0000875045-20-000005 | 10-K | XBRL Viewer

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

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

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total Revenues	$ 14,377.9	$ 13,452.9	$ 12,273.9
Cost and expenses:
Cost of sales, excluding amortization and impairment of acquired intangible assets	1,955.4	1,816.3	1,630.0
Research and development	2,280.6	2,597.2	2,253.6
Selling, general and administrative	2,374.7	2,106.3	1,933.9
Amortization and impairment of acquired intangible assets	489.9	747.3	814.7
Collaboration profit (loss) sharing	241.6	185.0	112.3
Loss on divestiture of Hillerød, Denmark manufacturing operations	55.3	0.0	0.0
Acquired in-process research and development	0.0	112.5	120.0
(Gain) loss on fair value remeasurement of contingent consideration	(63.7)	(12.3)	62.7
Restructuring Charges	1.5	12.0	0.9
Total cost and expenses	7,335.3	7,564.3	6,928.1
Income from operations	7,042.6	5,888.6	5,345.8
Other income (expense), net	83.3	11.0	(217.0)
Income before income tax expense and equity in loss of investee, net of tax	7,125.9	5,899.6	5,128.8
Income tax expense	1,158.0	1,425.6	2,458.7
Equity in loss of investee, net of tax	79.4	0.0	0.0
Net income	5,888.5	4,474.0	2,670.1
Net income (loss) attributable to noncontrolling interests, net of tax	0.0	43.3	131.0
Net income attributable to Biogen Inc.	$ 5,888.5	$ 4,430.7	$ 2,539.1
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 31.47	$ 21.63	$ 11.94
Diluted earnings per share attributable to Biogen Inc.	$ 31.42	$ 21.58	$ 11.92
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	187.1	204.9	212.6
Diluted earnings per share attributable to Biogen Inc.	187.4	205.3	213.0
Product, net
Total Revenues	$ 11,379.8	$ 10,886.8	$ 10,354.7
Revenues from anti-cd20 therapeutic programs
Total Revenues	2,290.4	1,980.2	1,559.2
Other revenue
Total Revenues	$ 707.7	$ 585.9	$ 360.0

Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Common stock, par value	$ 0.0005	$ 0.0005
Treasury stock at cost, shares	23.8	23.8

Other Consolidated Financial Statement Detail (Tables)

12 Months Ended

Dec. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Supplemental cash flow information

Supplemental disclosure of cash flow information for the years ended December 31, 2019, 2018 and 2017, is as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Cash paid during the year for:
Interest	$	244.2	$	243.2	$	281.7
Income taxes	$	1,064.5	$	1,007.1	$	1,066.4

Other income (expense), net

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



	For the Years Ended December 31,
(In millions)	2019			2018			2017
Interest income	$	120.0		$	112.5		$	78.5
Interest expense	(187.4		)	(200.6		)	(250.8		)
Gain (loss) on investments, net	204.7			119.5			(36.3		)
Foreign exchange gains (losses), net	(7.0		)	(9.9		)	6.3
Other, net	(47.0		)	(10.5		)	(14.7		)
Total other income (expense), net	$	83.3		$	11.0		$	(217.0	)

Gain (loss) on investments

The following table summarizes our gain (loss) on investments, net that relates to our equity securities held as of December 31, 2019, 2018 and 2017:



	For the Years Ended December 31,
(In millions)	2019		2018			2017
Net gains (losses) recognized during the period on equity securities	$	200.1	$	127.9		$	(19.8	)
Less: Net gains (losses) recognized during the period on equity securities sold during the period	$	50.0	$	(0.6	)	$	—
Unrealized gains (losses) recognized during the period on equity securities held as of December 31	$	150.1	$	128.5		$	(19.8	)

Accrued expenses and other

Accrued expenses and other consists of the following:



	As of December 31,
(In millions)	2019		2018
Revenue-related reserves for discounts and allowances	$	1,001.1	$	874.7
Employee compensation and benefits	309.1		320.9
Collaboration expenses	281.6		261.6
Royalties and licensing fees	220.9		224.7
Current portion of contingent consideration obligations	148.4		444.8
Construction in progress	78.0		125.2
Other	726.7		609.3
Total accrued expenses and other	$	2,765.8	$	2,861.2

Fair Value Measurements (Details 2) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Fair Value Measurements (Details 2) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition, Contingent Consideration [Line Items]
Loss (gain) on fair value remeasurement of contingent consideration	$ (2.6)	$ 57.8	$ 20.0	$ (11.5)	$ (79.3)	$ 87.9	$ (1.9)	$ 5.6	$ 63.7	$ 12.3	$ (62.7)
Payments									0.0	(101.5)
Fair Value, Measurements, Recurring
Business Acquisition, Contingent Consideration [Line Items]
Fair value, beginning of period				$ 409.8				$ 523.6	409.8	523.6
Fair value, end of period	$ 346.1				$ 409.8				$ 346.1	$ 409.8	$ 523.6

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

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

Business Overview

Biogen is a global biopharmaceutical company focused on discovering, developing and delivering worldwide innovative therapies for people living with serious neurological and neurodegenerative diseases as well as related therapeutic adjacencies. Our core growth areas include multiple sclerosis (MS) and neuroimmunology; Alzheimer’s disease (AD) and dementia; neuromuscular disorders, including spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS); movement disorders, including Parkinson's disease; and ophthalmology. We are also focused on discovering, developing and delivering worldwide innovative therapies in our emerging growth areas of immunology; neurocognitive disorders; acute neurology; and pain. In addition, we commercialize biosimilars of advanced biologics. We support our drug discovery and development efforts through the commitment of significant resources to discovery, research and development programs and business development opportunities.

Our marketed products include TECFIDERA, AVONEX, PLEGRIDY, TYSABRI, VUMERITY and FAMPYRA for the treatment of MS; SPINRAZA for the treatment of SMA; and FUMADERM for the treatment of severe plaque psoriasis. We also 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); and other potential anti-CD20 therapies pursuant to our collaboration arrangements with Genentech, Inc. (Genentech), a wholly-owned member of the Roche Group. For additional information on our collaboration arrangements with Genentech, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Our innovative drug development and commercialization activities are complemented by our biosimilar business that expands access to medicines and reduce the cost burden for healthcare systems. Through Samsung Bioepis Co., Ltd. (Samsung Bioepis), our joint venture with Samsung BioLogics Co., Ltd. (Samsung BioLogics), we market and sell BENEPALI, an etanercept biosimilar referencing ENBREL, IMRALDI, an adalimumab biosimilar referencing HUMIRA, and FLIXABI, an infliximab biosimilar referencing REMICADE, in certain countries in Europe and have exclusive rights to commercialize these products in China. Additionally, we have exclusive rights to commercialize two potential ophthalmology biosimilar products, SB11 referencing LUCENTIS and SB15 referencing EYLEA, in major markets worldwide, including the U.S., Canada, Europe, Japan and Australia. For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Consolidation

Our consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and those of certain variable interest entities where we are the primary beneficiary. For consolidated entities where we own or are exposed to less than 100% of the economics, we record net income (loss) attributable to noncontrolling interests 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. These considerations impact the way we account for our existing collaborative relationships and other arrangements. 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, revenues and expenses and related disclosure of contingent assets and liabilities. On an ongoing basis we evaluate our estimates, judgments and methodologies. 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 revenues and expenses. Actual results may differ from these estimates.

Revenue Recognition

In May 2014 the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry specific guidance. This standard requires a company to recognize revenues when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. This standard became effective for us on January 1, 2018, and was adopted using the modified retrospective method. The adoption of this standard as of January 1, 2018, did not change our revenue recognition.

We recognize revenues 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 revenues following the five-step model prescribed under the 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 revenues when (or as) we satisfy the performance obligation.

Product Revenues

In the United States (U.S.), we sell our products primarily to wholesale distributors and specialty pharmacy providers. 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 revenues are 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 revenues are 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. Our process for estimating reserves established for these variable consideration components do not differ materially from our historical practices.

Product revenue reserves, which are classified as a reduction in product revenues, 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 revenues 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, 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 other current liabilities. 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 in product revenue and 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 chargebacks consist of amounts that we expect to issue 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 expenses and other current liabilities. 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 customer’s buying 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.


•	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 returns are established for returns expected to be made by wholesalers and are recorded in the period the related revenue is recognized, resulting in a reduction to product revenues. 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 revenues. To the extent we can demonstrate a

separable benefit and fair value for these services we classify these payments in selling, general and administrative expenses.

Revenues 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 revenues 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, revenues are recognized as the underlying sales occur.

Revenues from anti-CD20 therapeutic programs consist of:


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


(ii)	other revenues from anti-CD20 therapeutic programs, which primarily consist of our share of pre-tax co-promotion profits on RITUXAN in Canada and royalty revenues on sales of OCREVUS.

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

For additional information on our relationship with Genentech, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Other Revenues

Royalty Revenues

We receive royalty revenues on sales by our licensees of products covered under patents that we own. We do not have future performance obligations under these license arrangements. We record these revenues based on estimates of the sales that occurred during the relevant period as a component of other revenues. The relevant period estimates of sales are based on interim data provided by licensees and other third parties and analysis of historical royalties that have been paid to us, adjusted for any changes in facts and circumstances, as appropriate. Differences between actual and estimated royalty revenues are adjusted for in the period in which they become known, typically the following quarter. Historically, adjustments have not been material when compared to actual amounts paid by licensees.

Collaborative and Other Relationships

We have a number of significant collaborative and other third-party relationships for revenues 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 revenues, cost of sales and operating expenses 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, we record our share of the revenues, cost of sales and operating expenses on a net basis in collaborative and other relationships included in other revenues in our consolidated statements of income.

Our development and commercialization arrangements with Genentech 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. Therefore, revenues relating to royalties or profit-sharing amounts received are recognized as the underlying sales occur.

For additional information on our collaboration arrangements with Genentech and Samsung Bioepis, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Other Corporate Revenues

We record other corporate revenues primarily from amounts earned under contract manufacturing agreements. Revenues under contract manufacturing agreements are 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.

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 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, 2019 and 2018.

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 expenses 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, 2019 and 2018, cash equivalents were comprised of money market funds, commercial paper, overnight reverse repurchase agreements and other debt securities with maturities less than 90 days 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.

In countries where we have experienced a pattern of payments extending beyond our contractual payment term and we expect to collect receivables greater than one year from the time of sale, we have assessed whether the customer has a significant financing component and discounted our receivables and reduced related revenues over the period of time that we estimate those amounts will be paid using the country’s market-based borrowing rate for such period. The related receivables are classified at the time of sale as non-current assets. We accrete interest

income on these receivables, which is recorded as a component of other income (expense), net in our consolidated statements of income.

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.

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, beginning January 1, 2018, unrealized gains and losses are included in other income (expense), net in our consolidated statements of income. Prior to January 1, 2018, unrealized gains and losses were included in accumulated other comprehensive income (loss) in equity, net of related tax effects. 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, beginning January 1, 2018, unrealized gains and losses are included in other income (expense), net in our consolidated statements of income. Prior to January 1, 2018, these investments were accounted for under the cost method of accounting. 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 changes in observable prices, 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.

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 a change in such judgment, 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.

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

In February 2016 the FASB issued ASU No. 2016-02, Leases (Topic 842), a new standard issued to increase transparency and comparability among organizations related to their leasing activities. This standard established a right-of-use model that requires all lessees to recognize right-of-use assets and lease liabilities on their balance sheet that arise from leases as well as provide disclosures with respect to certain qualitative and quantitative information related to a company's leasing arrangements to meet the objective of allowing users of financial statements to assess the amount, timing and uncertainty of cash flows arising from leases.

The FASB subsequently issued the following amendments to ASU 2016-02 that have the same effective date and transition date: ASU No. 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842, ASU No. 2018-10, Codification Improvements to Topic 842, Leases, ASU No. 2018-11, Leases (Topic 842): Targeted Improvements, ASU No. 2018-20, Narrow-Scope Improvement for Lessors, and ASU No. 2019-01, Leases (Topic 842): Codification Improvements. We adopted these amendments with ASU 2016-02 (collectively, the new leasing standards) effective January 1, 2019.

We adopted the new leasing standards using the modified retrospective transition approach, as of January 1, 2019, with no restatement of prior periods or cumulative adjustment to retained earnings. Upon adoption, we elected the package of transition practical expedients, which allowed us to carry forward prior conclusions related to whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases and initial direct costs for existing leases. We also elected the practical expedient to not reassess certain land

easements and made an accounting policy election to not recognize leases with an initial term of 12 months or less within our consolidated balance sheets and to recognize those lease payments on a straight-line basis in our consolidated statements of income over the lease term. Upon adoption of the new leasing standards we recognized an operating lease asset of approximately $463.0 million and a corresponding operating lease liability of approximately $526.0 million, which are included in our consolidated balance sheets. The adoption of the new leasing standards did not have an impact on our consolidated statements of income.

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 we will exercise that option.

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 expenses 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 expenses 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 the adoption of the new leasing standards, please read Note 11, 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 revenues can be reasonably estimated. The straight-line method is used when revenues cannot be reasonably estimated. Amortization is recorded within amortization and impairment of acquired intangible assets in our consolidated statements of income.

Acquired and in-licensed rights and patents primarily relate to our acquisition of all remaining rights to TYSABRI from Elan Pharma International Ltd. (Elan), an affiliate of Elan Corporation, plc. Acquired and in-licensed rights and patents also include our rest of world license to Forward Pharma A/S' (Forward Pharma) intellectual property, including Forward Pharma's intellectual property related to TECFIDERA, and other amounts related to our other marketed products and other programs acquired through business combinations. Developed technology primarily relates to our AVONEX product, which was recorded in connection with the merger of Biogen, Inc. and IDEC Pharmaceuticals Corporation in 2003. We amortize the intangible assets related to our TYSABRI, AVONEX, SPINRAZA, VUMERITY and TECFIDERA (rest of world) products using the economic consumption method based on revenues generated from the products underlying the related intangible assets. An analysis of the anticipated

lifetime revenues of our TYSABRI, AVONEX, SPINRAZA, VUMERITY and TECFIDERA (rest of world) products is performed annually during our long-range planning cycle and whenever events or changes in circumstances would significantly affect the anticipated lifetime revenues of our TYSABRI, AVONEX, SPINRAZA, VUMERITY and TECFIDERA (rest of world) 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 revenues from the projects and discounting the net cash flows to present value. The revenues and costs 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 flows to their 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 flows, 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 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. Assets that have been previously impaired, including our vixotrigine (BIIB074) program for the potential treatment of neuropathic pain, such as trigeminal neuralgia (TGN), could become further impaired in the future.

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. Goodwill 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 24, Segment Information, to these consolidated financial statements, we operate in 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 flows resulting from the use of the asset and its eventual disposition. In the event that such cash flows are 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 flows and reserves associated with products upon commercialization, changes in the assumed achievement or timing of any cumulative sales-based and development milestones, changes in the probability of certain clinical events and changes in the assumed probability associated with regulatory approval.

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

Derivative Instruments and Hedging Activities

Cash Flow and Fair Value Derivative Instruments

We recognize all derivative instruments as either assets or liabilities at fair value in our consolidated balance sheets. Changes in the fair value of our derivative instruments are recognized each period in current earnings or 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 flows from these instruments in the same category as the cash flows 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 flows 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

We are exposed to the impact of foreign exchange fluctuations on our investment in the equity of Samsung Bioepis, which is denominated in a currency other than the U.S. dollar, and could adversely impact the U.S. dollar value of this investment. Using derivative instruments, we have hedged our net investment position to mitigate the effects of foreign exchange fluctuations. We recognize these designated net investment hedges 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 flows from these instruments in the same category as the cash flows from the hedged items.

For additional information on our derivative instruments and hedging activities, please read Note 9, 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, 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 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 Expenses

Research and development expenses consist of expenses incurred in performing research and development activities, which include compensation and benefits, facilities and overhead expenses, clinical trial expenses and fees paid to contract research organizations (CROs), clinical supply and manufacturing expenses, write-offs of inventory that was previously capitalized in anticipation of product launch and determined to no longer be realizable and other outside expenses and upfront fees and milestones paid to third-party collaborators. Research and development expenses are 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 18, Collaborative and Other Relationships, to these consolidated financial statements. Because an initial indication has been approved for both RITUXAN and GAZYVA, expenses incurred by Genentech in the ongoing development of RITUXAN and GAZYVA are not recorded as research and development expense, but rather reduce our share of profits recorded as a component of revenues from anti-CD20 therapeutic programs.

For collaborations with commercialized products, if we are the principal, we record revenues 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 Expenses

Selling, general and administrative expenses are 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 expenses and other general and administrative costs.

Advertising costs are expensed as incurred. For the years ended December 31, 2019, 2018 and 2017, advertising costs totaled $79.2 million, $90.2 million and $75.2 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.

In October 2016 the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfer of Assets Other Than Inventory. This standard eliminates the deferral of the tax effects of intra-entity asset transfers other than inventory. As a result, the income tax consequences from the intra-entity transfer of an asset other than inventory and associated changes to deferred taxes will be recognized when the transfer occurs.

We adopted this standard on January 1, 2018, using the modified retrospective method, through a cumulative-effect adjustment to retained earnings as of that date. Upon adoption, we recognized additional net deferred tax assets of approximately $0.5 billion, offset by a corresponding net increase to retained earnings of approximately $0.5 billion. In the fourth quarter of 2018, when we elected to begin recognizing deferred taxes on the GILTI tax calculation, we recorded an additional deferred tax liability of $0.4 billion with a corresponding reduction to

our retained earnings as these differences are related to intra-entity transactions. We will recognize incremental deferred income tax expense thereafter as these deferred tax assets and liabilities are utilized.

