ 26.9
Granted (in dollars per share) \| $ / shares					$ 0	$ 358.77	$ 398.61
Cash Settled Performance Units (CSPUs)
Share-based Compensation Arrangement by Share-based Payment Award
Number of equal annual increments \| Increment					3
Percentage of earnings of the target number of units granted based on actual stock performance					0.00%
Percentage of earnings of the target number of units granted based on actual stock performance					200.00%
Number of days for calculation of average closing stock price					30 days
Cash settlement of awards upon vesting							$ 3.8
Performance Units (PUs)
Share-based Compensation Arrangement by Share-based Payment Award
Number of equal annual increments \| Increment					3
Percentage of earnings of the target number of units granted based on actual stock performance					0.00%
Percentage of earnings of the target number of units granted based on actual stock performance					200.00%
Number of days for calculation of average closing stock price					30 days
Total fair value of vested awards					$ 9.5	$ 15.5
Cash settlement of awards upon vesting							3.4
Granted (in dollars per share) \| $ / shares					$ 294.43
PSUs Settled in Stock
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period				3 years
Percentage of earnings of the target number of units granted based on actual stock performance					0.00%
Percentage of earnings of the target number of units granted based on actual stock performance					200.00%
Granted (in dollars per share) \| $ / shares					$ 294.43
PSUs Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period				3 years
Percentage of earnings of the target number of units granted based on actual stock performance					0.00%
Percentage of earnings of the target number of units granted based on actual stock performance					200.00%
Number of days for calculation of average closing stock price					30 days
Total fair value of vested awards					$ 11.0	9.9
Time-Vested Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period					3 years
Total fair value of vested awards					$ 116.3	$ 132.2	$ 140.5
Granted (in dollars per share) \| $ / shares					$ 221.28	$ 276.90	$ 318.87
Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award
Total number of shares of common stock for issuance (in shares) \| shares			1,600,000
Ratio of total number of shares reserved under the plan			1.5
2017 Omnibus Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award
Ratio of total number of shares reserved under the plan	1.5
Omnibus Plan number of shares authorized (in shares) \| shares	8,000,000
2017 Omnibus Equity Plan \| Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award
Stock options granted (in shares) \| shares					81,000
Stock options granted, weighted average price (in dollars per share) \| $ / shares					$ 139.10
Stock options granted, grant date fair value					$ 11.2
Vesting period					3 years

Share-Based Payments - Tax Benefit and Cash Received from Stock Option Exercises (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Share-Based Payment Arrangement [Abstract]
Tax benefit realized for stock options	$ 2.9
Cash received from the exercise of stock options	$ 0.7

Share-Based Payments - Market Stock Units Activity (Details) - Market stock units - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Shares
Beginning balance, unvested (in shares)	257,000
Granted (in shares)	0
Vested (in shares)	(87,000)
Forfeited (in shares)	(57,000)
Ending balance, unvested shares (in shares)	113,000	257,000
Weighted Average Grant Date Fair Value
Beginning balance, unvested (in dollars per share)	$ 372.08
Granted (in dollars per share)	0	$ 358.77	$ 398.61
Vested (in dollars per share)	369.22
Forfeited (in dollars per share)	371.24
Ending balance, unvested (in dollars per share)	$ 366.52	$ 372.08

Share-Based Payments - Assumptions Used in Valuation of Market Based Stock Units (Details) - Market stock units - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award
Expected dividend yield		0.00%	0.00%
Minimum range of risk-free interest rates		0.06%	1.41%
Maximum range of risk-free interest rates		0.21%	1.48%
Average stock price on grant date minimum		$ 262.23	$ 257.83
Average stock price on grant date maximum		360.31	325.40
Granted (in dollars per share)	$ 0	$ 358.77	$ 398.61
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Range of expected stock price volatility		54.80%	37.80%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Range of expected stock price volatility		61.60%	44.10%

Share-Based Payments - Performance Stock Units Settled in Stock Activity (Details) - Performance stock units settled in stock shares in Thousands	12 Months Ended
	Dec. 31, 2022 $ / shares shares
Shares
Beginning balance, unvested (in shares) \| shares	196,000
Granted (in shares) \| shares	270,000
Vested (in shares) \| shares	(44,000)
Forfeited (in shares) \| shares	(86,000)
Ending balance, unvested shares (in shares) \| shares	336,000
Weighted Average Grant Date Fair Value
Beginning balance, unvested (in dollars per share) \| $ / shares	$ 289.94
Granted (in dollars per share) \| $ / shares	294.43
Vested (in dollars per share) \| $ / shares	316.83
Forfeited (in dollars per share) \| $ / shares	279.09
Ending balance, unvested (in dollars per share) \| $ / shares	$ 292.95