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 expense.

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.

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.

Leases

In February 2016 the FASB issued the new leasing standards to increase transparency and comparability among organizations related to their leasing activities. For additional information on the adoption of the new leasing standards, please read the section titled Lease above, and Note 11, Leases, to these consolidated financial statements.

Credit Losses

In June 2016 the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The FASB subsequently issued amendments to ASU 2016-13, which have the same effective date and transition date of January 1, 2020. These standards require that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, these standards now require allowances to be recorded instead of reducing the amortized cost of the investment. These standards limit the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and requires the reversal of previously recognized credit losses if fair value increases.

Based on the composition of our investment portfolio, accounts receivable and other financial assets, current market conditions and historical credit loss activity, the adoption of these standards are not expected to have a material impact on our consolidated financial position and results of operations and related disclosures.

Debt Securities

In March 2017 the FASB issued ASU No. 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities. This standard amends the amortization period for certain purchased callable debt securities held at a premium by shortening the amortization period to the earliest call date. This standard became effective for us on January 1, 2019, and was adopted using a modified retrospective transition approach. The adoption of this standard did not result in a significant adjustment to our marketable debt securities.

Fair Value Measurements

In August 2018 the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. This standard modifies certain disclosure requirements on fair value measurements. This standard became effective for us on January 1, 2020. The adoption of this standard will not have a material impact on our disclosures.

Derivative Instruments and Hedging Activities

In October 2018 the FASB issued ASU No. 2018-16, Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes. This standard permits use of the OIS rate based on the SOFR as a U.S. benchmark interest rate for hedge accounting purposes under ASC 815, Derivatives and Hedging. This standard became effective for us on January 1, 2019, and did not have an impact on our consolidated results of operations or financial position.

Collaborative Arrangements

In November 2018 the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606. This standard makes targeted improvements for collaborative arrangements as follows:

•

Clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606, Revenue from Contracts with Customers, when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement, presentation and disclosure requirements;


•	Adds unit-of-account guidance to ASC 808, Collaborative Arrangements, to align with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606; and


•	Precludes a company from presenting transactions with collaborative arrangement participants that are not directly related to sales to third parties with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer.

This standard became effective for us on January 1, 2020. A retrospective transition approach is required for either all contracts or only for contracts that are not completed at the date of initial application of ASC 606, with a cumulative adjustment to opening retained earnings, as of January 1, 2018. The adoption of this standard did not have a material impact on our consolidated financial position, results of operations and related disclosures.

Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Components of inventories
Raw materials	$ 169.7	$ 196.3
Work in process	460.0	606.7
Finished goods	174.5	133.5
Total inventory	804.2	936.5
Inventory, current	804.2	929.9
Inventory, noncurrent	$ 0.0	$ 6.6

Financial Instruments (Details 3) - USD ($) $ in Millions	12 Months Ended
Financial Instruments (Details 3) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Proceeds from Marketable Debt Securities
Proceeds from maturities and sales	$ 6,007.0	$ 9,173.7	$ 5,565.9
Realized gains	6.0	3.2	3.0
Realized losses	$ (1.5)	$ (11.7)	$ (22.4)

Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Basic and diluted earnings per share

Basic and diluted earnings per share are calculated as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Numerator:
Net income attributable to Biogen Inc.	$	5,888.5	$	4,430.7	$	2,539.1
Denominator:
Weighted average number of common shares outstanding	187.1		204.9		212.6
Effect of dilutive securities:
Stock options and employee stock purchase plan	—		—		0.1
Time-vested restricted stock units	0.2		0.3		0.2
Market stock units	0.1		0.1		0.1
Performance stock units settled in stock	—		—		—
Dilutive potential common shares	0.3		0.4		0.4
Shares used in calculating diluted earnings per share	187.4		205.3		213.0

Financial Instruments

12 Months Ended

Dec. 31, 2019

Investments, All Other Investments [Abstract]

Financial Instruments

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



	As of December 31,
(In millions)	2019		2018
Commercial paper	$	384.4	$	231.2
Overnight reverse repurchase agreements	368.8		—
Money market funds	1,628.5		279.5
Short-term debt securities	159.4		194.8
Total	$	2,541.1	$	705.5

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

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, 2019 (In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities
Current	$	1,057.2	$	1.0	$	—		$	1,058.2
Non-current	633.9		3.0		—			636.9
Government securities
Current	502.9		0.4		—			503.3
Non-current	510.1		0.8		(0.3		)	510.6
Mortgage and other asset backed securities
Current	0.7		—		—			0.7
Non-current	260.2		0.8		(0.4		)	260.6
Total marketable debt securities	$	2,965.0	$	6.0	$	(0.7	)	$	2,970.3
Marketable equity securities, non-current	$	218.4	$	132.1	$	(13.0	)	$	337.5



As of December 31, 2018 (In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities
Current	$	1,608.4	$	—	$	(0.9	)	$	1,607.5
Non-current	854.9		0.7		(3.9		)	851.7
Government securities
Current	706.1		0.1		(0.4		)	705.8
Non-current	264.0		0.1		(0.3		)	263.8
Mortgage and other asset backed securities
Current	0.1		—		—			0.1
Non-current	260.5		0.4		(0.5		)	260.4
Total marketable debt securities	$	3,694.0	$	1.3	$	(6.0	)	$	3,689.3
Marketable equity securities, non-current	$	496.2	$	127.7	$	(8.5	)	$	615.4

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

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



	As of December 31, 2019				As of December 31, 2018
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	1,562.2	$	1,560.8	$	2,313.4	$	2,314.6
Due after one year through five years	1,234.5		1,230.4		1,232.7		1,235.9
Due after five years	173.6		173.8		143.2		143.5
Total marketable debt securities	$	2,970.3	$	2,965.0	$	3,689.3	$	3,694.0

The average maturity of our marketable debt securities available-for-sale as of December 31, 2019 and 2018, were 14 months and 12 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)	2019		2018		2017
Proceeds from maturities and sales	$	6,007.0	$	9,173.7	$	5,565.9
Realized gains	$	6.0	$	3.2	$	3.0
Realized losses	$	1.5	$	11.7	$	22.4

Realized losses for the year ended December 31, 2019, primarily relate to sales of corporate bonds, agency mortgage-backed securities and other asset-backed securities. Realized losses for the year ended December 31, 2018, primarily relate to sales of corporate bonds, agency mortgage-backed securities and other asset-backed securities. Realized losses for the year ended December 31, 2017, primarily relate to impairments recognized on certain of our available-for-sale marketable debt securities, sales of agency mortgage-backed securities, corporate bonds and government securities.

Strategic Investments

As of December 31, 2019 and 2018, our strategic investment portfolio was comprised of investments totaling $393.9 million and $676.3 million, respectively, which are included in 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 7, 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.

Our investments in equity securities include shares of Ionis common stock acquired in June 2018. This investment is classified as a Level 2 marketable security due to certain holding period restrictions and is remeasured each reporting period and carried at fair value. The effect of the holding period restrictions on our investment in Ionis common stock valuation are estimated using an option pricing valuation model. The most significant assumptions within the model are the term of the restrictions and the stock price volatility, which is based upon historical volatility of similar companies. We also use a constant maturity risk-free interest rate to match the remaining term of the restrictions on our investment in Ionis common stock and a dividend yield of zero based upon the fact that Ionis and similar companies generally have not historically granted cash dividends. The remainder of our investments in equity securities of certain publicly-traded biotechnology companies are regularly measured and carried at fair value and classified as Level 1.

The decrease in our strategic investment portfolio for the year ended December 31, 2019, primarily reflects our sale of a portion of our investment in Ionis common stock for approximately $382.0 million as well as our sale of our investment in a non-marketable equity security, partially offset by an increase in the fair value of our remaining investment in Ionis common stock.

For additional information on the June 2018 investment in Ionis common stock, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Samsung Bioepis

In June 2018 we exercised our option under our joint venture agreement with Samsung BioLogics to increase our ownership percentage in Samsung Bioepis from approximately 5% to approximately 49.9%. The share purchase transaction was completed in November 2018 and, upon closing, we paid 759.5 billion South Korean won ($676.6 million) to Samsung BioLogics.

As of December 31, 2019 and 2018, the carrying value of our investment in Samsung Bioepis totaled 670.8 billion South Korean won ($580.2 million) and 759.5 billion South Korean won ($680.6 million), respectively, which is classified as a component of investments and other assets within our consolidated balance sheets.

For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Revenues Other Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Revenues Other Revenues (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total Revenues	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
Royalty
Disaggregation of Revenue [Line Items]
Total Revenues									17.0	38.7	69.8
Other corporate revenues
Disaggregation of Revenue [Line Items]
Total Revenues									584.5	459.4	253.7
Other revenue
Disaggregation of Revenue [Line Items]
Total Revenues	$ 145.7	$ 109.6	$ 160.0	$ 292.4	$ 165.7	$ 147.2	$ 108.6	$ 164.4	707.7	585.9	360.0
Collaborative Arrangement \| AbbVie
Disaggregation of Revenue [Line Items]
Total Revenues									0.0	(8.6)	(16.9)
Collaborative Arrangement \| Samsung Bioepis
Disaggregation of Revenue [Line Items]
Total Revenues									106.2	96.4	42.7
Collaborative Arrangement \| Sobi
Disaggregation of Revenue [Line Items]
Total Revenues									$ 0.0	$ 0.0	$ 10.7

Derivative Instruments (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Gain/Loss on fair value of foreign currency forward contracts	$ (0.5)	$ 27.3	$ (113.0)
Range of durations of foreign currency forward contracts	15 months
Net gains (losses) of other income (expense) related to foreign currency forward contracts	$ 5.9	2.0	$ 4.5
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,892.4	2,239.1
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 793.8	$ 735.1
Interest rate swap \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount				$ 675.0
2.90% Senior Notes due 2020
Derivatives, Fair Value [Line Items]
Interest rate on senior notes	2.90%			2.90%
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	15 months	12 months
Short-term derivative
Derivatives, Fair Value [Line Items]
Gain/Loss on fair value of foreign currency forward contracts	$ 2.4
Range of durations of foreign currency forward contracts	12 months

Commitments and Contingencies (Details Textual) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 02, 2013
Business Acquisition [Line Items]
Maximum contingent consideration in the form of development and approval milestones		$ 735.0
Increase to goodwill		117.5	$ 1,080.1
Potential future milestone payments commitment, approximately		6,800.0
Cancellable future commitments		514.0
Income Taxes Paid		87.0
Commitments And Contingencies (Textual)
Accrued expenses		24.0
Liabilities associated with uncertain tax positions		136.9
TYSABRI
Business Acquisition [Line Items]
Future contingent payment for annual worldwide net sales up to $2.0 billion					18.00%
Future contingent payment threshold					$ 2,000.0
Future contingent payment for annual worldwide net sales that exceed $2.0 billion					25.00%
Solothurn
Business Acquisition [Line Items]
Cancellable future commitments		52.0
TECFIDERA \| Fumapharm AG
Business Acquisition [Line Items]
Increase to goodwill	$ 300.0		1,200.0
Twenty billion \| TECFIDERA \| Fumapharm AG
Business Acquisition [Line Items]
Cumulative sales level	20,000.0		20,000.0
Increase to goodwill	300.0
Each additional one billion up to twenty billion \| TECFIDERA \| Fumapharm AG
Business Acquisition [Line Items]
Cumulative sales level	$ 20,000.0		$ 20,000.0
Development Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		1,200.0
Regulatory Milestones
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		1,400.0
Commercial Milestones [Member]
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		4,200.0
2017 Tax Act
Business Acquisition [Line Items]
Transition toll tax liabilities		$ 697.0		$ 989.6
Ionis Pharmaceuticals \| Minimum \| SPINRAZA
Business Acquisition [Line Items]
Percentage Of Royalties As Per Collaboration		11.00%
Ionis Pharmaceuticals \| Maximum \| SPINRAZA
Business Acquisition [Line Items]
Percentage Of Royalties As Per Collaboration		15.00%
Alkermes
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		$ 155.0
Alkermes \| VUMERITY
Business Acquisition [Line Items]
Percentage Of Royalties As Per Collaboration		15.00%
Twelve months
Business Acquisition [Line Items]
Potential future milestone payments commitment, approximately		$ 430.0

Indebtedness (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Current portion:
Current portion of notes payable	$ 1,495.8	$ 0.0
Non-current portion:
Non-current notes payable	6,000.0
Non-current portion of notes payable	4,459.0	5,936.5
Note payable to Fumedica
Current portion:
2.900% Senior Notes due September 15, 2020	1,495.8	0.0
2.90% Senior Notes due 2020
Non-current portion:
Non-current notes payable	0.0	1,480.8
3.625% Senior Notes due 2022
Non-current portion:
Non-current notes payable	996.6	995.5
4.05% Senior Notes due 2025
Non-current portion:
Non-current notes payable	1,739.5	1,737.8
5.20% Senior Notes due 2045
Non-current portion:
Non-current notes payable	$ 1,722.9	$ 1,722.4

Derivative Instruments Cash Flow Hedges (Details) - Foreign Exchange Contract - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows, revenue \| Revenue
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in operating income for the settlement of certain effective cash flow hedge instruments	$ 118.6	$ (42.5)	$ (32.5)
Net gains (losses) in net income of foreign currency forward contracts, excluded component	2.9	10.8
Cash flows, revenue \| Other income (expense)
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in net income of foreign currency forward contracts, excluded component			8.9
Cash flows, operating expenses \| Other income (expense)
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in net income of foreign currency forward contracts, excluded component			(0.2)
Cash flows, operating expenses \| Operating Expense
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in operating income for the settlement of certain effective cash flow hedge instruments	(3.3)	0.2	$ 0.6
Net gains (losses) in net income of foreign currency forward contracts, excluded component	$ 0.2	$ (0.1)

Employee Benefit Plans Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Domestic Plan
Defined Contribution Plan Disclosure [Line Items]
Minimum Qualifying Age For Employee Benefit Plan	21 years
Expenses related to savings plan	$ 44.8	$ 42.2	$ 42.6
Deferred Compensation Plan
Defined Contribution Plan Disclosure [Line Items]
Deferred compensation liability	$ 114.6	$ 109.3

Income Taxes (Details 2)	12 Months Ended
Income Taxes (Details 2)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Statutory rate	21.00%	21.00%	35.00%
State taxes	0.80%	0.60%	0.80%
Taxes on foreign earnings	(4.50%)	(1.90%)	(11.10%)
Credits and net operating loss utilization	(1.10%)	(0.90%)	(0.80%)
Purchased intangible assets	0.40%	1.20%	1.40%
Effective Income Tax Rate Reconciliation, Disposition of Asset, Percent	1.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Intellectual Property Rights Reorganization	(2.10%)	0.00%	0.00%
Manufacturing deduction	0.00%	0.00%	(1.90%)
2017 Tax Act	0.00%	2.10%	22.90%
Effective Income Tax Rate Reconciliation, Change in Foreign Tax Rate, Percent	(0.80%)	0.00%	0.00%
GILTI	1.50%	1.60%	0.00%
Impairment of ZINBRYTA related tax assets	0.00%	0.00%	0.90%
Permanent items	0.20%	0.30%	0.70%
Other	(0.10%)	0.20%	0.00%
Effective tax rate	16.30%	24.20%	47.90%

Collaborative and Other Relationships - Genentech (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Mar. 31, 2016
Revenues from unconsolidated joint business
Total revenues from anti-cd20 therapeutic programs	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
Genentech
Revenues from unconsolidated joint business
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses									1,542.4	1,431.9	1,316.4
Other revenues from anti-CD20 therapeutic programs									$ 748.0	$ 548.3	$ 242.8
GAZYVA
After First GA101 Threshold Date
Until First GAZYVA Threshold Date	39.00%								39.00%
After First Threshold Date and until Second Threshold Date	37.50%								37.50%
After Second Threshold Date	35.00%								35.00%
RITUXAN
Co-promotion profit sharing formula
Until GAZYVA First Non-CLL FDA Approval	40.00%								40.00%
After First GA101 Threshold Date
Until First GAZYVA Threshold Date	39.00%								39.00%		37.50%		39.00%
After First Threshold Date and until Second Threshold Date	37.50%				37.50%				37.50%	37.50%		37.50%
After Second Threshold Date	35.00%								35.00%
Revenues from anti-cd20 therapeutic programs
Revenues from unconsolidated joint business
Total revenues from anti-cd20 therapeutic programs	$ 600.8	$ 595.8	$ 576.4	$ 517.4	$ 534.9	$ 511.7	$ 490.4	$ 443.2	$ 2,290.4	$ 1,980.2	$ 1,559.2

Subsequent Events Subsequent Events (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Jan. 28, 2020	Jan. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Subsequent Event [Line Items]
Acquired in-process research and development			$ 0.0	$ 112.5	$ 120.0
Senior unsecured revolving credit facility maximum borrowing capacity						$ 1,000.0
Term of credit facility						five
Subsequent Event
Subsequent Event [Line Items]
Acquired in-process research and development		$ 75.0
Estimated additional payments upon achievement of development and commercial milestones		$ 635.0
Senior unsecured revolving credit facility maximum borrowing capacity	$ 1,000.0
Term of credit facility	five

Collaborative and Other Relationships (Tables)

12 Months Ended

Dec. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Co-promotion profit sharing formula

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



Until GAZYVA First Non-CLL FDA Approval	40.0	%
After GAZYVA First Non-CLL FDA Approval until First GAZYVA Threshold Date	39.0	%
After First GAZYVA Threshold Date until Second GAZYVA Threshold Date	37.5	%
After Second GAZYVA Threshold Date	35.0	%

First Non-CLL GAZYVA FDA Approval means the FDA’s first approval of GAZYVA in an indication other than CLL.

First GAZYVA Threshold Date means the earlier of (i) the date of the First Non-CLL GAZYVA FDA approval if U.S. gross sales of GAZYVA for the preceding consecutive 12-month period were at least $150.0 million or (ii) the first day of the calendar quarter after the date of the First Non-CLL GAZYVA FDA Approval that U.S. gross sales of GAZYVA within any consecutive 12-month period have reached $150.0 million.

Second GAZYVA Threshold Date means the first day of the calendar quarter after 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.

Pretax profit sharing formula

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



Until First GAZYVA Threshold Date	39.0	%
After First GAZYVA Threshold Date until Second GAZYVA Threshold Date	37.5	%
After Second GAZYVA Threshold Date	35.0	%

Revenues from anti-CD20 therapeutic programs

Revenues from anti-CD20 therapeutic programs are 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)	2019		2018		2017
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses	$	1,542.4	$	1,431.9	$	1,316.4
Other revenues from anti-CD20 therapeutic programs	748.0		548.3		242.8
Total revenues from anti-CD20 therapeutic programs	$	2,290.4	$	1,980.2	$	1,559.2

Revenues from anti-CD20 therapeutic programs are summarized as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses	$	1,542.4	$	1,431.9	$	1,316.4
Other revenues from anti-CD20 therapeutic programs	748.0		548.3		242.8
Total revenues from anti-CD20 therapeutic programs	$	2,290.4	$	1,980.2	$	1,559.2

Summary of activity related to BAN2401 and Elenbecestat collaboration

A summary of development and sales and marketing expenses related to the BAN2401 and Elenbecestat Collaboration is as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Total development expense incurred by the collaboration related to the advancement of BAN2401 and Elenbecestat	$	348.7	$	232.0	$	146.2
Biogen's share of BAN2401 and Elenbecestat development expense reflected in research and development expense in our consolidated statements of income	$	174.3	$	116.0	$	74.3

Total sales and marketing expense incurred by the collaboration	$	32.4	$	10.7	$	—
Biogen's share of BAN2401 and Elenbecestat sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	$	16.2	$	5.4	$	—

Summary of activity related to Aducanumab collaboration

A summary of development and sales and marketing expenses related to the Aducanumab Collaboration Agreement is as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Total aducanumab development expense	$	179.4	$	264.8	$	268.7
Biogen's share of aducanumab development expense reflected in research and development expense in our consolidated statements of income	$	98.7	$	234.6	$	268.7

Total aducanumab sales and marketing expense incurred by the collaboration	$	27.4	$	50.6	$	23.6
Biogen's share of aducanumab sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	$	15.1	$	27.3	$	23.6

Intangible Assets and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 07, 2019
Intangible assets
Cost	$ 7,379.3				$ 7,187.3					$ 7,379.3	$ 7,187.3
Total intangible assets, gross	8,408.8				7,727.3					8,408.8	7,727.3
Accumulated Amortization	(4,881.4)				(4,607.3)					(4,881.4)	(4,607.3)
Net	2,497.9				2,580.0					2,497.9	2,580.0
Intangible assets, net	3,527.4				3,120.0					3,527.4	3,120.0
Amortization and impairment of acquired intangible assets										489.9	747.3	$ 814.7
Amortization of acquired intangible assets										274.0	381.2	455.3
Contingent Consideration	(2.6)	$ 57.8	$ 20.0	$ (11.5)	(79.3)	$ 87.9	$ (1.9)	$ 5.6		63.7	12.3	$ (62.7)
Intangible Assets and Goodwill (Additional Textual)
Expected future amortization expense, 2020	260.0									260.0
Expected future amortization expense, 2021	220.0									220.0
Expected future amortization expense, 2022	225.0									225.0
Expected future amortization expense, 2023	230.0									230.0
Expected future amortization expense, 2024	220.0									220.0
Increase to goodwill										$ 117.5	1,080.1
Payment made to Forward Pharma									$ 1,250.0
Minimum
Intangible assets
Estimated life, (In Years)										4 years
Maximum
Intangible assets
Estimated life, (In Years)										28 years
In-process research and development
Intangible assets
Indefinite lived intangible assets useful life										Indefinite
Cost and net	965.5				476.0					$ 965.5	476.0
Accumulated Amortization	0.0				0.0					$ 0.0	0.0
Impairment of IPR&D		215.9				189.3
Trademarks and trade names
Intangible assets
Indefinite lived intangible assets useful life										Indefinite
Cost and net	64.0				64.0					$ 64.0	64.0
Accumulated Amortization	0.0				0.0					0.0	$ 0.0
TYSABRI
Intangible assets
Net	1,800.0									1,800.0
VUMERITY
Intangible assets
Net change in acquired and in-licensed rights and patents	155.0
TECFIDERA
Intangible assets
Net	$ 36.1								795.2	$ 36.1
Impairment of in-licensed patent					$ 176.8				$ 328.2
BG00011
Intangible assets
Contingent Consideration		$ 61.2
PLSR \| In-process research and development
Intangible assets
Amortization of acquired intangible assets						60.0
TGN \| In-process research and development
Intangible assets
Cost and net						41.8
Amortization of acquired intangible assets						$ 129.3
Nightstar
Intangible assets
In-process research and development													$ 700.0

Other Consolidated Financial Statement Detail

12 Months Ended

Dec. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Other Consolidated Financial Statement Detail

Supplemental Cash Flow Information

Supplemental disclosure of cash flow information for the years ended December 31, 2019, 2018 and 2017, is as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Cash paid during the year for:
Interest	$	244.2	$	243.2	$	281.7
Income taxes	$	1,064.5	$	1,007.1	$	1,066.4

Non-cash Operating, Investing and Financing Activity

In the fourth quarter of 2018 we accrued $300.0 million upon reaching $20.0 billion in total cumulative sales of the Fumapharm Products, which was paid in the first quarter of 2019. In the fourth quarter of 2017 we accrued $600.0 million upon reaching $15.0 billion and $16.0 billion in total cumulative sales of the Fumapharm Products, which was paid in the first quarter of 2018. These amounts, net of tax benefit, were accounted for as increases to goodwill in accordance with the accounting standard applicable to business combinations when we acquired Fumapharm AG.

In connection with the construction of our large-scale biologics manufacturing facility in Solothurn, Switzerland, we accrued charges related to processing equipment and engineering services of approximately $50.0 million and $100.0 million in our consolidated balance sheets as of December 31, 2019 and 2018, respectively. For additional information on the construction of our manufacturing facility in Solothurn, Switzerland, please read Note 10, Property, Plant and Equipment, to these consolidated financial statements.

Other Income (Expense), Net

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



	For the Years Ended December 31,
(In millions)	2019			2018			2017
Interest income	$	120.0		$	112.5		$	78.5
Interest expense	(187.4		)	(200.6		)	(250.8		)
Gain (loss) on investments, net	204.7			119.5			(36.3		)
Foreign exchange gains (losses), net	(7.0		)	(9.9		)	6.3
Other, net	(47.0		)	(10.5		)	(14.7		)
Total other income (expense), net	$	83.3		$	11.0		$	(217.0	)

Gain (loss) 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.

The following table summarizes our gain (loss) on investments, net that relates to our equity securities held as of December 31, 2019, 2018 and 2017:



	For the Years Ended December 31,
(In millions)	2019		2018			2017
Net gains (losses) recognized during the period on equity securities	$	200.1	$	127.9		$	(19.8	)
Less: Net gains (losses) recognized during the period on equity securities sold during the period	$	50.0	$	(0.6	)	$	—
Unrealized gains (losses) recognized during the period on equity securities held as of December 31	$	150.1	$	128.5		$	(19.8	)

Accrued Expenses and Other

Accrued expenses and other consists of the following:



	As of December 31,
(In millions)	2019		2018
Revenue-related reserves for discounts and allowances	$	1,001.1	$	874.7
Employee compensation and benefits	309.1		320.9
Collaboration expenses	281.6		261.6
Royalties and licensing fees	220.9		224.7
Current portion of contingent consideration obligations	148.4		444.8
Construction in progress	78.0		125.2
Other	726.7		609.3
Total accrued expenses and other	$	2,765.8	$	2,861.2

Other Long-term Liabilities

Other long-term liabilities were $1,348.9 million and $1,389.4 million as of December 31, 2019 and 2018, respectively, and include accrued income taxes totaling $803.3 million and $791.4 million, respectively.

Leases Leases (Tables)

12 Months Ended

Dec. 31, 2019

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:



(In millions)	Balance sheet location	As of December 31, 2019
Assets:
Operating lease assets	Operating lease assets	$	427.0

Liabilities
Current operating lease liabilities	Accrued expenses and other	$	73.6
Non-current operating lease liabilities	Long-term operating lease liabilities	412.7
Total operating lease liabilities		$	486.3

Operating lease costs

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



		For the year ended December 31,
(In millions)	Income Statement Location	2019
Operating lease cost	Research and development	$	6.7
	Selling, general and administrative	84.6
Variable lease cost	Research and development	1.2
	Selling, general and administrative	23.7
Sublease income	Selling, general and administrative	(25.6		)
	Other (income) expense, net	(3.9		)
Net lease cost		$	86.7

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, 2019
2020	$	87.6
2021	81.5
2022	75.7
2023	72.5
2024	69.0
Thereafter	158.3
Total lease payments	$	544.6
Less: interest	58.3
Present value of operating lease liabilities	$	486.3

Minimum lease payments

Under the prior lease accounting guidance minimum rental commitments under non-cancelable leases, net of income from subleases, for each of the five years and total thereafter as of December 31, 2018, were as follows:



(In millions)	2019			2020			2021			2022			2023			Thereafter			Total
Minimum lease payments	$	87.0		$	80.7		$	75.9		$	71.7		$	71.0		$	215.3		$	601.6
Less: income from subleases⁽¹⁾	(26.8		)	(25.6		)	(23.7		)	(24.0		)	(24.3		)	(58.4		)	(182.8		)
Net minimum lease payments	$	60.2		$	55.1		$	52.2		$	47.7		$	46.7		$	156.9		$	418.8

(1)

Represents sublease income expected to be received for the vacated manufacturing facility in Cambridge, MA, the vacated portion of our Weston, MA facility and other facilities throughout the world.

Operating lease weighted average remaining term and discount rate [Table Text Block]

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



	As of December 31, 2019
Weighted average remaining lease term in years	7.07
Weighted average discount rate	3.2	%

Operating lease supplemental cash flow disclosure [Table Text Block]

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



	For the year ended December 31,
(In millions)	2019
Cash paid for amounts included in the measurement of lease liabilities	$	93.8
Operating lease assets obtained in exchange for lease obligations	$	35.9

Revenues (Details Textual) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Revenues (Details Textual) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
Revenues In Percentage From Anti-CD20 Therapeutic Programs									16.00%	15.00%	13.00%
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors									30.00%	32.00%	34.00%
Percentage receivables of wholesale distributor accounted in consolidated receivables	24.10%				27.70%				24.10%	27.70%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors									17.00%	18.00%	21.00%
Percentage receivables of wholesale distributor accounted in consolidated receivables	13.90%				15.60%				13.90%	15.60%
Other revenue
Disaggregation of Revenue [Line Items]
Revenues	$ 145.7	$ 109.6	$ 160.0	$ 292.4	$ 165.7	$ 147.2	$ 108.6	$ 164.4	$ 707.7	$ 585.9	$ 360.0
Other revenue \| Bioverativ
Disaggregation of Revenue [Line Items]
Revenues									383.2	206.7	64.8
Other corporate revenues
Disaggregation of Revenue [Line Items]
Revenues									584.5	$ 459.4	$ 253.7
Revenue, Remaining Performance Obligation, Amount	$ 500.0								$ 500.0

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Income Tax Expense

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



	For the Years Ended December 31,
(In millions)	2019			2018			2017
Income before income taxes (benefit):
Domestic	$	4,725.3		$	3,877.0		$	3,540.4
Foreign	2,400.6			2,022.6			1,588.4
Total	$	7,125.9		$	5,899.6		$	5,128.8
Income tax expense (benefit):
Current:
Federal	$	947.4		$	1,131.8		$	2,201.4
State	59.1			45.5			57.0
Foreign	84.4			140.0			108.6
Total	1,090.9			1,317.3			2,367.0
Deferred:
Federal	$	1,143.9		$	(62.0	)	$	241.0
State	(2.3		)	(7.4		)	9.9
Foreign	(1,074.5		)	177.7			(159.2		)
Total	67.1			108.3			91.7
Total income tax expense	$	1,158.0		$	1,425.6		$	2,458.7

2017 Tax Act

The Tax Cuts and Jobs Act of 2017 (2017 Tax Act) resulted in significant changes to the U.S. corporate income tax system. These changes include a federal statutory rate reduction from 35% to 21%, the elimination or reduction of certain domestic deductions and credits and limitations on the deductibility of interest expense and executive compensation. The 2017 Tax Act also transitions international taxation from a worldwide system to a modified territorial system, which has the effect of subjecting certain earnings of our foreign subsidiaries and collaborations to immediate U.S. taxation as GILTI or Subpart F income, and includes base erosion prevention measures on U.S. earnings and the reduced effective tax rate on income that comes from U.S. exports, called Foreign Derived Intangible Income. These changes became effective in 2018.

During the fourth quarter of 2017 we recognized within our provision for income taxes a $1.2 billion estimate pursuant to the U.S. Securities and Exchange Commission Staff Accounting Bulletin No. 118. Our estimate included an amount of $989.6 million associated with a one-time mandatory deemed repatriation tax on accumulated foreign subsidiaries' previously untaxed foreign earnings (the Transition Toll Tax), as discussed below, and $184.0 million related to the impact of remeasuring our deferred tax balances to reflect the new federal statutory rate and other changes to U.S. tax law.

During the year ended December 31, 2018, we recognized a net reduction of $34.6 million in our estimated Transition Toll Tax, an expense of $12.7 million to remeasure our deferred tax balances, an expense of $135.8 million related to establishing deferred taxes for GILTI and an expense of $11.0 million to reflect other aspects of the 2017 Tax Act.

Transition Toll Tax

The 2017 Tax Act eliminated the deferral of U.S. income tax on the historical unrepatriated earnings by imposing 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, 2019 and 2018, we have accrued income tax liabilities of $697.0 million under the Transition Toll Tax. Of the amounts accrued as of December 31, 2019, no amounts are expected to be paid within one year due to an approximately $87.0 million carryforward of taxes paid in relation to the company's 2017 tax return. The Transition Toll Tax will be paid over an eight--year period, which started in 2018, and does not accrue interest.

Unremitted Earnings

At December 31, 2019, 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, 2019, 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, 2019. The residual U.S. tax liability, if these differences reverse, would be between $0.3 billion and $0.4 billion as of December 31, 2019.

Article 20 Procedure of ZINBRYTA

In 2017 the European Medicines Agency initiated a review (referred to as an Article 20 Procedure) of ZINBRYTA following the report of a case of fatal fulminant liver failure, as well as four cases of serious liver injury. As a result of the Article 20 Procedure of ZINBRYTA, for the year ended December 31, 2017, we recognized a net impairment charge on certain tax assets related to ZINBRYTA reflected within income tax expense of $48.8 million. This charge reflected the write-off of $142.6 million related to prepaid taxes, which was partially offset by the recognition of an unrecorded deferred tax benefit of $93.8 million. For additional information on our collaboration arrangement with AbbVie, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Deferred Tax Assets and Liabilities

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



	As of December 31,
(In millions)	2019			2018
Deferred tax assets:
Tax credits	$	106.6		$	102.8
Inventory, other reserves and accruals	162.0			163.9
Intangibles, net	3,380.0			2,298.6
Net operating loss	130.4			213.1
Share-based compensation	23.8			25.8
Other	103.7			38.9
Valuation allowance	(1.1		)	(20.0		)
Total deferred tax assets	$	3,905.4		$	2,823.1
Deferred tax liabilities:
Purchased intangible assets	$	(350.3	)	$	(232.8	)
GILTI	(1,381.6		)	(544.6		)
Tax credits	(1,617.2		)	(1,425.7		)
Depreciation, amortization and other	(135.0		)	(102.3		)
Total deferred tax liabilities	$	(3,484.1	)	$	(2,305.4	)

In addition to deferred tax assets and liabilities, we have recorded prepaid tax and deferred charges related to intra-entity sales of inventory. As of December 31, 2019 and 2018, the total deferred charges and prepaid taxes were $243.8 million and $239.2 million, respectively.