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

Share-Based Payments - Performance Stock Units Settled in Cash Activity (Details) - Performance stock units settled in cash shares in Thousands	12 Months Ended
	Dec. 31, 2022 shares
Shares
Beginning balance, unvested (in shares)	134,000
Granted (in shares)	24,000
Vested (in shares)	(49,000)
Forfeited (in shares)	(26,000)
Ending balance, unvested shares (in shares)	83,000

Share-Based Payments - Time-Vested Restricted Stock Units Activity (Details) - RSUs - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Shares
Beginning balance, unvested (in shares)	1,202,000
Granted (in shares)	1,751,000
Vested (in shares)	(539,000)
Forfeited (in shares)	(468,000)
Ending balance, unvested shares (in shares)	1,946,000	1,202,000
Weighted Average Grant Date Fair Value
Beginning balance, unvested (in dollars per share)	$ 291.54
Granted (in dollars per share)	221.28	$ 276.90	$ 318.87
Vested (in dollars per share)	297.72
Forfeited (in dollars per share)	244.03
Ending balance, unvested (in dollars per share)	$ 237.90	$ 291.54
Number of shares granted (in shares)	1,751,000
Director
Shares
Granted (in shares)	15,000
Weighted Average Grant Date Fair Value
Number of shares granted (in shares)	15,000

Share-Based Payments - Shares Issued Under Employee Stock Purchase Plan (Details) - USD ($) shares in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under the 2015 ESPP (in shares)	6,200
2015 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under the 2015 ESPP (in shares)		241	248	212
Cash received under the 2015 ESPP		$ 44.2	$ 54.4	$ 48.6

Income Taxes - Income Before Income Tax Provision and the Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income before income tax (benefit) expense:
Domestic	$ 1,842.0	$ 448.3	$ 3,290.0
Foreign	1,749.8	1,296.9	1,757.5
Income before income tax expense and equity in loss of investee, net of tax	3,591.8	1,745.2	5,047.5
Current:
Federal	694.5	319.1	647.0
State	39.0	23.1	41.2
Foreign	67.9	137.1	155.1
Total current	801.4	479.3	843.3
Deferred:
Federal	(328.3)	(242.5)	(1,749.9)
State	2.5	(11.9)	(6.8)
Foreign	157.2	(172.4)	1,905.7
Total deferred	(168.6)	(426.8)	149.0
Total income tax (benefit) expense	$ 632.8	$ 52.5	$ 992.3

Income Taxes - Narrative (Details) $ in Millions, ₩ in Billions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 KRW (₩)	Dec. 31, 2017	Feb. 29, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Tax Credit Carryforward [Line Items]
Income taxes paid	$ 137.8
Deferred tax liabilities, temporary differences, purchase accounting, foreign subsidiaries	1,500.0
Total deferred charges and prepaid taxes	56.6	$ 39.6
Deferred tax asset, net		100.0
Valuation allowance	2,003.3	1,961.3		$ 85.0
Unrecognized tax benefit	134.0	87.5	$ 68.8
Net interest expense	0.7	2.7	1.0
Unrecognized tax benefits, interest on income taxes accrued	25.2	24.8
Decrease in unrecognized tax benefits is reasonably possible	500.0
Samsung Bioepis
Tax Credit Carryforward [Line Items]
Investment in Samsung Bioepis		599.9			₩ 713.3		$ 45.0	₩ 49.5
2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax liabilities	558.0	633.0
Domestic Country
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	24.8
Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Increase in unrecognized tax benefit	450.0	455.0
General Business \| Domestic Country
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	8.1
Operating loss carryforward, subject to expiration	15,500.0
General Business \| Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Operating loss carryforward, subject to expiration	15,400.0
Research \| State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount	132.7
Earnings in the form of cash and cash equivalents \| 2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax repatriation tax rate						15.50%
Other Foreign Earnings \| 2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition toll tax repatriation tax rate						8.00%
Minimum
Tax Credit Carryforward [Line Items]
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting	300.0
Maximum
Tax Credit Carryforward [Line Items]
Residual U.S. tax liability on reversal of deferred tax liabilities on foreign subsidiaries purchase accounting	400.0
TECFIDERA
Tax Credit Carryforward [Line Items]
Deferred tax assets, value, reduction in value			1,700.0
Deferred tax liabilities, value, reduction in value			1,600.0
Income tax expense, reduction in deferred tax assets and liabilities, net			$ 90.3
Deferred tax assets, increase in value	17.4	108.5
Deferred tax liability, increase in value	$ 16.7	$ 103.9