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,
	2019		2018		2017
Statutory rate	21.0	%	21.0	%	35.0	%
State taxes	0.8		0.6		0.8
Taxes on foreign earnings	(4.5	)	(1.9	)	(11.1	)
Credits and net operating loss utilization	(1.1	)	(0.9	)	(0.8	)
Purchased intangible assets	0.4		1.2		1.4
Divestiture of Denmark manufacturing operations	1.0		—		—
Internal reorganization of certain intellectual property rights	(2.1	)	—		—
GILTI	1.5		1.6		—
Other permanent items	0.2		0.3		0.7
U.S. tax reform	—		2.1		22.9
Swiss tax reform	(0.8	)	—		—
Manufacturing deduction	—		—		(1.9	)
Impairment of ZINBRYTA related tax assets	—		—		0.9
Other	(0.1	)	0.2		—
Effective tax rate	16.3	%	24.2	%	47.9	%

Changes in Tax Rate

For the year ended December 31, 2019, as compared to 2018, the decrease in our effective tax rate was primarily due to the combination of the internal reorganization of certain intellectual property rights and the impact of the enactment of a new taxing regime in the country and certain cantons of Switzerland. This decrease was partially offset by a $68.9 million tax expense related to the divestiture of our subsidiary that owned our Hillerød, Denmark manufacturing operations. We also had a higher effective tax rate in 2018 resulting from the unfavorable effects of

the 2017 Tax Act and our sale of inventory, the tax effect of which had been included within prepaid taxes at January 1, 2018, at a higher effective tax rate than the 2018 statutory tax rate.

Although we are recognizing a loss on the divestiture of our Hillerød, Denmark manufacturing operations, the divestiture required us to write-off certain deferred tax assets and resulted in a taxable gain in certain jurisdictions.

As a result of the internal reorganization of certain intellectual property rights, we recorded a deferred tax asset of $754.1 million and a deferred tax liability of $603.3 million as of December 31, 2019.

For the year ended December 31, 2018, as compared to 2017, the decrease in our effective tax rate was primarily due to the enactment of the 2017 Tax Act. The effects of an overall reduction in the federal statutory rate in the U.S. were partially offset by the elimination of the manufacturing deduction, the imposition of the GILTI tax on international earnings, our recording of deferred taxes on GILTI in 2018, limits on the deductibility of certain benefits on executive compensation and a reduction in the tax benefit associated with the Orphan Drug Credit, all resulting from the 2017 Tax Act, and a change in accounting rules related to recording the tax impacts of intra-entity transactions.

Tax Attributes

As of December 31, 2019, we had net operating losses and general business credit carry forwards for federal income tax purposes of approximately $0.7 million and $1.3 million, respectively, which begin to expire in 2022. Additionally, for state income tax purposes, we had net operating loss carry forwards of approximately $4.6 million that begin to expire in 2020. For state income tax purposes, we had research and investment credit carry forwards of approximately $133.8 million that begin to expire in 2020. For foreign income tax purposes, we had $1,773.8 million of net operating loss carryforwards that begin to expire in 2025.

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. In the event that actual results differ from our estimates or we adjust our estimates in future periods, we may need to 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:



	For the Years Ended December 31,
(In millions)	2019			2018			2017
Balance at January 1,	$	114.2		$	66.8		$	32.4
Additions based on tax positions related to the current period	5.3			0.5			5.7
Additions for tax positions of prior periods	17.2			58.7			7.3
Reductions for tax positions of prior periods	(10.3		)	(13.6		)	(21.8		)
Statute expirations	(0.1		)	(2.9		)	(1.4		)
Settlement refund (payment)	3.6			4.7			44.6
Balance at December 31,	$	129.9		$	114.2		$	66.8

Our 2017 activity reflects a refund received from a state related to the settlement of an uncertain tax position.

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 2013 or state, local or non-U.S. income tax examinations for years before 2012.

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, 2019, 2018 and 2017, are $122.7 million, $109.1 million and $64.3 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. In 2019, 2018 and 2017 we recognized a net interest expense of $4.7 million, $2.2 million and $4.8 million, respectively. We have accrued $20.0 million and $13.8 million for the payment of interest and penalties as of December 31, 2019 and 2018, respectively.

Accounting for Uncertainty in Income Taxes

On February 1, 2017, in connection with the spin-off of our hemophilia business, we distributed all of the then outstanding shares of Bioverativ common stock to Biogen shareholders pursuant to a separation agreement. In March 2018 Bioverativ was acquired by Sanofi S.A. (Sanofi) and is now an indirect wholly-owned subsidiary of Sanofi. The spin-off of our hemophilia business was intended to qualify for tax-free treatment to Biogen and its shareholders under the Internal Revenue Code. Our 2017 tax return remains open to audit. Bioverativ and Sanofi agreed to indemnify us for certain potential liabilities that may arise.

Federal and State Uncertain Tax Positions

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 $75.0 million in the next 12 months as a result of various audit closures, settlements and expiration of the statute of limitations.

Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2019

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)	2019			2018			2017
Research and development	$	77.1		$	75.8		$	74.0
Selling, general and administrative	148.3			105.8			95.7
Subtotal	225.4			181.6			169.7
Capitalized share-based compensation costs	(8.9		)	(11.5		)	(9.6		)
Share-based compensation expense included in total cost and expenses	216.5			170.1			160.1
Income tax effect	(35.7		)	(27.5		)	(42.8		)
Share-based compensation expense included in net income attributable to Biogen Inc.	$	180.8		$	142.6		$	117.3

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)	2019			2018			2017
Market stock units	$	30.4		$	27.2		$	22.4
Time-vested restricted stock units	134.0			126.6			107.3
Cash settled performance units	0.7			7.8			18.4
Performance units	1.6			3.1			12.3
Performance stock units settled in stock	15.5			4.7			—
Performance stock units settled in cash	5.5			1.7			—
Employee stock purchase plan	11.5			10.5			9.3
NST stock options	26.2			—			—
Subtotal	225.4			181.6			169.7
Capitalized share-based compensation costs	(8.9		)	(11.5		)	(9.6		)
Share-based compensation expense included in total cost and expenses	$	216.5		$	170.1		$	160.1

Stock option activity

The following table summarizes our stock option activity:



	Shares		Weighted Average Exercise Price
Outstanding at December 31, 2018	27,000		$	53.82
Granted	—		$	—
Exercised	(15,000	)	$	50.03
Cancelled	—		$	—
Outstanding at December 31, 2019	12,000		$	58.46

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 stock options:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Tax benefit realized for stock options	$	2.5	$	2.2	$	3.4
Cash received from the exercise of stock options	$	0.4	$	0.8	$	0.7

Market stock units activity

The following table summarizes our MSU activity:



	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	180,000		$	371.32
Granted (a)	147,000		$	378.08
Vested	(101,000	)	$	356.71
Forfeited	(43,000	)	$	388.68
Unvested at December 31, 2019	183,000		$	378.09

Assumptions used in valuation of market based stock units

he assumptions used in our valuation are summarized as follows:



	For the Years Ended December 31,
	2019	2018	2017
Expected dividend yield	—%	—%	—%
Range of expected stock price volatility	31.2% - 33.6%	27.5% - 32.4%	33.0% - 35.6%
Range of risk-free interest rates	2.46% - 2.53%	1.9% - 2.3%	0.9% - 1.6%
30 calendar day average stock price on grant date	$228.59 - $331.18	$279.47 - $346.76	$263.18 - $267.88
Weighted-average per share grant date fair value	$378.08	$378.85	$382.59

Cash settled performance shares activity

The following table summarizes our CSPU activity:



	Shares
Unvested at December 31, 2018	50,000
Granted	—
Vested	(33,000	)
Forfeited	(4,000	)
Unvested at December 31, 2019	13,000

Performance units activity

The following table summarizes our PU activity:



	Shares
Unvested at December 31, 2018	48,000
Granted	—
Vested	(33,000	)
Forfeited	(4,000	)
Unvested at December 31, 2019	11,000

Performance stock units settled in stock activity

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



	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	60,000		$	317.26
Granted (a)	77,000		$	316.28
Vested	—		$	—
Forfeited	(26,000	)	$	318.11
Unvested at December 31, 2019	111,000		$	316.39

Performance stock units settled in cash activity

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



	Shares
Unvested at December 31, 2018	40,000
Granted (a)	63,000
Vested	(1,000	)
Forfeited	(20,000	)
Unvested at December 31, 2019	82,000

Time-vested restricted stock units activity

The following table summarizes our RSU activity:



	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	903,000		$	303.18
Granted (a)	602,000		$	304.44
Vested	(416,000	)	$	294.71
Forfeited	(151,000	)	$	311.07
Unvested at December 31, 2019	938,000		$	306.55

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)	2019		2018		2017
Shares issued under the 2015 ESPP	204,000		170,000		167,000
Cash received under the 2015 ESPP	$	40.4	$	40.5	$	39.8

Segment Information (Tables)

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

Geographic information

The following tables contain certain financial information by geographic area:



December 31, 2019 (In millions)	U.S.		Europe		Asia		Other		Total
Product revenues from external customers	$	6,713.8	$	3,794.5	$	320.3	$	551.2	$	11,379.8
Revenues from anti-CD20 therapeutic programs	$	2,211.9	$	0.2	$	—	$	78.3	$	2,290.4
Other revenues from external customers	$	585.8	$	9.7	$	112.2	$	—	$	707.7
Long-lived assets	$	1,493.2	$	2,162.9	$	6.2	$	12.0	$	3,674.3

December 31, 2018 (In millions)	U.S.		Europe		Asia		Other		Total
Product revenues from external customers	$	6,800.5	$	3,370.3	$	281.2	$	434.8	$	10,886.8
Revenues from anti-CD20 therapeutic programs	$	1,903.4	$	0.2	$	—	$	76.6	$	1,980.2
Other revenues from external customers	$	457.0	$	32.7	$	96.2	$	—	$	585.9
Long-lived assets	$	1,152.7	$	2,442.8	$	3.9	$	1.8	$	3,601.2

December 31, 2017 (In millions)	U.S.		Europe		Asia		Other		Total
Product revenues from external customers	$	7,017.1	$	2,844.8	$	160.1	$	332.7	$	10,354.7
Revenues from anti-CD20 therapeutic programs	$	1,475.6	$	0.6	$	—	$	83.0	$	1,559.2
Other revenues from external customers	$	249.5	$	67.8	$	42.7	$	—	$	360.0
Long-lived assets	$	1,226.9	$	1,948.2	$	5.2	$	2.1	$	3,182.4

Equity Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning Balance	$ (240,400,000)	$ (318,400,000)	$ (319,900,000)
Balance, January 1, 2018	(240,400,000)	(318,400,000)	(319,900,000)	$ (316,900,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	230,800,000	29,500,000	(42,700,000)
Amounts Reclassified From Accumulated Other Comprehensive Income, Net of Tax	(125,600,000)	47,000,000.0	44,200,000
Other comprehensive income (loss), net of tax	105,200,000	76,500,000	1,500,000
Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance	(135,200,000)	(240,400,000)	(318,400,000)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning Balance	(4,000,000.0)	(1,600,000)	(10,800,000)
Balance, January 1, 2018	4,200,000	(1,600,000)	(10,800,000)	(100,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	11,800,000	(10,600,000)	(3,500,000)
Amounts Reclassified From Accumulated Other Comprehensive Income, Net of Tax	(3,600,000)	6,700,000	12,700,000
Other comprehensive income (loss), net of tax	8,200,000	(3,900,000)	9,200,000
Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance	4,200,000	(4,000,000.0)	(1,600,000)
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning Balance	34,700,000	(104,500,000)	57,800,000
Balance, January 1, 2018	7,800,000	(104,500,000)	57,800,000	(104,500,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	88,100,000	97,400,000	(193,800,000)
Amounts Reclassified From Accumulated Other Comprehensive Income, Net of Tax	(115,000,000.0)	41,800,000	31,500,000
Other comprehensive income (loss), net of tax	(26,900,000)	139,200,000	(162,300,000)
Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance	7,800,000	34,700,000	(104,500,000)
Gains (Losses) on Net Investment Hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning Balance	3,500,000	0	0
Balance, January 1, 2018	25,100,000	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	28,600,000	5,000,000.0	0
Amounts Reclassified From Accumulated Other Comprehensive Income, Net of Tax	(7,000,000.0)	(1,500,000)	0
Other comprehensive income (loss), net of tax	21,600,000	3,500,000	0
Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance	25,100,000	3,500,000	0
Unfunded Status of Post Retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning Balance	(31,300,000)	(36,800,000)	(32,700,000)
Balance, January 1, 2018	(32,800,000)	(36,800,000)	(32,700,000)	(36,800,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1,500,000)	5,500,000	(4,100,000)
Amounts Reclassified From Accumulated Other Comprehensive Income, Net of Tax	0	0	0
Other comprehensive income (loss), net of tax	(1,500,000)	5,500,000	(4,100,000)
Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance	(32,800,000)	(31,300,000)	(36,800,000)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning Balance	(243,300,000)	(175,500,000)	(334,200,000)
Balance, January 1, 2018	(139,500,000)	(175,500,000)	(334,200,000)	(175,500,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	103,800,000	(67,800,000)	158,700,000
Amounts Reclassified From Accumulated Other Comprehensive Income, Net of Tax	0	0	0
Other comprehensive income (loss), net of tax	103,800,000	(67,800,000)	158,700,000
Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance	$ (139,500,000)	$ (243,300,000)	$ (175,500,000)
Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption				1,500,000
Accounting Standards Update 2016-01 \| Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption				1,500,000
Accounting Standards Update 2016-01 \| Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption				0
Accounting Standards Update 2016-01 \| Gains (Losses) on Net Investment Hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption				0
Accounting Standards Update 2016-01 \| Unfunded Status of Post Retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption				0
Accounting Standards Update 2016-01 \| Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ 0

Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data (Unaudited)



(In millions, except per share amounts)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Total Year
2019
Product revenues, net	$	2,680.0	$	2,880.3	$	2,894.7	$	2,924.8	$	11,379.8
Revenues from anti-CD20 therapeutic programs	$	517.4	$	576.4	$	595.8	$	600.8	$	2,290.4
Other revenues	$	292.4	$	160.0	$	109.6	$	145.7	$	707.7
Total revenues	$	3,489.8	$	3,616.7	$	3,600.1	$	3,671.3	$	14,377.9
Gross profit ⁽¹⁾	$	2,887.8	$	3,140.4	$	3,170.1	$	3,224.2	$	12,422.5
Net income ^(a)	$	1,408.8	$	1,494.1	$	1,545.9	$	1,439.7	$	5,888.5
Net income attributable to Biogen Inc. ^(a)	$	1,408.8	$	1,494.1	$	1,545.9	$	1,439.7	$	5,888.5
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$	7.17	$	7.85	$	8.40	$	8.10	$	31.47
Diluted earnings per share attributable to Biogen Inc.	$	7.15	$	7.85	$	8.39	$	8.08	$	31.42
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	196.6		190.3		184.0		177.8		187.1
Diluted earnings per share attributable to Biogen Inc.	197.0		190.4		184.2		178.2		187.4



(In millions, except per share amounts)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Total Year
2018
Product revenues, net	$	2,523.5	$	2,757.5	$	2,780.1	$	2,825.7	$	10,886.8
Revenues from anti-CD20 therapeutic programs	$	443.2	$	490.4	$	511.7	$	534.9	$	1,980.2
Other revenues	$	164.4	$	108.6	$	147.2	$	165.7	$	585.9
Total revenues	$	3,131.1	$	3,356.5	$	3,439.0	$	3,526.3	$	13,452.9
Gross profit ⁽¹⁾	$	2,685.1	$	2,935.5	$	2,978.2	$	3,037.8	$	11,636.6
Net income ^(b)	$	1,171.2	$	915.0	$	1,442.9	$	944.9	$	4,474.0
Net income attributable to Biogen Inc. ^(b)	$	1,172.9	$	866.6	$	1,444.4	$	946.8	$	4,430.7
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$	5.55	$	4.18	$	7.17	$	4.74	$	21.63
Diluted earnings per share attributable to Biogen Inc.	$	5.54	$	4.18	$	7.15	$	4.73	$	21.58
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	211.4		207.1		201.4		199.8		204.9
Diluted earnings per share attributable to Biogen Inc.	211.7		207.3		201.9		200.3		205.3

(1) Gross profit is calculated as total revenues less cost of sales, excluding amortization and impairment of acquired intangible assets.


(a)	Net income and net income attributable to Biogen Inc. for 2019 include:


•	Pre-tax gains (losses) related to changes in the fair value of our strategic investments of $376.1 million, ($174.2) million, ($4.6) million and $2.8 million for the first, second, third and fourth quarters, respectively.


•	Impairment charges related to certain intangible assets of $215.9 million in the third quarter. For additional information, please read Note 6, Intangible Assets and Goodwill, to these consolidated financial statements.

•

A total net loss in our consolidated statements of income of approximately $124.2 million related to the sale of all the outstanding shares of our subsidiary that owned our biologics manufacturing operations in Hillerød, Denmark to FUJIFILM. This loss included a pre-tax loss of $55.3 million and a tax expense of $68.9 million related to this transaction. For additional information on the divestiture of our Hillerød, Denmark manufacturing operations, please read, Note 3, Divestitures, to these consolidated financial statements.

•

An expense of $63.0 million was recorded in research and development expense in our consolidated statements of income in the fourth quarter as we completed a transaction with Samsung Bioepis and secured the exclusive rights to commercialize two potential ophthalmology biosimilar products, SB11 referencing LUCENTIS and SB15 referencing EYLEA, in major markets worldwide, including the U.S., Canada, Europe, Japan and Australia. We also acquired an option to extend our existing commercial agreement with Samsung Bioepis for BENEPALI, IMRALDI and FLIXABI in Europe and obtained exclusive rights to commercialize these products in China. For additional information, please read, Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

•

Losses (gains) related to the adjustments to the fair values of our contingent consideration obligations of $11.5 million, $(20.0) million, $(57.8) million and $2.6 million for the first, second, third and fourth quarters, respectively. For additional information on the valuation of our contingent consideration obligations, please read Note 7, Fair Value Measurements, to these consolidated financial statements.


•	A payment of $45.0 million to Ionis in the fourth quarter, as we exercised our option to obtain a worldwide, exclusive, royalty-bearing license from Ionis to develop and commercialize BIIB080. For additional information, please read, Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

•

A payment of $38.5 million to Skyhawk in the first quarter as we entered into a collaboration and research and development services agreement with Skyhawk pursuant to which the companies are leveraging Skyhawk's SkySTAR technology platform with the goal of discovering innovative small molecule treatments for patients with neurological diseases, including MS and SMA. For additional information, please read, Note 18, Collaborative and Other Relationships, to these consolidated financial statements.


(b)	Net income and net income attributable to Biogen Inc. for 2018 include:


•	Pre-tax (losses) gains related to changes in the fair value of our strategic investments of $(6.4) million, $5.4 million, $141.2 million and $(12.2) million for the first, second, third and fourth quarters, respectively.


•	Pre-tax charges to acquired IPR&D of $10.0 million, $75.0 million and $27.5 million for the first, second and third quarters, respectively, for upfront payments made upon closing of asset purchase transactions. For additional information, please read Note 2, Acquisitions, to these consolidated financial statements.


•	Pre-tax research and development expenses for the second quarter of $486.2 million related to the 2018 Ionis Agreement. For additional information, please read, Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

•

Pre-tax charge to noncontrolling interests of $50.0 million for the second quarter for a payment to Neurimmune in exchange for a 5% reduction in the previously negotiated royalty rates payable on products developed under the Neurimmune Agreement, including royalties payable on potential commercial sales of aducanumab. For additional information, please read Note 19, Investments in Variable Interest Entities, to these consolidated financial statements.


•	Impairment charges related to certain intangible assets of $189.3 million and $176.8 million in the third and fourth quarters, respectively. For additional information, please read Note 6, Intangible Assets and Goodwill, to these consolidated financial statements.


•	Losses (gains) related to the adjustments to the fair values of our contingent consideration obligations of $(5.6) million, $1.9 million, $(87.9) million and $79.3 million for the first, second, third and fourth quarters,

respectively. For additional information, please read Note 7, Fair Value Measurements, to these consolidated financial statements.


•	Net increase to income tax expense of $135.8 million for the fourth quarter reflecting the impact of electing to record deferred taxes on GILTI. For additional information, please read Note 16, Income Taxes, to these consolidated financial statements.

•

An upfront payment of $35.0 million to Ionis, as we exercised our option in the fourth quarter to obtain a worldwide, exclusive, royalty-bearing license from Ionis to develop and commercialize tofersen. For additional information, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Equity (Tables)

12 Months Ended

Dec. 31, 2019

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, 2019, 2018 and 2017:

As of December 31, 2019

As of December 31, 2018

As of December 31, 2017

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

198.0

174.2

1,000.0

221.0

197.2

1,000.0

235.3

211.5

Revenues Reserves for Discounts and Allowances (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 1,051.3	$ 761.6	$ 605.5
Current provisions relating to sales in current year	3,698.6	3,389.1	2,917.3
Adjustments relating to prior years	(48.3)	(12.1)	6.0
Payments/returns related to sales in current year	(2,778.6)	(2,440.4)	(2,232.8)
Payments/returns related to sales in prior years	(724.1)	(646.9)	(534.4)
Ending balance	1,198.9	1,051.3	761.6
Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	127.8	109.6	71.6
Current provisions relating to sales in current year	666.2	679.3	583.0
Adjustments relating to prior years	0.3	(0.3)	(0.1)
Payments/returns related to sales in current year	(535.5)	(551.7)	(475.8)
Payments/returns related to sales in prior years	(127.7)	(109.1)	(69.1)
Ending balance	131.1	127.8	109.6
Contractual Adjustments
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	888.8	606.0	482.7
Current provisions relating to sales in current year	3,011.5	2,686.7	2,307.4
Adjustments relating to prior years	(54.1)	(10.0)	15.0
Payments/returns related to sales in current year	(2,242.9)	(1,887.6)	(1,756.9)
Payments/returns related to sales in prior years	(576.0)	(506.3)	(442.2)
Ending balance	1,027.3	888.8	606.0
Returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	34.7	46.0	51.2
Current provisions relating to sales in current year	20.9	23.1	26.9
Adjustments relating to prior years	5.5	(1.8)	(8.9)
Payments/returns related to sales in current year	(0.2)	(1.1)	(0.1)
Payments/returns related to sales in prior years	(20.4)	(31.5)	(23.1)
Ending balance	$ 40.5	$ 34.7	$ 46.0

Fair Value Measurements (Details 1) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument
Notes payable, fair value	$ 6,553.6	$ 6,037.6
2.90% Senior Notes due 2020
Debt Instrument
Notes payable, fair value	1,509.6	1,489.5
3.625% Senior Notes due 2022
Debt Instrument
Notes payable, fair value	1,038.9	1,000.4
4.05% Senior Notes due 2025
Debt Instrument
Notes payable, fair value	1,897.2	1,745.1
5.20% Senior Notes due 2045
Debt Instrument
Notes payable, fair value	$ 2,107.9	$ 1,802.6

Share-Based Payments (Details 5) - Market stock units - USD ($)

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Assumptions used in valuation of market based stock units

Expected dividend yield

0.00%

Minimum range of risk-free interest rates

2.50%

1.90%

0.90%

Maximum range of risk-free interest rates

2.50%

2.30%

1.60%

Average stock price on grant date minimum

$ 228.59

$ 279.47

$ 263.18

Average stock price on grant date maximum

$ 331.18

$ 346.76

$ 267.88

Weighted average grant date fair value

$ 378.08

^[1]

$ 378.85

$ 382.59

Minimum

Assumptions used in valuation of market based stock units

Range of expected stock price volatility

31.20%

27.50%

33.00%

Maximum

Assumptions used in valuation of market based stock units

Range of expected stock price volatility

33.60%

32.40%

35.60%

[1]

MSUs granted during 2019 include awards granted in conjunction with our annual awards made in February 2019 and MSUs 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. MSUs granted in 2019 also reflect an adjustment based upon the final performance multiplier in relation to shares granted in 2018, 2017 and 2016.

Leases Leases

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

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 ten 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 less than one year to nine 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:



(In millions)	Balance sheet location	As of December 31, 2019
Assets:
Operating lease assets	Operating lease assets	$	427.0

Liabilities
Current operating lease liabilities	Accrued expenses and other	$	73.6
Non-current operating lease liabilities	Long-term operating lease liabilities	412.7
Total operating lease liabilities		$	486.3

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



		For the year ended December 31,
(In millions)	Income Statement Location	2019
Operating lease cost	Research and development	$	6.7
	Selling, general and administrative	84.6
Variable lease cost	Research and development	1.2
	Selling, general and administrative	23.7
Sublease income	Selling, general and administrative	(25.6		)
	Other (income) expense, net	(3.9		)
Net lease cost		$	86.7

Variable lease cost primarily related to operating expenses, 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, 2019
2020	$	87.6
2021	81.5
2022	75.7
2023	72.5
2024	69.0
Thereafter	158.3
Total lease payments	$	544.6
Less: interest	58.3
Present value of operating lease liabilities	$	486.3



(In millions)	2019			2020			2021			2022			2023			Thereafter			Total
Minimum lease payments	$	87.0		$	80.7		$	75.9		$	71.7		$	71.0		$	215.3		$	601.6
Less: income from subleases⁽¹⁾	(26.8		)	(25.6		)	(23.7		)	(24.0		)	(24.3		)	(58.4		)	(182.8		)
Net minimum lease payments	$	60.2		$	55.1		$	52.2		$	47.7		$	46.7		$	156.9		$	418.8


(1)	Represents sublease income expected to be received for the vacated manufacturing facility in Cambridge, MA, the vacated portion of our Weston, MA facility and other facilities throughout the world.

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



	As of December 31, 2019
Weighted average remaining lease term in years	7.07
Weighted average discount rate	3.2	%

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



	For the year ended December 31,
(In millions)	2019
Cash paid for amounts included in the measurement of lease liabilities	$	93.8
Operating lease assets obtained in exchange for lease obligations	$	35.9

Derivative Instruments Derivative Instruments Net Investment Hedges (Details 1) $ in Millions, ₩ in Billions	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 KRW (₩)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Feb. 29, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Payments to increase investment in Samsung Bioepis			$ 0.0	$ 676.6	$ 0.0
Unrealized gain (loss) on net investment hedge in AOCI			$ 0.5	(27.3)	$ 113.0
Net Investment Hedge
Derivative Instruments, Gain (Loss) [Line Items]
Forward contracts duration			10 months
Unrealized gain (loss) on net investment hedge in AOCI			$ 1.5	3.8
Derivative qualifying as hedge, excluded component, after tax	$ 7.3		2.9	7.3
Gains (losses) on net investment hedge			25.3	(3.8)
Gains (losses) on net investment hedge, excluded component			3.3	0.0
Other income (expense) \| Net Investment Hedge
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) in net income of foreign currency forward contracts, excluded component			$ 7.0	$ 1.5
Samsung Bioepis
Derivative Instruments, Gain (Loss) [Line Items]
Samsung Bioepis, ownership percentage before additional purchase transaction	5.00%			5.00%
Samsung Bioepis, ownership percentage			49.90%			15.00%
Payments to increase investment in Samsung Bioepis	$ 676.6	₩ 759.5

Income Taxes (Details 3) - USD ($) $ in Millions	12 Months Ended
Income Taxes (Details 3) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of the beginning and ending of unrecognized tax benefits
Balance at January 1	$ 114.2	$ 66.8	$ 32.4
Additions based on tax positions related to the current period	5.3	0.5	5.7
Additions for tax positions of prior periods	17.2	58.7	7.3
Reductions for tax positions of prior periods	(10.3)	(13.6)	(21.8)
Statute expirations	(0.1)	(2.9)	(1.4)
Settlements	3.6	4.7	44.6
Balance at December 31	$ 129.9	$ 114.2	$ 66.8

Share-Based Payments (Details 9) - Performance stock units settled in cash shares in Thousands	12 Months Ended
	Dec. 31, 2019 shares
Performance stock units settled in cash
Beginning Balance, Unvested, Shares	40,000
Shares, Granted	63,000
Shares, Vested	(1,000)
Shares, Forfeited	(20,000)
Ending Balance, Unvested, Shares	82,000

Litigation Litigation (Details)	12 Months Ended
Litigation Litigation (Details)	Dec. 31, 2019 USD ($)
Income Tax Contingency [Line Items]
Loss Contingency, Claims Asserted	$ 200,000,000.0
BRAZIL
Income Tax Contingency [Line Items]
Loss Contingency, Tax Assessment	$ 70,000,000.0

Label	Element	Value
Additional Paid-in Capital [Member]
Share-based Payment Arrangement, Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ (138,100,000)

Equity Accumulated Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Dec. 31, 2019

Accumulated Other Comprehensive Income (Loss) [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

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



(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 Hedge, Net of Tax			Unfunded Status of Postretirement Benefit Plans, net of tax			Currency Translation Adjustments			Total
Balance, December 31, 2018	$	(4.0	)	$	34.7		$	3.5		$	(31.3	)	$	(243.3	)	$	(240.4	)
Other comprehensive income (loss) before reclassifications	11.8			88.1			28.6			(1.5		)	103.8			230.8
Amounts reclassified from accumulated other comprehensive income (loss)	(3.6		)	(115.0		)	(7.0		)	—			—			(125.6		)
Net current period other comprehensive income (loss)	8.2			(26.9		)	21.6			(1.5		)	103.8			105.2
Balance, December 31, 2019	$	4.2		$	7.8		$	25.1		$	(32.8	)	$	(139.5	)	$	(135.2	)



(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 Hedge, Net of Tax			Unfunded Status of Postretirement Benefit Plans, net of tax			Currency Translation Adjustments			Total
Balance, December 31, 2017	$	(1.6	)	$	(104.5	)	$	—		$	(36.8	)	$	(175.5	)	$	(318.4	)
Amounts reclassified, net of tax, upon adoption of ASU 2016-01	1.5			—			—			—			—			1.5
Balance, January 1, 2018	(0.1		)	(104.5		)	—			(36.8		)	(175.5		)	(316.9		)
Other comprehensive income (loss) before reclassifications	(10.6		)	97.4			5.0			5.5			(67.8		)	29.5
Amounts reclassified from accumulated other comprehensive income (loss)	6.7			41.8			(1.5		)	—			—			47.0
Net current period other comprehensive income (loss)	(3.9		)	139.2			3.5			5.5			(67.8		)	76.5
Balance, December 31, 2018	$	(4.0	)	$	34.7		$	3.5		$	(31.3	)	$	(243.3	)	$	(240.4	)



(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 Hedge, Net of Tax		Unfunded Status of Postretirement Benefit Plans, net of tax			Currency Translation Adjustments			Total
Balance, December 31, 2016	$	(10.8	)	$	57.8		$	—	$	(32.7	)	$	(334.2	)	$	(319.9	)
Other comprehensive income (loss) before reclassifications	(3.5		)	(193.8		)	—		(4.1		)	158.7			(42.7		)
Amounts reclassified from accumulated other comprehensive income (loss)	12.7			31.5			—		—			—			44.2
Net current period other comprehensive income (loss)	9.2			(162.3		)	—		(4.1		)	158.7			1.5
Balance, December 31, 2017	$	(1.6	)	$	(104.5	)	$	—	$	(36.8	)	$	(175.5	)	$	(318.4	)

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

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



(In millions)	Income Statement Location	Amounts Reclassified from Accumulated Other Comprehensive Income
		For the Years Ended December 31,
		2019			2018			2017
Gains (losses) on securities available for sale	Other income (expense)	$	4.5		$	(8.5	)	$	(19.5	)
	Income tax benefit (expense)	(0.9		)	1.8			6.8

Gains (losses) on cash flow hedges	Revenues	118.6			(42.5		)	(32.5		)
	Operating expenses	(3.3		)	0.2			0.6
	Other income (expense)	0.3			0.3			0.3
	Income tax benefit (expense)	(0.6		)	0.2			0.1

Gains (losses) on net investment hedge	Other Income (expense)	7.0			1.5			—

Total reclassifications, net of tax		$	125.6		$	(47.0	)	$	(44.2	)

Property, Plant and Equipment (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 01, 2019
Property, Plant and Equipment
Depreciation expense	$ 190.6	$ 269.4	$ 266.3
Interest Costs Capitalized	68.8	54.0	$ 30.7
Construction in progress	2,084.4	1,758.5
Solothurn
Property, Plant and Equipment
Construction in progress	$ 1,900.0	$ 1,600.0
Denmark Manufacturing Operations
Property, Plant and Equipment
Property, plant and equipment sold to Fujifilm				$ 631.5
Building
Property, Plant and Equipment
Property, plant and equipment sold to Fujifilm				312.5
Machinery and Equipment
Property, Plant and Equipment
Property, plant and equipment sold to Fujifilm				$ 287.3

Quarterly Financial Data (Unaudited) (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Selected Quarterly Financial Information [Abstract]

Product Revenues

$ 3,671.3

$ 3,600.1

$ 3,616.7

$ 3,489.8

$ 3,526.3

$ 3,439.0

$ 3,356.5

$ 3,131.1

$ 14,377.9

$ 13,452.9

$ 12,273.9

Gross Profit

^[1]

3,224.2

3,170.1

3,140.4

2,887.8

3,037.8

2,978.2

2,935.5

2,685.1

12,422.5

11,636.6

Net income

1,439.7

1,545.9

1,494.1

1,408.8

944.9

1,442.9

915.0

1,171.2

5,888.5

4,474.0

2,670.1

Net income attributable to Biogen Idec Inc

$ 1,439.7

$ 1,545.9

$ 1,494.1

$ 1,408.8

$ 946.8

$ 1,444.4

$ 866.6

$ 1,172.9

$ 5,888.5

$ 4,430.7

$ 2,539.1

Basic earnings per share attributable to Biogen Inc.

$ 8.10

$ 8.40

$ 7.85

$ 7.17

$ 4.74

$ 7.17

$ 4.18

$ 5.55

$ 31.47

$ 21.63

$ 11.94

Diluted earnings per share attributable to Biogen Inc.

$ 8.08

$ 8.39

$ 7.85

$ 7.15

$ 4.73

$ 7.15

$ 4.18

$ 5.54

$ 31.42

$ 21.58

$ 11.92

Basic earnings per share attributable to Biogen Inc.

177.8

184.0

190.3

196.6

199.8

201.4

207.1

211.4

187.1

204.9

212.6

Diluted earnings per share attributable to Biogen Inc.