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Tax credits	$ 112.6		$ 121.0
Inventory, other reserves and accruals	202.8		199.4
Intangibles, net	1,370.3		1,477.5
Neurimmune's tax basis in ADUHELM	470.3		475.8
IRC Section 174 capitalized research and development	271.8		0.0
Net operating loss	1,845.9		1,973.0
Share-based compensation	37.2		31.7
Other	280.7		208.8
Valuation allowance	(2,003.3)	$ (85.0)	(1,961.3)
Total deferred tax assets	2,588.3		2,525.9
Deferred tax liabilities:
Purchased intangible assets	(76.1)		(256.6)
Samsung Bioepis investment installments	(138.0)		0.0
GILTI	(1,002.0)		(1,037.6)
Tax credits	(228.7)		(260.2)
Depreciation, amortization and other	(251.8)		(250.9)
Total deferred tax liabilities	$ (1,696.6)		$ (1,805.3)

Income Taxes - Tax Rate (Details)	12 Months Ended
Income Taxes - Tax Rate (Details)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory rate	21.00%	21.00%	21.00%
State taxes	1.10%	0.80%	0.70%
Taxes on foreign earnings	(4.90%)	(10.50%)	(3.30%)
Tax credits	(1.70%)	(3.80%)	(1.20%)
Purchased intangible assets	0.30%	(1.60%)	0.70%
TECFIDERA impairment	0.00%	0.00%	1.80%
GILTI	0.70%	1.30%	1.30%
Sale of Samsung Bioepis	(1.60%)	0.00%	0.00%
Litigation settlement agreement	2.60%	0.00%	0.00%
Neurimmune tax impacts	2.30%	(5.30%)	(0.10%)
Internal reorganization	(1.40%)	0.00%	0.00%
Other	(0.80%)	1.10%	(1.20%)
Effective tax rate	17.60%	3.00%	19.70%

Income Taxes - Accounting for Uncertainty in Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 563.4	$ 75.7	$ 129.9
Additions based on tax positions related to the current period	36.3	4.2	1.5
Additions for tax positions of prior periods	23.4	509.9	51.7
Reductions for tax positions of prior periods	(14.9)	(18.8)	(63.6)
Statute expirations	(1.6)	(3.2)	(7.9)
Settlement payment	(0.2)	(4.4)	(35.9)
Ending balance	$ 606.4	$ 563.4	$ 75.7

Other Consolidated Financial Statement Detail - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interest	$ 262.5	$ 280.8	$ 272.7
Income taxes	$ 932.9	$ 247.9	$ 906.7

Other Consolidated Financial Statement Detail - Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Mar. 31, 2022	Feb. 29, 2012
Collaborative arrangements and non-collaborative arrangement transactions
Gain on sale of equity interest in Samsung Bioepis		$ (1,505.4)	$ 0.0	$ 0.0
Litigation settlement agreement and settlement fees	$ 900.0	917.0	0.0	0.0
Interest income		(89.3)	(11.0)	(42.0)
Interest expense		246.6	253.6	222.5
(Gains) losses on investments, net		277.3	824.9	(685.7)
Foreign exchange (gains) losses, net		35.5	22.4	10.7
Other, net		10.1	5.6	(2.9)
Other (income) expense		$ (108.2)	$ 1,095.5	$ (497.4)
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Ownership percentage					49.90%	15.00%

Other Consolidated Financial Statement Detail - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Unrealized (gains) losses recognized on equity securities	$ 264.7	$ 831.4	$ (681.8)
Other long-term liabilities	944.2	1,320.5
Accrued income taxes	541.7	664.5
Denali, Ionis, Sage, and Sangamo
Business Acquisition [Line Items]
Unrealized (gains) losses recognized on equity securities	$ (278.0)	$ (819.6)

Other Consolidated Financial Statement Detail - Gain (Loss) on Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net (gains) losses recognized on equity securities	$ 264.7	$ 821.1	$ (693.9)
Less: Net (gains) losses realized on equity securities	0.0	(10.3)	(12.1)
Unrealized (gains) losses recognized on equity securities	$ 264.7	$ 831.4	$ (681.8)

Other Consolidated Financial Statement Detail - Accrued Expense and Other (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	$ 1,035.0	$ 935.3	$ 1,276.0	$ 1,198.9
Total accrued expense and other	2,521.4	2,535.2
Component of accrued expense and other
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Revenue-related reserves for discounts and allowances	891.6	802.1
Employee compensation and benefits	395.6	345.1
Collaboration expense	277.9	324.7
Royalties and licensing fees	209.4	234.7
Other	$ 746.9	$ 828.6