178.2

184.2

190.4

197.0

200.3

201.9

207.3

211.7

187.4

205.3

213.0

Revenues from anti-cd20 therapeutic programs

Selected Quarterly Financial Information [Abstract]

Product Revenues

$ 600.8

$ 595.8

$ 576.4

$ 517.4

$ 534.9

$ 511.7

$ 490.4

$ 443.2

$ 2,290.4

$ 1,980.2

$ 1,559.2

Other revenue

Selected Quarterly Financial Information [Abstract]

Product Revenues

145.7

109.6

160.0

292.4

165.7

147.2

108.6

164.4

707.7

585.9

360.0

Product, net

Selected Quarterly Financial Information [Abstract]

Product Revenues

$ 2,924.8

$ 2,894.7

$ 2,880.3

$ 2,680.0

$ 2,825.7

$ 2,780.1

$ 2,757.5

$ 2,523.5

$ 11,379.8

$ 10,886.8

$ 10,354.7

[1]	(1) Gross profit is calculated as total revenues less cost of sales, excluding amortization and impairment of acquired intangible assets

Share Repurchases (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2016
Class of Stock [Line Items]
Preferred stock, shares authorized	8,000
Payments for repurchase of common stock	$ 5,868.3	$ 4,352.6	$ 1,365.4
Series A
Class of Stock [Line Items]
Preferred stock, shares authorized	1,750
Series X junior participating
Class of Stock [Line Items]
Preferred stock, shares authorized	1,000
Undesignated
Class of Stock [Line Items]
Preferred stock, shares authorized	5,250
December 2019 Share Repurchase Program [Member]
Class of Stock [Line Items]
Authorized amount of share repurchases	$ 5,000.0
March 2019 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases				$ 5,000.0
Repurchase of common stock, at cost, shares	14,700
Payments for repurchase of common stock	$ 3,700.0
2018 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases					$ 3,500.0
Repurchase of common stock, at cost, shares	8,900	4,300
Payments for repurchase of common stock	$ 2,100.0	$ 1,400.0
2016 Share Repurchase Program
Class of Stock [Line Items]
Authorized amount of share repurchases						$ 5,000.0
Repurchase of common stock, at cost, shares		10,500	3,700
Payments for repurchase of common stock		$ 3,000.0	$ 1,000.0

Intangible Assets and Goodwill

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets and Goodwill

Intangible Assets

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



		As of December 31, 2019							As of December 31, 2018
(In millions)	Estimated Life	Cost		Accumulated Amortization			Net		Cost		Accumulated Amortization			Net
Completed technology	4-28 years	$	7,379.3	$	(4,881.4	)	$	2,497.9	$	7,187.3	$	(4,607.3	)	$	2,580.0
In-process research and development	Indefinite until commercialization	965.5		—			965.5		476.0		—			476.0
Trademarks and trade names	Indefinite	64.0		—			64.0		64.0		—			64.0
Total intangible assets		$	8,408.8	$	(4,881.4	)	$	3,527.4	$	7,727.3	$	(4,607.3	)	$	3,120.0

Amortization and Impairments

Amortization and impairments of acquired intangible assets totaled $489.9 million, $747.3 million and $814.7 million for the years ended December 31, 2019, 2018 and 2017, respectively. Amortization of acquired intangible assets, excluding impairment charges, totaled $274.0 million, $381.2 million and $455.3 million for the years ended December 31, 2019, 2018 and 2017, 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, primarily due to prior year impairments.

For the year ended December 31, 2019, amortization and impairments of acquired intangible assets reflects the impact of a $215.9 million impairment charge to reduce the fair value of IPR&D assets associated with BG00011 (STX-100) to zero, as discussed below.

Amortization and impairments of acquired intangible assets for the year ended December 31, 2018, reflects the impact of impairment charges related to certain IPR&D assets associated with our vixotrigine program totaling $189.3 million, as discussed below.

Amortization and impairments of acquired intangible assets for the years ended December 31, 2018 and 2017, reflect the impact of impairment charges of $176.8 million and $328.2 million, respectively, related to our intangible

assets associated with our U.S. license to Forward Pharma's intellectual property, including Forward Pharma's intellectual property related to TECFIDERA.

Completed Technology

Completed technology primarily relates to our acquisition of all remaining rights to TYSABRI from Elan. The net book value of the TYSABRI asset as of December 31, 2019, was $1.8 billion.

Completed technology also includes $155.0 million in milestone payments made to Alkermes Pharma Ireland Limited, a subsidiary of Alkermes plc (Alkermes), following the approval of VUMERITY in the U.S. in October 2019, technology related to our AVONEX product, which we recorded in connection with the merger of Biogen, Inc. and IDEC Pharmaceuticals Corporation in 2003, our rest of world license to Forward Pharma's intellectual property, including Forward Pharma's intellectual property related to TECFIDERA, as discussed below, and other amounts related to our other marketed products and other programs acquired through business combinations.

TECFIDERA License Rights

In January 2017 we entered into a settlement and license agreement among Biogen Swiss Manufacturing GmbH, Biogen International Holding Ltd., Forward Pharma and certain related parties, which was effective as of February 1, 2017. Pursuant to this agreement, we obtained U.S. and rest of world licenses to Forward Pharma's intellectual property, including Forward Pharma's intellectual property related to TECFIDERA. In exchange, we paid Forward Pharma $1.25 billion in cash, of which $795.2 million was recorded within intangible assets in the first quarter of 2017.

We had an intellectual property dispute with Forward Pharma in the U.S. concerning intellectual property related to TECFIDERA.

In March 2017 the U.S. intellectual property dispute was decided in our favor. Forward Pharma appealed to the U.S. Court of Appeals for the Federal Circuit. We evaluated the recoverability of the U.S. asset acquired from Forward Pharma and recorded a $328.2 million impairment charge in the first quarter of 2017 to adjust the carrying value of the acquired U.S. asset to fair value reflecting the impact of the developments in the U.S. legal dispute and continued to amortize the remaining net book value of the U.S. intangible asset in our consolidated statements of income utilizing an economic consumption model. The U.S. Court of Appeals for the Federal Circuit upheld the U.S. Patent and Trademark Office’s March 2017 ruling and in January 2019 denied Forward Pharma's petition for rehearing. We evaluated the recoverability of the U.S. asset based upon these most recent developments and recorded a $176.8 million impairment charge in the fourth quarter of 2018 to reduce the remaining net book value of the U.S. asset to zero.

We have an intellectual property dispute with Forward Pharma in the European Union (E.U.) concerning intellectual property related to TECFIDERA.

In March 2018 the European Patent Office (EPO) revoked Forward Pharma’s European Patent No. 2 801 355. Forward Pharma has filed an appeal to the Technical Boards of Appeal of the EPO and a hearing has been set for June 2020. Based upon our assessment of this ruling, we continue to amortize the remaining net book value of the rest of world intangible asset in our consolidated statements of income utilizing an economic consumption model. The remaining net book value of the TECFIDERA rest of world intangible asset as of December 31, 2019, was $36.1 million.

For additional information on the dispute with Forward Pharma in the E.U., please read Note 20, Litigation, to these consolidated financial statements.

IPR&D Related to Business Combinations

IPR&D represents the fair value assigned to research and development assets that we acquired as part of a business combination and had not yet reached technological feasibility at the date of acquisition. Upon commercialization, we will determine the estimated useful life and amortize these amounts based upon an economic consumption method. The carrying value associated with our IPR&D assets as of December 31, 2019 and 2018, relates to the various IPR&D programs we acquired in connection with our acquisitions of NST, Convergence Pharmaceuticals Holdings Limited (Convergence), Stromedix Inc. (Stromedix) and Biogen International Neuroscience GmbH (BIN) in 2019, 2015, 2012 and 2010, respectively. IPR&D balances include adjustments related to foreign currency exchange rate fluctuations.

An analysis of anticipated lifetime revenues and anticipated development costs is performed annually during our long-range planning cycle, which was most recently updated in the second quarter of 2019. This analysis is based upon certain assumptions that we evaluate on a periodic basis, including anticipated future product sales, the expected impact of changes in the amount of development costs and the probabilities of our programs succeeding, the introduction of new products by our competitors and changes in our commercial and pipeline product candidates.

In connection with our acquisition of NST in June 2019, we acquired IPR&D programs with an estimated fair value of $700.0 million. For additional information on our acquisition of NST, please read Note 2, Acquisitions, to these consolidated financial statements.

BG00011

During the third quarter of 2019 we discontinued the Phase 2b study of BG00011 for the potential treatment of idiopathic pulmonary fibrosis (IPF) due to safety concerns. As a result, we recognized an impairment charge of approximately $215.9 million during the third quarter of 2019 to reduce the fair value of the IPR&D intangible asset to zero. We also adjusted the value of our contingent consideration obligations related to this asset resulting in a gain of $61.2 million in the third quarter of 2019.

Vixotrigine

During the third quarter of 2018 we completed a Phase 2b study of vixotrigine for the potential treatment of painful lumbosacral radiculopathy (PLSR). The study did not meet its primary or secondary efficacy endpoints and we discontinued development of vixotrigine for the potential treatment of PLSR. As a result, we recognized an impairment charge of approximately $60.0 million during the third quarter of 2018 to reduce the fair value of the related IPR&D intangible asset to zero.

In addition, we delayed the initiation of the Phase 3 studies of vixotrigine for the potential treatment of TGN as we awaited the outcome of ongoing interactions with the FDA regarding the design of the Phase 3 studies, a more detailed review of the data from the Phase 2b study of vixotrigine for the potential treatment of PLSR and insights from the Phase 2 study of vixotrigine for the potential treatment of small fiber neuropathy. We reassessed the fair value of the TGN program using reduced expected lifetime revenues, higher expected clinical development costs and lower cumulative probability of success. As a result of that reassessment, we recognized an impairment charge of $129.3 million during the third quarter of 2018 to reduce the fair value of the TGN IPR&D intangible asset to $41.8 million.

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 revenues, costs and probabilities of success.

Estimated Future Amortization of Intangible Assets

Our most recent long-range planning cycle was completed in the second quarter of 2019. Based upon this most recent analysis, the estimated future amortization of acquired intangible assets for the next five years is expected to be as follows:



(In millions)	As of December 31, 2019
2020	$	260.0
2021	220.0
2022	225.0
2023	230.0
2024	220.0

Goodwill

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



	As of December 31,
(In millions)	2019			2018
Goodwill, beginning of year	$	5,706.4		$	4,632.5
Increase to goodwill	117.5			1,080.1
Elimination of goodwill allocated to Hillerød, Denmark manufacturing operations	(69.5		)	—
Other	3.4			(6.2		)
Goodwill, end of year	$	5,757.8		$	5,706.4

The increase to goodwill during 2019 was related to our acquisition of NST. For additional information on our acquisition of NST, please read Note 2, Acquisitions, to these consolidated financial statements.

The increase to goodwill during 2018 was related to $1.2 billion in contingent milestones achieved (exclusive of $119.9 million in tax benefits) and payable to the former shareholders of Fumapharm AG and holders of their rights. In the fourth quarter of 2018 we achieved the $20.0 billion cumulative sales level threshold and accrued the final contingent payment of $300.0 million related to FUMADERM and TECFIDERA (together, the Fumapharm Products), which was paid in the first quarter of 2019.

The elimination of goodwill represents an allocation based upon the relative fair value of our Hillerød, Denmark manufacturing operations at the divestiture date. In connection with the divestiture of our Hillerød, Denmark manufacturing operations, our remaining goodwill was reviewed for impairment, and based upon this review, no impairments were recognized. For additional information on the divestiture of our Hillerød, Denmark manufacturing operations, please read Note 3, Divestitures, to these consolidated financial statements.

As of December 31, 2019, we had no accumulated impairment losses related to goodwill.

Other includes changes related to foreign currency exchange rate fluctuations.

Leases Leases (Details) - USD ($) $ in Millions	12 Months Ended
Leases Leases (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Operating lease assets	$ 427.0	$ 0.0
Operating lease liability, noncurrent	412.7	0.0
Operating lease liabilities	486.3
Net lease cost	86.7
ASC 842 - Minimum lease payments, 2020	87.6
ASC 842 - Minimum lease payments, 2021	81.5
ASC 842 - Minimum lease payments, 2022	75.7
ASC 842 - Minimum lease payments, 2023	72.5
ASC 842 - Minimum lease payments, 2024	69.0
ASC 842 - Minimum lease payments, thereafter	158.3
Total lease payments	544.6
Less: interest	$ 58.3
ASC 840 - Minimum lease payments, 2019		87.0
ASC 840 - Minimum lease payments, 2020		80.7
ASC 840 - Minimum lease payments, 2021		75.9
ASC 840 - Minimum lease payments, 2022		71.7
ASC 840 - Minimum lease payments, 2023		71.0
ASC 840 - Minimum lease payments, thereafter		215.3
ASC 840 - Minimum lease payments, total		601.6
ASC 840 - Sublease income, 2019		(26.8)
ASC 840 - Sublease income, 2020		(25.6)
ASC 840 - Sublease income, 2021		(23.7)
ASC 840 - Sublease income, 2022		(24.0)
ACS 840 - Sublease income, 2023		(24.3)
ASC 840 - Sublease income, thereafter		(58.4)
ASC 840 - Sublease income, total		(182.8)
ASC 840 - Net minimum lease payments, 2019		60.2
ASC 840 - Net minimum lease payments, 2020		55.1
ASC 840 - Net minimum lease payments, 2021		52.2
ASC 840 - Net minimum lease payments, 2022		47.7
ASC 840 - Net minimum lease payments, 2023		46.7
ASC 840 - Net minimum lease payments, thereafter		156.9
ASC 840 - Net minimum lease payments, total		$ 418.8
Operating Lease, Weighted Average Remaining Lease Term	7 years 25 days
Operating Lease, Weighted Average Discount Rate, Percent	3.20%
Operating Lease, Payments	$ 93.8
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	35.9
Operating lease assets [Member]
Operating lease assets	427.0
Accrued expenses and other
Operating lease liability, current	73.6
Long-term operating lease liabilities [Member]
Operating lease liability, noncurrent	412.7
Research and development
Operating lease cost	6.7
Variable lease cost	1.2
Selling, General and Administrative Expenses
Operating lease cost	84.6
Variable lease cost	23.7
Sublease income	(25.6)
Other income (expense)
Sublease income	$ (3.9)

Financial Instruments (Details Textual 2) $ in Millions, ₩ in Billions	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 KRW (₩)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 KRW (₩)	Dec. 31, 2018 KRW (₩)	Feb. 29, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Business Acquisition [Line Items]
Sale of Ionis common stock			$ 479.3	$ 0.0	$ 0.0
Payments to increase investment in Samsung Bioepis			0.0	676.6	$ 0.0
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio	$ 676.3		393.9	$ 676.3
Ionis Pharmaceuticals
Business Acquisition [Line Items]
Sale of Ionis common stock			$ 382.0
Samsung Bioepis
Business Acquisition [Line Items]
Samsung Bioepis, ownership percentage before additional purchase transaction	5.00%			5.00%			5.00%
Samsung Bioepis, ownership percentage			49.90%			49.90%		15.00%	15.00%
Payments to increase investment in Samsung Bioepis	$ 676.6	₩ 759.5
Investment in Samsung Bioepis	$ 680.6		$ 580.2	$ 680.6		₩ 670.8	₩ 759.5	$ 45.0	₩ 49.5

Earnings per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Earnings per Share

Basic and diluted earnings per share are calculated as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Numerator:
Net income attributable to Biogen Inc.	$	5,888.5	$	4,430.7	$	2,539.1
Denominator:
Weighted average number of common shares outstanding	187.1		204.9		212.6
Effect of dilutive securities:
Stock options and employee stock purchase plan	—		—		0.1
Time-vested restricted stock units	0.2		0.3		0.2
Market stock units	0.1		0.1		0.1
Performance stock units settled in stock	—		—		—
Dilutive potential common shares	0.3		0.4		0.4
Shares used in calculating diluted earnings per share	187.4		205.3		213.0

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, 2019, 2018 and 2017, reflects, on a weighted average basis, the repurchase of approximately 23.6 million shares, 14.8 million shares and 3.7 million shares of our common stock, respectively, under our March 2019, 2018 and 2016 Share Repurchase Programs.

Indebtedness (Details 1) $ in Millions	Dec. 31, 2019 USD ($)
Total debt maturities
2020	$ 1,500.0
2021	0.0
2022	1,000.0
2023	0.0
2024	0.0
2025 and thereafter	3,500.0
Total	$ 6,000.0

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

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, 2019 (In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	2,541.1	$	—	$	2,541.1	$	—
Marketable debt securities:
Corporate debt securities	1,695.1		—		1,695.1		—
Government securities	1,013.9		—		1,013.9		—
Mortgage and other asset backed securities	261.3		—		261.3		—
Marketable equity securities	337.5		7.9		329.6		—
Derivative contracts	43.8		—		43.8		—
Plan assets for deferred compensation	27.7		—		27.7		—
Total	$	5,920.4	$	7.9	$	5,912.5	$	—
Liabilities:
Derivative contracts	$	8.3	$	—	$	8.3	$	—
Contingent consideration obligations	346.1		—		—		346.1
Total	$	354.4	$	—	$	8.3	$	346.1



As of December 31, 2018 (In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	705.5	$	—	$	705.5	$	—
Marketable debt securities:
Corporate debt securities	2,459.2		—		2,459.2		—
Government securities	969.6		—		969.6		—
Mortgage and other asset backed securities	260.5		—		260.5		—
Marketable equity securities	615.4		51.7		563.7		—
Derivative contracts	66.9		—		66.9		—
Plan assets for deferred compensation	25.4		—		25.4		—
Total	$	5,102.5	$	51.7	$	5,050.8	$	—
Liabilities:
Derivative contracts	$	24.6	$	—	$	24.6	$	—
Contingent consideration obligations	409.8		—		—		409.8
Total	$	434.4	$	—	$	24.6	$	409.8

There have been no changes in valuation techniques or transfers between fair value measurement levels during the years ended December 31, 2019 and 2018. The fair value of Level 2 instruments classified as cash equivalents, marketable debt securities and our marketable equity security investment in Ionis Pharmaceuticals, Inc. (Ionis) were determined through third-party pricing services or an option pricing valuation model. For additional information on our collaboration arrangements with Ionis, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements. For a description of our validation procedures related to prices provided by third-party pricing services and our option pricing valuation model, please read Note 1, Summary of Significant Accounting Policies - Fair Value Measurements, to these consolidated financial statements.

Debt Instruments

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



	As of December 31,
(In millions)	2019		2018
2.900% Senior Notes due September 15, 2020	$	1,509.6	$	1,489.5
3.625% Senior Notes due September 15, 2022	1,038.9		1,000.4
4.050% Senior Notes due September 15, 2025	1,897.2		1,745.1
5.200% Senior Notes due September 15, 2045	2,107.9		1,802.6
Total	$	6,553.6	$	6,037.6

Contingent Consideration Obligations

In connection with our acquisitions of Convergence, Stromedix and BIN in 2015, 2012 and 2010, respectively, 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 includes Level 3 measurements:



	As of December 31,
(In millions)	2019			2018
Fair value, beginning of year	$	409.8		$	523.6
Changes in fair value	(63.7		)	(12.3		)
Payments and other	—			(101.5		)
Fair value, end of year	$	346.1		$	409.8

As of December 31, 2019 and 2018, approximately $197.7 million and $265.0 million, respectively, 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 with the remaining balance reflected as a component of accrued expenses and other.

For the year ended December 31, 2019, changes in the fair value of our contingent consideration obligations were primarily due to the discontinuation of the Phase 2b study of BG00011 for the potential treatment of IPF resulting in a reduction of our contingent consideration obligations of $61.2 million, partially offset by changes in the probability and expected timing of achievement of certain developmental milestones, a decrease in interest rates used to revalue our contingent consideration liabilities and the passage of time.

For the year ended December 31, 2018, changes in the fair value of our contingent consideration obligations were primarily due to delays in the expected timing of achievement of milestones related to the TGN program and an increase in discount rates used to revalue our contingent consideration liabilities, partially offset by the passage of time. For the year ended December 31, 2018, payments and other reflects an $81.5 million milestone payment made to the former shareholders of Stromedix.

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 including estimated revenues and probabilities of success. 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, 2019 and 2018, the fair value of this contingent consideration obligation was $244.6 million and $246.6 million, respectively. Our most recent valuation was determined based upon net cash flow projections of $400.0 million, probability weighted and discounted using a rate of 2.1%, which is a measure of the credit risk associated with settling the liability.

For 2019 compared to 2018, the net decrease in our contingent consideration obligation was primarily due to changes in the expected timing and probabilities of success related to the achievement of certain developmental milestones, partially offset by a decrease in discount rates used to revalue our contingent consideration liabilities and the passage of time. Accrued expenses and other in our consolidated balances sheets include $148.5 million as we expect to make the payment within one year.

Stromedix Inc.

In connection with our acquisition of Stromedix in March 2012 we recorded a contingent consideration obligation of $122.2 million. During the third quarter of 2019 we discontinued the Phase 2b study of BG00011 for the potential treatment of IPF due to safety concerns. As a result, we adjusted the fair value of this contingent consideration obligation to zero, resulting in a gain of $61.2 million in the third quarter of 2019. As of December 31, 2018, the fair value of this contingent consideration obligation was $83.0 million.

Biogen Idec International Neuroscience GmbH

In connection with our acquisition of BIN in December 2010 we recorded a contingent consideration obligation of $81.2 million. As of December 31, 2019 and 2018, the fair value of this contingent consideration obligation was $101.5 million and $80.2 million, respectively. Our most recent valuation was determined based upon net cash outflow projections of $335.0 million, probability weighted and discounted using a rate of 2.3%, which is a measure of the credit risk associated with settling the liability.

For 2019 compared to 2018, the net increase in our contingent consideration obligation was primarily due to changes in the expected timing and probabilities of success related to the achievement of certain developmental milestones, a decrease in discount rates used to revalue our contingent consideration liabilities and the passage of time. No amounts are reflected as a current liability in our consolidated balance sheets at December 31, 2019, as we do not expect to make a payment in the next year.

Acquired IPR&D

The fair values of the acquired IPR&D assets were based on a probability-adjusted discounted cash flow calculation using Level 3 fair value measurements and inputs including estimated revenues and probabilities of success. These assets are tested for impairment annually until commercialization, after which time the acquired

IPR&D will be amortized over its estimated useful life using the economic consumption method. In connection with our acquisition of Stromedix, we recognized a $219.2 million acquired IPR&D intangible asset. During the third quarter of 2019 we discontinued the Phase 2b study of BG00011 for the potential treatment of IPF due to safety concerns and recognized an impairment charge of $215.9 million to reduce the fair value of the IPR&D intangible asset to zero. In connection with our acquisition of Convergence we recognized a $424.6 million acquired IPR&D intangible asset. During the third quarter of 2018 we recognized impairment charges related to certain IPR&D assets associated with our vixotrigine program totaling $189.3 million. For additional information on our IPR&D intangible assets, including a discussion of our most significant assumptions, please read Note 6, Intangible Assets and Goodwill, 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 (Details 1) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Marketable Debt and Equity Securities
Debt securities, amortized cost	$ 2,965.0	$ 3,694.0
Debt securities, gross unrealized gains	6.0	1.3
Debt securities, gross unrealized losses	0.7	6.0
Debt securities, fair value	2,970.3	3,689.3
Corporate debt securities Current
Marketable Debt and Equity Securities
Debt securities, amortized cost	1,057.2	1,608.4
Debt securities, gross unrealized gains	1.0	0.0
Debt securities, gross unrealized losses	0.0	0.9
Debt securities, fair value	1,058.2	1,607.5
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Debt securities, amortized cost	633.9	854.9
Debt securities, gross unrealized gains	3.0	0.7
Debt securities, gross unrealized losses	0.0	3.9
Debt securities, fair value	636.9	851.7
Government securities Current
Marketable Debt and Equity Securities
Debt securities, amortized cost	502.9	706.1
Debt securities, gross unrealized gains	0.4	0.1
Debt securities, gross unrealized losses	0.0	0.4
Debt securities, fair value	503.3	705.8
Government securities Non-current
Marketable Debt and Equity Securities
Debt securities, amortized cost	510.1	264.0
Debt securities, gross unrealized gains	0.8	0.1
Debt securities, gross unrealized losses	0.3	0.3
Debt securities, fair value	510.6	263.8
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Debt securities, amortized cost	0.7	0.1
Debt securities, gross unrealized gains	0.0	0.0
Debt securities, gross unrealized losses	0.0	0.0
Debt securities, fair value	0.7	0.1
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Debt securities, amortized cost	260.2	260.5
Debt securities, gross unrealized gains	0.8	0.4
Debt securities, gross unrealized losses	0.4	0.5
Debt securities, fair value	260.6	260.4
Marketable equity securities
Marketable Debt and Equity Securities
Marketable equity securities, amortized cost	218.4	496.2
Marketable equity securities, gross unrealized gains	132.1	127.7
Marketable equity securities, gross unrealized losses	13.0	8.5
Marketable equity securities, fair value	$ 337.5	$ 615.4

Share-Based Payments (Details 11) - USD ($) $ in Millions	12 Months Ended
Share-Based Payments (Details 11) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP	6,200,000
2015 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP	204,000	170,000	167,000
Cash received under ESPP	$ 40.4	$ 40.5	$ 39.8

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Minimum rental commitments under non-cancelable leases



(In millions)	2019			2020			2021			2022			2023			Thereafter			Total
Minimum lease payments	$	87.0		$	80.7		$	75.9		$	71.7		$	71.0		$	215.3		$	601.6
Less: income from subleases⁽¹⁾	(26.8		)	(25.6		)	(23.7		)	(24.0		)	(24.3		)	(58.4		)	(182.8		)
Net minimum lease payments	$	60.2		$	55.1		$	52.2		$	47.7		$	46.7		$	156.9		$	418.8

(1)

Represents sublease income expected to be received for the vacated manufacturing facility in Cambridge, MA, the vacated portion of our Weston, MA facility and other facilities throughout the world.

Intangible Assets and Goodwill (Tables)

12 Months Ended

Dec. 31, 2019

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, 2019							As of December 31, 2018
(In millions)	Estimated Life	Cost		Accumulated Amortization			Net		Cost		Accumulated Amortization			Net
Completed technology	4-28 years	$	7,379.3	$	(4,881.4	)	$	2,497.9	$	7,187.3	$	(4,607.3	)	$	2,580.0
In-process research and development	Indefinite until commercialization	965.5		—			965.5		476.0		—			476.0
Trademarks and trade names	Indefinite	64.0		—			64.0		64.0		—			64.0
Total intangible assets		$	8,408.8	$	(4,881.4	)	$	3,527.4	$	7,727.3	$	(4,607.3	)	$	3,120.0

Estimated future amortization of intangible assets

Based upon this most recent analysis, the estimated future amortization of acquired intangible assets for the next five years is expected to be as follows:



(In millions)	As of December 31, 2019
2020	$	260.0
2021	220.0
2022	225.0
2023	230.0
2024	220.0

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)	2019			2018
Goodwill, beginning of year	$	5,706.4		$	4,632.5
Increase to goodwill	117.5			1,080.1
Elimination of goodwill allocated to Hillerød, Denmark manufacturing operations	(69.5		)	—
Other	3.4			(6.2		)
Goodwill, end of year	$	5,757.8		$	5,706.4

Share-Based Payments (Details 4) - Market stock units - $ / shares

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Market stock units activity

Beginning Balance, Unvested, Shares

180,000

Beginning Balance, Weighted Average Grant Date Fair Value

$ 371.32

Shares, Granted

^[1]

147,000

Weighted Average Grant Date Fair Value, Granted

$ 378.08

^[1]

$ 378.85

$ 382.59

Shares, Vested

(101,000)

Weighted Average Grant Date Fair Value, Vested

$ 356.71

Shares, Forfeited

(43,000)

Weighted Average Grant Date Fair Value, Forfeited

$ 388.68

Ending Balance, Unvested, Shares

183,000

180,000

Ending Balance, Weighted Average Grant Date Fair Value

$ 378.09

$ 371.32

[1]

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

e recognize revenues 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 revenues following the five-step model prescribed under the 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 revenues when (or as) we satisfy the performance obligation.

Product Revenues

Reserves for Discounts and Allowances

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

•


•	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.


•	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.

separable benefit and fair value for these services we classify these payments in selling, general and administrative expenses.

Revenues from Anti-CD20 Therapeutic Programs

Revenues from anti-CD20 therapeutic programs consist of:


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


(ii)	other revenues from anti-CD20 therapeutic programs, which primarily consist of our share of pre-tax co-promotion profits on RITUXAN in Canada and royalty revenues on sales of OCREVUS.

For additional information on our relationship with Genentech, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Other Revenues

Royalty Revenues

Collaborative and Other Relationships

Other Corporate Revenues

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.

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.

income on these receivables, which is recorded as a component of other income (expense), net in our consolidated statements of income.

Concentration of Credit Risk

Marketable Securities and Other Investments

Marketable Debt Securities

Marketable Equity Securities and Venture Capital Funds

Non-Marketable Equity Securities

Evaluating Marketable Debt Securities for Other-than-Temporary Impairments

Equity Method of Accounting

Inventory

Capitalization of Inventory Costs

Obsolescence and Unmarketable Inventory

cost or its estimated net realizable value. Amounts written-down due to unmarketable inventory are charged to cost of sales.

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

For additional information on the adoption of the new leasing standards, please read Note 11, Leases, to these consolidated financial statements.

Intangible Assets

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

Goodwill

Impairment of Long-Lived Assets

Contingent Consideration

Derivative Instruments and Hedging Activities

Cash Flow and Fair Value Derivative Instruments

Net Investment Derivative Instruments

For additional information on our derivative instruments and hedging activities, please read Note 9, Derivative Instruments, to these consolidated financial statements.

Translation of Foreign Currencies

Royalty Cost of Sales

Accounting for Share-Based Compensation

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

Research and Development Expenses

Selling, General and Administrative Expenses

Advertising costs are expensed as incurred. For the years ended December 31, 2019, 2018 and 2017, advertising costs totaled $79.2 million, $90.2 million and $75.2 million, respectively.

Income Taxes

Contingencies

Earnings per Share

New Accounting Pronouncements

rom 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.

Leases

Credit Losses

Debt Securities

Fair Value Measurements

Derivative Instruments and Hedging Activities

Collaborative Arrangements

•


•	Adds unit-of-account guidance to ASC 808, Collaborative Arrangements, to align with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606; and


•	Precludes a company from presenting transactions with collaborative arrangement participants that are not directly related to sales to third parties with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer.

Share-Based Payments (Details 6) - Cash settled performance units	12 Months Ended
	Dec. 31, 2019 shares
Cash settled performance shares
Beginning Balance, Unvested, Shares	50,000,000
Shares, Granted	0
Shares, Vested	(33,000,000)
Shares, Forfeited	(4,000,000)
Ending Balance, Unvested, Shares	13,000,000

Derivative Instruments Interest Rate Swap (Details 2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 1,892.4	$ 2,239.1
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	793.8	735.1
Foreign Exchange Contract \| Other current assets \| Not Designated as Hedging Instrument
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative assets	8.0	1.1
Foreign Exchange Contract \| Accrued expenses and other \| Not Designated as Hedging Instrument
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative liabilities	2.4	3.2
Interest rate swap \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount			$ 675.0
Euro \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,892.4	1,701.4
British pound sterling \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0.0	215.3
Swiss francs \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0.0	131.4
Canadian dollar \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0.0	92.2
Japan, Yen \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0.0	98.8
Cash Flow Hedge \| Foreign Exchange Contract \| Other current assets
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative assets	33.8	65.8
Cash Flow Hedge \| Foreign Exchange Contract \| Accrued expenses and other
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative liabilities	2.0	6.9
Cash Flow Hedge \| Foreign Exchange Contract \| Other long-term liabilities
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative liabilities	1.7	0.0
Net Investment Hedge \| Foreign Exchange Contract \| Other current assets
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative assets	2.0	0.0
Fair Value Hedge \| Interest rate swap \| Accrued expenses and other
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative liabilities	2.3	0.0
Fair Value Hedge \| Interest rate swap \| Other long-term liabilities
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Derivative liabilities	$ 0.0	$ 14.5

Share-Based Payments (Details 3) - USD ($) $ in Millions	12 Months Ended
Share-Based Payments (Details 3) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax benefit and cash received from stock option
Tax benefit realized for stock options	$ 2.5	$ 2.2	$ 3.4
Cash received from the exercise of stock options	$ 0.4	$ 0.8	$ 0.7

Share-Based Payments (Details 1) - USD ($) $ in Millions	12 Months Ended
Share-Based Payments (Details 1) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of share based compensation expense associated with different programs
Share-based compensation expense	$ 191.2	$ 168.7		$ (138.1)
Subtotal	225.4	181.6	$ 169.7
Capitalized share-based compensation costs	(8.9)	(11.5)	(9.6)
Share-based compensation expense included in total costs and expenses	216.5	170.1	160.1
Market stock units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	30.4	27.2	22.4
Time-vested restricted stock units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	134.0	126.6	107.3
Cash settled performance units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	0.7	7.8	18.4
Performance Units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	1.6	3.1	12.3
Performance stock units settled in stock
Summary of share based compensation expense associated with different programs
Share-based compensation expense	15.5	4.7	0.0
Performance stock units settled in cash
Summary of share based compensation expense associated with different programs
Share-based compensation expense	5.5	1.7	0.0
Employee stock purchase plan
Summary of share based compensation expense associated with different programs
Share-based compensation expense	11.5	10.5	9.3
Nightstar \| Share-based Payment Arrangement, Option
Summary of share based compensation expense associated with different programs
Fair-value post-combination equity compensation	$ 26.2	$ 0.0	$ 0.0

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

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 90 days from the date of purchase included in cash and cash equivalents in our consolidated balance sheets:



	As of December 31,
(In millions)	2019		2018
Commercial paper	$	384.4	$	231.2
Overnight reverse repurchase agreements	368.8		—
Money market funds	1,628.5		279.5
Short-term debt securities	159.4		194.8
Total	$	2,541.1	$	705.5

Marketable securities including strategic investments

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



As of December 31, 2019 (In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities
Current	$	1,057.2	$	1.0	$	—		$	1,058.2
Non-current	633.9		3.0		—			636.9
Government securities
Current	502.9		0.4		—			503.3
Non-current	510.1		0.8		(0.3		)	510.6
Mortgage and other asset backed securities
Current	0.7		—		—			0.7
Non-current	260.2		0.8		(0.4		)	260.6
Total marketable debt securities	$	2,965.0	$	6.0	$	(0.7	)	$	2,970.3
Marketable equity securities, non-current	$	218.4	$	132.1	$	(13.0	)	$	337.5



As of December 31, 2018 (In millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities
Current	$	1,608.4	$	—	$	(0.9	)	$	1,607.5
Non-current	854.9		0.7		(3.9		)	851.7
Government securities
Current	706.1		0.1		(0.4		)	705.8
Non-current	264.0		0.1		(0.3		)	263.8
Mortgage and other asset backed securities
Current	0.1		—		—			0.1
Non-current	260.5		0.4		(0.5		)	260.4
Total marketable debt securities	$	3,694.0	$	1.3	$	(6.0	)	$	3,689.3
Marketable equity securities, non-current	$	496.2	$	127.7	$	(8.5	)	$	615.4