Collaborative and Other Relationships - OCREVUS (Details) - OCREVUS $ in Millions	1 Months Ended
	Mar. 31, 2017 USD ($)
Collaborative arrangements and non-collaborative arrangement transactions
Royalty operating profit threshold for highest royalty rate percentage	$ 900.0
Reduction in royalty rate	50.00%
Collaboration agreement term	11 years
Foreign Tax Authority
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	3.00%
Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	13.50%
Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Royalty percentage to be received	24.00%

Collaborative and Other Relationships - Mosunetuzumab (Details) - Mosunetuzumab - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Option exercise fee	$ 30.0
Development of product candidate expense			$ 20.0
Percentage of future development costs		30.00%	30.00%
Research and development expense asset acquired		$ 28.4
Sales and marketing expense		$ 13.0

Collaborative and Other Relationships - Co-promotion Profit Sharing Formula (Details) - RITUXAN	Dec. 31, 2022
Collaborative arrangements and non-collaborative arrangement transactions
After LUNSUMIO Approval until the First Threshold Date	37.50%
After First Threshold Date until the Second Threshold Date	35.00%
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Four	30.00%

Collaborative and Other Relationships - Profit Sharing (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
RITUXAN
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of co promotion operating profits first fifty million	30.00%
Until Second GAZYVA Threshold Date	37.50%
GAZYVA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of co promotion operating profits first fifty million	35.00%
Co-promotion operating profit threshold for Rituxan in US and Canada to determine share of co promotion operating profit prior to amendment	$ 50.0
Limit of gross sale of GAZYVA to be achieved in preceding 12 months under option one	500.0
Limit of gross sale of GAZYVA to be achieved in any 12 months under option one	150.0
Sales trigger gross sales threshold	$ 350.0
Until Second GAZYVA Threshold Date	37.50%	37.50%	37.50%
New Anti Cd20
Collaborative arrangements and non-collaborative arrangement transactions
Future percentage of co-promotion operating profits	37.50%	37.50%	37.50%

Collaborative and Other Relationships - Pretax Profit Sharing Formula (Details) - GAZYVA	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Until Second GAZYVA Threshold Date	37.50%	37.50%	37.50%
After Second GAZYVA Threshold Date	35.00%

Collaborative and Other Relationships - Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Revenue	$ 10,173.4	$ 10,981.7	$ 13,444.6
Revenue from anti-CD20 therapeutic programs
Collaborative arrangements and non-collaborative arrangement transactions
Revenue	1,700.5	1,658.5	1,977.8
Genentech
Collaborative arrangements and non-collaborative arrangement transactions
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA	547.0	647.7	1,080.2
Royalty revenue on sales of OCREVUS	$ 17.2	$ 19.1	$ 52.2

- Definition

+ References

+ Details

Collaborative and Other Relationships - Ionis (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended					12 Months Ended
	Dec. 31, 2019	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2016	Dec. 31, 2018
Collaborative arrangements and non-collaborative arrangement transactions
Cost of sales, excluding amortization and impairment of acquired intangible assets						$ 2,278.3	$ 2,109.7	$ 1,805.2
Research and development						2,231.1	2,501.2	3,990.9
Ionis Pharmaceuticals
Collaborative arrangements and non-collaborative arrangement transactions
License fee				$ 70.0	$ 70.0
Expected license fee and regulatory milestone payments				$ 130.0	$ 130.0
Research and development expense asset acquired	$ 45.0
Additional milestone payment	155.0
Term of collaboration agreement		10 years		6 years
Total payment to enter collaboration agreement		$ 1,000.0
Upfront payment for collaboration agreement		375.0
Purchase of common stock		$ 625.0
Investment in common stock, shares purchased (in shares)		11.5
Prepaid research and discovery services		$ 50.9
Research and development		324.1				10.0	22.5	11.3
Estimated additional payments upon achievement of development and commercial milestones			$ 260.0
Upfront and milestone payments made to collaborative partner			25.0
Expected additional milestone payments when certain sales threshold is met			$ 800.0
Ionis Pharmaceuticals \| SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Cost of sales, excluding amortization and impairment of acquired intangible assets						243.1	267.1	286.6
Ionis Pharmaceuticals \| BIIB115
Collaborative arrangements and non-collaborative arrangement transactions
Upfront payment for collaboration agreement							60.0
Ionis Pharmaceuticals \| SOD1
Collaborative arrangements and non-collaborative arrangement transactions
Research and development						$ 17.0	$ 10.0	$ 28.0
Estimated additional payments upon achievement of development and commercial milestones										$ 55.0
Ionis Pharmaceuticals \| BIIB080
Collaborative arrangements and non-collaborative arrangement transactions
Research and development expense asset acquired	$ 10.0
Ionis Pharmaceuticals \| Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Estimated additional payments upon achievement of development and commercial milestones		125.0
Ionis Pharmaceuticals \| Minimum \| SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration						11.00%			11.00%
Ionis Pharmaceuticals \| Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Estimated additional payments upon achievement of development and commercial milestones		$ 270.0
Ionis Pharmaceuticals \| Maximum \| SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration						15.00%			15.00%

Collaborative and Other Relationships - Eisai (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments		$ 2.6	$ 34.9	$ 3.3
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Related cost-sharing reduction (as a percentage)		80.00%
Income (loss) from equity method investments	$ 33.8	$ 0.0	45.0	33.8
Additional milestone payment		$ 0.0	$ 100.0	$ 75.0

Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 347.2	$ 323.0	$ 219.3
Expense reflected within statements of income	173.6	161.5	109.6
Selling, general and administrative \| E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	52.3	13.6	4.9
Expense incurred by the collaboration	$ 104.6	$ 27.2	$ 9.8

Collaborative and Other Relationships - ADUHELM Collaboration Agreement (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments					$ 2.6	$ 34.9	$ 3.3
Royalty cost of sales					2,278.3	2,109.7	1,805.2
Regulatory Milestones \| Neurimmune
Collaborative arrangements and non-collaborative arrangement transactions
Upfront and milestone payments made to collaborative partner						100.0	75.0
ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Research and development expense asset acquired					335.0
Income (loss) from equity method investments					111.0	30.0
Royalty cost of sales	$ 164.0	$ 275.0
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Additional milestone payment					0.0	100.0	75.0
Income (loss) from equity method investments				$ 33.8	0.0	45.0	33.8
Amounts receivable	88.0				88.0	285.4
Amounts payable	$ 81.2				$ 81.2	46.5
Eisai \| Milestone Payments
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of future development costs					45.00%
Eisai \| Collaboration profit sharing
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense					$ 224.7	233.2
Eisai \| ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments			$ 45.0			59.0
Eisai \| ADUHELM \| Milestone Payments
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense						45.0	$ 33.8
Eisai \| ADUHELM \| Inventory, Idle Capacity Charges And Contractual Commitments
Collaborative arrangements and non-collaborative arrangement transactions
Recognized net reductions to operating expense					$ 197.0	$ 99.0

Collaborative and Other Relationships - Summary of Activity Related to Aducanumab Collaboration (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit (loss) sharing in our consolidated statements of income		$ 2.6	$ 34.9	$ 3.3
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income		173.6	161.5	109.6
Total ADUHELM Collaboration third party milestones		0.0	100.0	75.0
Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit (loss) sharing in our consolidated statements of income	$ 33.8	0.0	45.0	33.8
Aducanumab \| Research and development \| Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration		149.4	183.7	152.0
Expense reflected within statements of income		82.2	101.1	83.6
Aducanumab \| Selling, general and administrative \| Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration		134.2	562.3	353.0
Expense reflected within statements of income		$ 71.5	$ 301.4	$ 193.7

Collaborative and Other Relationships - Summary of Activity Related to the UCB Collaboration (Details) - Research and development - UCB Pharma S.A. - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 68.0	$ 84.2	$ 58.3
Expense reflected within statements of income	$ 34.0	$ 42.1	$ 29.2

Collaborative and Other Relationships - Alkermes (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Inventory and purchase commitment charges		$ 2,278.3	$ 2,109.7	$ 1,805.2
Potential future milestone payments commitment to third party approximately		9,300.0
Research and development		$ 2,231.1	2,501.2	3,990.9
VUMERITY \| Alkermes
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration	15.00%	15.00%
Royalties payable period, post FDA approval	5 years
Inventory and purchase commitment charges		$ 83.0	$ 61.6	$ 12.9

Collaborative and Other Relationships - Acorda (Details) - Acorda - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Expected additional milestone payments when certain sales threshold is met	$ 15.0
Foreign sales required to trigger milestone	$ 100.0
Expense reflected within statements of income		$ 46.1	$ 46.6	$ 44.5

Collaborative and Other Relationships - Other Arrangements (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended					12 Months Ended
	Aug. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Apr. 30, 2020	Feb. 29, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2023
Collaborative arrangements and non-collaborative arrangement transactions
Potential future milestone payments commitment to third party approximately						$ 9,300.0
Research and development						2,231.1	$ 2,501.2	$ 3,990.9
Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Global licensing collaboration, shares purchased, amount		$ 650.0
Global licensing collaboration, shares purchased (in shares)		6.2
Global licensing collaboration, purchase price per share (in dollars per share)		$ 104.14
Research and development expense asset acquired		$ 209.0
Upfront and milestone payments made to collaborative partner		875.0
Global licensing collaboration, development and commercial milestone payments		$ 1,600.0
Sage Therapeutics \| Forecast
Collaborative arrangements and non-collaborative arrangement transactions
Potential future milestone payments commitment to third party approximately									$ 225.0
Denali Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Global licensing collaboration, shares purchased, amount			$ 465.0
Global licensing collaboration, shares purchased (in shares)			13.0
Global licensing collaboration, purchase price per share (in dollars per share)			$ 34.94
Research and development expense asset acquired			$ 41.3
Upfront and milestone payments made to collaborative partner			560.0
Global licensing collaboration, development and commercial milestone payments			$ 1,100.0
Sangamo Therapeutics, Inc. Agreement
Collaborative arrangements and non-collaborative arrangement transactions
Global licensing collaboration, shares purchased, amount				$ 225.0
Global licensing collaboration, shares purchased (in shares)				24.0
Global licensing collaboration, purchase price per share (in dollars per share)				$ 9.21
Research and development expense asset acquired					$ 83.0
Upfront and milestone payments made to collaborative partner					125.0
Global licensing collaboration, development and commercial milestone payments					$ 2,400.0
Term of collaboration agreement					5 years
Global licensing collaboration, payment, selection of targets					$ 80.0
Global licensing collaboration, payment, first milestone					1,900.0
Global licensing collaboration, payment, sales based milestone					$ 380.0
Other research and discovery
Collaborative arrangements and non-collaborative arrangement transactions
Research and development						$ 39.2	$ 89.1	$ 92.1
InnoCare Pharma Limited (InnoCare) Agreement
Collaborative arrangements and non-collaborative arrangement transactions
Upfront and milestone payments made to collaborative partner	$ 125.0
Contingent milestone payments made to collaborative partner	$ 812.5

Collaborative and Other Relationships - Summary of Activity Related to Sage Therapeutics (Details) - Sage Therapeutics - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Research and development
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 173.3	$ 167.7	$ 0.0
Expense reflected within statements of income	86.7	83.8	0.0
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	109.9	36.4	0.0
Expense reflected within statements of income	$ 55.0	$ 18.2	$ 0.0

Collaborative and Other Relationships - Summary of Activity Related To Denali Therapeutics (Details) - Research and development - Denali Therapeutics - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 75.1	$ 42.5	$ 14.6
Expense reflected within statements of income	$ 43.8	$ 25.5	$ 8.8

Collaborative and Other Relationships - Summary of Activity Related to Sangamo Therapeutics (Details) - Research and development - Sangamo Therapeutics, Inc. Agreement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 19.1	$ 22.7	$ 10.1
Expense reflected within statements of income	$ 12.1	$ 14.6	$ 6.4

Collaborative and Other Relationships - Samsung Bioepis (Details) ₩ in Millions, $ in Millions	1 Months Ended										3 Months Ended	12 Months Ended
	Apr. 30, 2022 USD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Nov. 30, 2018 KRW (₩)	Aug. 31, 2017 USD ($)	May 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Dec. 31, 2013 USD ($)	Feb. 29, 2012 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) product	Mar. 31, 2022 KRW (₩)	Dec. 31, 2021 KRW (₩)	May 31, 2018	Feb. 29, 2012 KRW (₩)
Collaborative arrangements and non-collaborative arrangement transactions
Income (loss) from equity method investments												$ 2.6	$ 34.9	$ 3.3
Income tax (benefit) expense												632.8	52.5	992.3
Number of ophthalmolgy biosimilar products \| product															2
Research and development												2,231.1	2,501.2	3,990.9
Collaboration profit (loss) sharing												(7.4)	7.2	232.9
Revenue												10,173.4	10,981.7	13,444.6
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Investment in Samsung Bioepis \| ₩																₩ 581.6
Proceeds from divestiture of interest in joint venture	$ 1,000.0
Due from joint venture	1,300.0
Upfront and milestone payments made to collaborative partner		$ 100.0
Research and development expense asset acquired															$ 63.0
Prepaid research and discovery services			$ 37.0												$ 37.0
Additional milestone payment	50.0
Accrued milestone payment											$ 15.0
Estimated additional payments upon achievement of development and commercial milestones												180.0
Term of collaboration agreement									10 years
Option exercise fee												$ 60.0
Research and development									$ 46.0
Expected profit share percentage			45.00%									50.00%
Collaboration profit (loss) sharing												$ 217.4	285.4	266.5
Revenue												$ 20.6	20.7	$ 20.9
Term of collaboration agreement, additional length									5 years			5 years
Amounts receivable												$ 2.0	4.1
Amounts payable												40.5	148.7
Samsung Bioepis \| Payment Due At First Anniversary
Collaborative arrangements and non-collaborative arrangement transactions
Due from joint venture	812.5
Samsung Bioepis \| Payment Due At Second Anniversary
Collaborative arrangements and non-collaborative arrangement transactions
Due from joint venture	437.5
Samsung Bioepis \| Development Milestones
Collaborative arrangements and non-collaborative arrangement transactions
Additional milestone payment											$ 15.0
Samsung Bioepis
Collaborative arrangements and non-collaborative arrangement transactions
Contributions by third party										$ 250.0									₩ 280,500.0
Joint venture ownership percentage										85.00%
Investment in Samsung Bioepis										$ 45.0			599.9				₩ 713,300.0		₩ 49,500.0
Ownership percentage										15.00%						49.90%			15.00%
Ownership percentage before additional purchase transaction																		5.00%
Payments to increase investment in Samsung Bioepis				$ 676.6	₩ 759,500.0
Total basis difference	$ 675.0
Net profits on investment												2.6	34.9
Income (loss) from equity method investments												17.0	64.6
Amortization												$ 14.4	29.7
Income tax (benefit) expense													$ 31.2
Additional milestone payment									$ 25.0
Net change in acquired and in-licensed rights and patents						$ 75.0	$ 75.0	$ 75.0
Samsung Bioepis \| Inventories
Collaborative arrangements and non-collaborative arrangement transactions
Equity method investment basis difference amortization period	1 year 6 months
Samsung Bioepis \| Completed technology
Collaborative arrangements and non-collaborative arrangement transactions
Equity method investment basis difference amortization period	15 years

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Mar. 31, 2022
Variable Interest Entity [Line Items]
Potential future milestone payments commitment to third party approximately			$ 9,300.0
Income (loss) from equity method investments			2.6	$ 34.9	$ 3.3
Deferred tax asset, net				100.0
Valuation allowance			2,003.3	1,961.3		$ 85.0
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities			27.8	24.6
ADUHELM
Variable Interest Entity [Line Items]
Income (loss) from equity method investments			$ 111.0	30.0
Neurimmune
Variable Interest Entity [Line Items]
Term of collaboration agreement			12 years
Research and development costs, percentage			100.00%
Regulatory Milestones
Variable Interest Entity [Line Items]
Potential future milestone payments commitment to third party approximately			$ 500.0
Regulatory Milestones \| Neurimmune
Variable Interest Entity [Line Items]
Potential future milestone payments commitment to third party approximately		$ 75.0
Eisai
Variable Interest Entity [Line Items]
Income (loss) from equity method investments		$ 33.8	$ 0.0	45.0	$ 33.8
Eisai \| ADUHELM
Variable Interest Entity [Line Items]
Income (loss) from equity method investments	$ 45.0			$ 59.0
Eisai \| Regulatory Milestones \| Neurimmune \| ADUHELM
Variable Interest Entity [Line Items]
Potential future milestone payments commitment to third party approximately	$ 100.0

Litigation (Details) $ in Millions	2 Months Ended
Litigation (Details) $ in Millions	Dec. 31, 2019 USD ($)
Loss Contingency, Information about Litigation Matters [Abstract]
Claims asserted	$ 200.0

Commitments and Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2022	Dec. 31, 2016	Dec. 31, 2023	Dec. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2013
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		$ 9,300.0
Accrued expenses		20.4
Cancellable future commitments		929.0
Liabilities associated with uncertain tax positions		154.6
Income taxes paid		137.8
2017 Tax Act
Business Acquisition [Line Items]
Transition toll tax liabilities		558.0			$ 633.0
Development Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		2,000.0
Regulatory Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		500.0
Regulatory Milestones \| Neurimmune
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately							$ 75.0
Commercial Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		$ 6,800.0
Ionis Pharmaceuticals \| Minimum \| SPINRAZA
Business Acquisition [Line Items]
Percentage of royalties as per collaboration		11.00%	11.00%
Ionis Pharmaceuticals \| Maximum \| SPINRAZA
Business Acquisition [Line Items]
Percentage of royalties as per collaboration		15.00%	15.00%
Alkermes \| VUMERITY
Business Acquisition [Line Items]
Percentage of royalties as per collaboration	15.00%	15.00%
Royalties payable period, post FDA approval	5 years
Aducanumab \| Forecast
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately				$ 356.2
Eisai \| ADUHELM \| Regulatory Milestones \| Neurimmune
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately						$ 100.0
TYSABRI
Business Acquisition [Line Items]
Future contingent payment for annual worldwide net sales up to threshold, percentage								18.00%
Future contingent payment threshold								$ 2,000.0
Future contingent payment for annual worldwide net sales that exceeding threshold, percentage								25.00%

Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
Employee Benefit Plans (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Germany
Defined Contribution Plan Disclosure [Line Items]
Employee benefit plan obligations	$ 40.9	$ 68.4
Periodic pension cost	5.9	7.6	$ 6.2
Germany \| Other (income) expense, net
Defined Contribution Plan Disclosure [Line Items]
Periodic pension cost	1.8	2.1	2.0
Switzerland
Defined Contribution Plan Disclosure [Line Items]
Unfunded net pension	49.9	64.1
Employee benefit plan obligations	193.7	200.1
Pension cost (reversal)	$ 20.0	$ 21.5	$ 15.5
Percentage Of Minimum Investment Return	2.00%	1.00%	1.00%
Switzerland \| Other (income) expense, net
Defined Contribution Plan Disclosure [Line Items]
Pension cost (reversal)	$ 5.3	$ 3.5	$ 2.6
United States
Defined Contribution Plan Disclosure [Line Items]
Minimum qualifying age for employee benefit plan	21 years
Expenses related to savings plan	$ 56.0	58.4	$ 44.3
Deferred Compensation Plan
Defined Contribution Plan Disclosure [Line Items]
Deferred compensation liability	$ 131.9	$ 131.4

Segment Information - Narrative (Details) $ in Millions	12 Months Ended
Segment Information - Narrative (Details) $ in Millions	Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Revenue from External Customer [Line Items]
Number of reportable segment \| segment	1
Other long-lived assets	$ 3,702.5	$ 3,791.8	$ 3,844.8
Solothurn, Switzerland
Revenue from External Customer [Line Items]
Other long-lived assets	$ 2,198.5	$ 2,237.0	$ 2,180.6

Segment Information - Geographic Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue, Major Customer [Line Items]
Revenue	$ 10,173.4	$ 10,981.7	$ 13,444.6
Long-lived assets	3,702.5	3,791.8	3,844.8
U.S.
Revenue, Major Customer [Line Items]
Long-lived assets	1,369.4	1,390.5	1,496.3
Europe
Revenue, Major Customer [Line Items]
Long-lived assets	2,275.8	2,337.8	2,290.2
Germany
Revenue, Major Customer [Line Items]
Long-lived assets	21.0	25.4	31.2
Asia
Revenue, Major Customer [Line Items]
Long-lived assets	13.7	16.4	16.2
Other
Revenue, Major Customer [Line Items]
Long-lived assets	22.6	21.7	10.9
Product, net
Revenue, Major Customer [Line Items]
Revenue	7,987.8	8,846.9	10,692.2
Product, net \| U.S.
Revenue, Major Customer [Line Items]
Revenue	3,469.3	3,805.7	5,900.1
Product, net \| Europe
Revenue, Major Customer [Line Items]
Revenue	2,401.3	2,626.0	2,495.3
Product, net \| Germany
Revenue, Major Customer [Line Items]
Revenue	926.2	1,162.4	1,161.1
Product, net \| Asia
Revenue, Major Customer [Line Items]
Revenue	672.1	688.0	596.7
Product, net \| Other
Revenue, Major Customer [Line Items]
Revenue	518.9	564.8	539.0
Revenue from anti-CD20 therapeutic programs
Revenue, Major Customer [Line Items]
Revenue	1,700.5	1,658.5	1,977.8
Revenue from anti-CD20 therapeutic programs \| U.S.
Revenue, Major Customer [Line Items]
Revenue	1,636.4	1,596.7	1,897.4
Revenue from anti-CD20 therapeutic programs \| Europe
Revenue, Major Customer [Line Items]
Revenue	0.1	0.0	0.1
Revenue from anti-CD20 therapeutic programs \| Germany
Revenue, Major Customer [Line Items]
Revenue	0.0	0.0	0.0
Revenue from anti-CD20 therapeutic programs \| Asia
Revenue, Major Customer [Line Items]
Revenue	0.0	0.0	0.0
Revenue from anti-CD20 therapeutic programs \| Other
Revenue, Major Customer [Line Items]
Revenue	64.0	61.8	80.3
Other
Revenue, Major Customer [Line Items]
Revenue	485.1	476.3	774.6
Other \| U.S.
Revenue, Major Customer [Line Items]
Revenue	425.8	429.9	733.6
Other \| Europe
Revenue, Major Customer [Line Items]
Revenue	11.7	9.7	8.0
Other \| Germany
Revenue, Major Customer [Line Items]
Revenue	0.0	0.0	0.1
Other \| Asia
Revenue, Major Customer [Line Items]
Revenue	47.6	36.7	32.9
Other \| Other
Revenue, Major Customer [Line Items]
Revenue	$ 0.0	$ 0.0	$ 0.0