Summary of contractual maturities: Available-for-sale securities

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



	As of December 31, 2019				As of December 31, 2018
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	1,562.2	$	1,560.8	$	2,313.4	$	2,314.6
Due after one year through five years	1,234.5		1,230.4		1,232.7		1,235.9
Due after five years	173.6		173.8		143.2		143.5
Total marketable debt securities	$	2,970.3	$	2,965.0	$	3,689.3	$	3,694.0

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)	2019		2018		2017
Proceeds from maturities and sales	$	6,007.0	$	9,173.7	$	5,565.9
Realized gains	$	6.0	$	3.2	$	3.0
Realized losses	$	1.5	$	11.7	$	22.4

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2019	Feb. 04, 2020	Jun. 30, 2019
Cover page.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
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
Entity Shell Company	false
Entity Public Float			$ 43,010,112,437
Entity Common Stock, Shares Outstanding		174,064,011
Entity Central Index Key	0000875045
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

Segment Information

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

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 Chief Executive Officer (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 revenues, other revenues and long-lived assets by geographic area are presented below. Revenues are 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, 2019 (In millions)	U.S.		Europe		Asia		Other		Total
Product revenues from external customers	$	6,713.8	$	3,794.5	$	320.3	$	551.2	$	11,379.8
Revenues from anti-CD20 therapeutic programs	$	2,211.9	$	0.2	$	—	$	78.3	$	2,290.4
Other revenues from external customers	$	585.8	$	9.7	$	112.2	$	—	$	707.7
Long-lived assets	$	1,493.2	$	2,162.9	$	6.2	$	12.0	$	3,674.3

December 31, 2018 (In millions)	U.S.		Europe		Asia		Other		Total
Product revenues from external customers	$	6,800.5	$	3,370.3	$	281.2	$	434.8	$	10,886.8
Revenues from anti-CD20 therapeutic programs	$	1,903.4	$	0.2	$	—	$	76.6	$	1,980.2
Other revenues from external customers	$	457.0	$	32.7	$	96.2	$	—	$	585.9
Long-lived assets	$	1,152.7	$	2,442.8	$	3.9	$	1.8	$	3,601.2

December 31, 2017 (In millions)	U.S.		Europe		Asia		Other		Total
Product revenues from external customers	$	7,017.1	$	2,844.8	$	160.1	$	332.7	$	10,354.7
Revenues from anti-CD20 therapeutic programs	$	1,475.6	$	0.6	$	—	$	83.0	$	1,559.2
Other revenues from external customers	$	249.5	$	67.8	$	42.7	$	—	$	360.0
Long-lived assets	$	1,226.9	$	1,948.2	$	5.2	$	2.1	$	3,182.4

Other

As of December 31, 2019, 2018 and 2017, approximately $2,028.8 million, $1,748.5 million and $1,215.7 million, respectively, of our long-lived assets were related to the construction of our large-scale biologics manufacturing facility in Solothurn, Switzerland.

In August 2019 we completed the sale of all of the outstanding shares of our subsidiary that owned our biologics manufacturing operations in Hillerød, Denmark to FUJIFILM. As of December 31, 2018 and 2017, approximately $646.5 million and $707.1 million, respectively, of our long-lived assets were related to our manufacturing facility in Hillerød, Denmark.

For additional information on our large-scale biologics manufacturing facility in Solothurn, Switzerland, please read Note 10, Property, Plant and Equipment, to these consolidated financial statements. For additional information on the divestiture of our Hillerød, Denmark manufacturing operations, please read Note 3, Divestitures, to these consolidated financial statements.

Equity

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

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 2019, 2018 and 2017.

Common Stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2019, 2018 and 2017:

As of December 31, 2019

As of December 31, 2018

As of December 31, 2017

(In millions)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000.0

198.0

174.2

1,000.0

221.0

197.2

1,000.0

235.3

211.5

Share Repurchases

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). Our December 2019 Share Repurchase Program does not have an expiration date. All share repurchases under our December 2019 Share Repurchase Program will be retired. We did not repurchase shares of our common stock under our December 2019 Share Repurchase Program during the year ended December 31, 2019.

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). Our March 2019 Share Repurchase Program does not have an expiration date. All share repurchases under our March 2019 Share Repurchase Program will be retired. Under our March 2019 Share Repurchase Program, we repurchased and retired approximately 14.7 million shares of our common stock at a cost of approximately $3.7 billion during the year ended December 31, 2019.

In August 2018 our Board of Directors authorized a program to repurchase up to $3.5 billion of our common stock (2018 Share Repurchase Program), which was completed as of June 30, 2019. All share repurchases under our 2018 Share Repurchase Program were retired. Under our 2018 Share Repurchase Program, we repurchased and retired approximately 8.9 million and 4.3 million shares of our common stock at a cost of approximately $2.1 billion and $1.4 billion during the years ended December 31, 2019 and 2018, respectively.

In July 2016 our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (2016 Share Repurchase Program), which was completed as of June 30, 2018. All share repurchases under our

2016 Share Repurchase Program were retired. Under our 2016 Share Repurchase Program, we repurchased and retired approximately 10.5 million and 3.7 million shares of common stock at a cost of approximately $3.0 billion and $1.0 billion during the years ended December 31, 2018 and 2017, respectively.

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:



(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 Hedge, Net of Tax			Unfunded Status of Postretirement Benefit Plans, net of tax			Currency Translation Adjustments			Total
Balance, December 31, 2018	$	(4.0	)	$	34.7		$	3.5		$	(31.3	)	$	(243.3	)	$	(240.4	)
Other comprehensive income (loss) before reclassifications	11.8			88.1			28.6			(1.5		)	103.8			230.8
Amounts reclassified from accumulated other comprehensive income (loss)	(3.6		)	(115.0		)	(7.0		)	—			—			(125.6		)
Net current period other comprehensive income (loss)	8.2			(26.9		)	21.6			(1.5		)	103.8			105.2
Balance, December 31, 2019	$	4.2		$	7.8		$	25.1		$	(32.8	)	$	(139.5	)	$	(135.2	)



(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 Hedge, Net of Tax			Unfunded Status of Postretirement Benefit Plans, net of tax			Currency Translation Adjustments			Total
Balance, December 31, 2017	$	(1.6	)	$	(104.5	)	$	—		$	(36.8	)	$	(175.5	)	$	(318.4	)
Amounts reclassified, net of tax, upon adoption of ASU 2016-01	1.5			—			—			—			—			1.5
Balance, January 1, 2018	(0.1		)	(104.5		)	—			(36.8		)	(175.5		)	(316.9		)
Other comprehensive income (loss) before reclassifications	(10.6		)	97.4			5.0			5.5			(67.8		)	29.5
Amounts reclassified from accumulated other comprehensive income (loss)	6.7			41.8			(1.5		)	—			—			47.0
Net current period other comprehensive income (loss)	(3.9		)	139.2			3.5			5.5			(67.8		)	76.5
Balance, December 31, 2018	$	(4.0	)	$	34.7		$	3.5		$	(31.3	)	$	(243.3	)	$	(240.4	)



(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 Hedge, Net of Tax		Unfunded Status of Postretirement Benefit Plans, net of tax			Currency Translation Adjustments			Total
Balance, December 31, 2016	$	(10.8	)	$	57.8		$	—	$	(32.7	)	$	(334.2	)	$	(319.9	)
Other comprehensive income (loss) before reclassifications	(3.5		)	(193.8		)	—		(4.1		)	158.7			(42.7		)
Amounts reclassified from accumulated other comprehensive income (loss)	12.7			31.5			—		—			—			44.2
Net current period other comprehensive income (loss)	9.2			(162.3		)	—		(4.1		)	158.7			1.5
Balance, December 31, 2017	$	(1.6	)	$	(104.5	)	$	—	$	(36.8	)	$	(175.5	)	$	(318.4	)

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



(In millions)	Income Statement Location	Amounts Reclassified from Accumulated Other Comprehensive Income
		For the Years Ended December 31,
		2019			2018			2017
Gains (losses) on securities available for sale	Other income (expense)	$	4.5		$	(8.5	)	$	(19.5	)
	Income tax benefit (expense)	(0.9		)	1.8			6.8

Gains (losses) on cash flow hedges	Revenues	118.6			(42.5		)	(32.5		)
	Operating expenses	(3.3		)	0.2			0.6
	Other income (expense)	0.3			0.3			0.3
	Income tax benefit (expense)	(0.6		)	0.2			0.1

Gains (losses) on net investment hedge	Other Income (expense)	7.0			1.5			—

Total reclassifications, net of tax		$	125.6		$	(47.0	)	$	(44.2	)

Segment Information (Details Textual) $ in Millions	12 Months Ended
Segment Information (Details Textual) $ in Millions	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenue from External Customer [Line Items]
Long-lived assets related to operations in Denmark	$ 3,674.3	$ 3,601.2	$ 3,182.4
Segment Information (Textual) [Abstract]
Number of reportable segment \| segment	1
Solothurn
Revenue from External Customer [Line Items]
Long-lived assets related to operations in Denmark	$ 2,028.8	1,748.5	1,215.7
DENMARK
Revenue from External Customer [Line Items]
Long-lived assets related to operations in Denmark		$ 646.5	$ 707.1

Collaborative and Other Relationships - AbbVie (Details 2) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative arrangements and non-collaborative arrangement transactions
Product Revenues	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
Costs and expenses									7,335.3	7,564.3	6,928.1
Product, net
Collaborative arrangements and non-collaborative arrangement transactions
Product Revenues	$ 2,924.8	$ 2,894.7	$ 2,880.3	$ 2,680.0	$ 2,825.7	$ 2,780.1	$ 2,757.5	$ 2,523.5	11,379.8	10,886.8	10,354.7
Product, net \| U.S
Collaborative arrangements and non-collaborative arrangement transactions
Product Revenues									$ 6,713.8	$ 6,800.5	$ 7,017.1

Financial Instruments (Details 2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Summary of Contractual Maturities: Available-for-Sale Securities
Due in one year or less, Estimated Fair Value	$ 1,562.2	$ 2,313.4
Due in one year or less, Amortized Cost	1,560.8	2,314.6
Due after one year through five years, Estimated Fair Value	1,234.5	1,232.7
Due after one year through five years, Amortized Cost	1,230.4	1,235.9
Due after five years, Estimated Fair Value	173.6	143.2
Due after five years, Amortized Cost	173.8	143.5
Debt securities, amortized cost	2,965.0	3,694.0
Debt Securities, Available-for-sale	$ 2,970.3	$ 3,689.3

Share-Based Payments (Details 2)	12 Months Ended
Share-Based Payments (Details 2)	Dec. 31, 2019 $ / shares shares
Stock Option Activity
Beginning Balance, Outstanding shares \| shares	27,000
Beginning Balance, Weighted Average Exercise Price \| $ / shares	$ 53.82
Shares, Granted \| shares	0
Weighted Average Exercise Price, Granted \| $ / shares	$ 0
Shares, Exercised \| shares	(15,000)
Weighted Average Exercise Price, Exercised \| $ / shares	$ 50.03
Shares, Cancelled \| shares	0
Weighted Average Exercise Price, Cancelled \| $ / shares	$ 0
Ending Balance, Outstanding shares \| shares	12,000
Ending Balance, Weighted Average Exercise Price \| $ / shares	$ 58.46

Other Consolidated Financial Statement Detail (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Securities, FV-NI, Gain (Loss)	$ 200.1	$ 127.9	$ (19.8)
Equity Securities, FV-NI, Realized Gain (Loss)	50.0	(0.6)	0.0
Equity Securities, FV-NI, Unrealized Gain (Loss)	150.1	128.5	(19.8)
Cash Paid During the Year
Interest	244.2	243.2	281.7
Income taxes	1,064.5	1,007.1	1,066.4
Other Nonoperating Income (Expense) [Abstract]
Interest income	120.0	112.5	78.5
Interest expense	187.4	200.6	250.8
Gain (loss) on investments, net	204.7	119.5	(36.3)
Foreign exchange gains (losses), net	(7.0)	(9.9)	6.3
Other income (expense)	(47.0)	(10.5)	(14.7)
Total other income (expense), net	83.3	11.0	(217.0)
Accrued Liabilities, Current [Abstract]
Revenue related reserves for discounts and allowances	1,198.9	1,051.3	$ 761.6	$ 605.5
Employee compensation and benefits	309.1	320.9
Collaboration expenses	281.6	261.6
Royalties and licensing fees	220.9	224.7
Current portion of contingent consideration obligations	148.4	444.8
Accrued construction in progress	78.0	125.2
Other	726.7	609.3
Accrued expenses and other	2,765.8	2,861.2
Other Current Liabilities
Accrued Liabilities, Current [Abstract]
Revenue related reserves for discounts and allowances	$ 1,001.1	$ 874.7

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income attributable to Biogen Inc.	$ 5,888.5	$ 4,430.7	$ 2,539.1
Other comprehensive income:
Unrealized gains (losses) recognized during the period, net of tax	11.8	(10.6)	(3.5)
Less: reclassification adjustment for (gains) losses included in net income, net of tax	(3.6)	6.7	12.7
Unrealized gains (losses) on securities available for sale, net of tax	8.2	(3.9)	9.2
Unrealized gains (losses) recognized during the period, net of tax	88.1	97.4	(193.8)
Less: reclassification adjustment for (gains) losses included in net income, net of tax	(115.0)	41.8	31.5
Unrealized gains (losses) on cash flow hedges, net of tax	(26.9)	139.2	(162.3)
Gains (Losses) on net investment hedge recognized during period	28.6	5.0	0.0
Less: Reclassification of net investment hedge forward points amortization	(7.0)	(1.5)	0.0
Gains (losses) on net investment hedges	21.6	3.5	0.0
Unrealized gains (losses) on pension benefit obligation, net of tax	(1.5)	5.5	(4.1)
Currency translation adjustment	103.8	(67.8)	158.7
Total other comprehensive income (loss), net of tax	105.2	76.5	1.5
Comprehensive income attributable to Biogen Inc.	5,993.7	4,507.2	2,540.6
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	0.4	(42.9)	(131.0)
Comprehensive income	$ 5,993.3	$ 4,550.1	$ 2,671.6

Collaborative and Other Relationships Collaborative and Other Relationships - Eisai (Details 1) - Eisai - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of future development costs related to Eisai	15.00%	45.00%
BAN2401 and Elenbecestat R&D expense incurred by collaboration		$ 348.7	$ 232.0	$ 146.2
Biogen's share of expense reflected within our consolidation statements of income		174.3	116.0	74.3
Research and development \| Aducanumab
Collaborative arrangements and non-collaborative arrangement transactions
Aducanumab expense incurred by the collaboration		179.4	264.8	268.7
Biogen's share of expense reflected within our consolidation statements of income		98.7	234.6	268.7
Selling, General and Administrative Expenses \| Aducanumab
Collaborative arrangements and non-collaborative arrangement transactions
Aducanumab expense incurred by the collaboration		27.4	50.6	23.6
Biogen's share of expense reflected within our consolidation statements of income		$ 15.1	$ 27.3	$ 23.6

Consolidated Statements of Equity - USD ($) $ in Millions	Total	Preferred stock	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Retained earnings	Treasury stock	Noncontrolling interests	Parent	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	2018 Share Repurchase Program	2018 Share Repurchase Program Common stock	2018 Share Repurchase Program Additional paid-in capital	2018 Share Repurchase Program Retained earnings	2018 Share Repurchase Program Treasury stock	2016 Share Repurchase Program	2016 Share Repurchase Program Common stock	2016 Share Repurchase Program Additional paid-in capital	2016 Share Repurchase Program Retained earnings	2016 Share Repurchase Program Treasury stock	2011 Share Repurchase Program	2011 Share Repurchase Program Treasury stock
Beginning Balance at Dec. 31, 2016	$ 12,128.6	$ 0.0	$ 0.1	$ 0.0	$ (319.9)	$ 15,071.6	$ 2,611.7
Beginning Balance at Dec. 31, 2016	12,140.1
Beginning Balance at Dec. 31, 2016								$ (11.5)
Beginning Balance, shares at Dec. 31, 2016		0	(238,500,000)				(22,600,000)
Net income attributable to Biogen Inc.	2,539.1					2,539.1
Net income (loss) attributable to noncontrolling interests, net of tax	131.0							131.0
Net income	2,670.1
Other comprehensive income (loss), net of tax	1.5				1.5
Other comprehensive income (loss), net of tax	1.5							0.0
Capital contribution by noncontrolling interest	15.8							15.8	$ 0.0
Distribution to noncontrolling interests	(150.0)							(150.0)	0.0
Repurchase of common stock, at cost																				$ (1,000.0)				$ (1,000.0)	$ (365.4)	$ (365.4)
Repurchase of common stock, at cost, shares																				(3,700,000)				(3,700,000)		(1,200,000)
Retirement of common stock pursuant to the 2018 Share Repurchase Program, at cost																				$ 0.0	$ 0.0	$ 36.0	$ 964.0	$ 1,000.0
Retirement of common stock pursuant to the 2016 Share Repurchase Program, at cost, shares																					3,700,000			3,700,000
Issuance of common stock under stock option and stock purchase plans, shares			200,000
Issuance of common stock under stock options and stock purchase plans, value	40.5		$ 0.0	40.5
Issuance of common stock under stock award plan, shares			300,000
Issuance of common stock under stock award plan	(45.8)		$ 0.0	(44.8)		(1.0)
Hemophilia spin-off adjustment	(852.8)
Tax benefit	(17.5)					17.5			(17.5)
Ending Balance at Dec. 31, 2017	12,598.1	$ 0.0	$ 0.1	97.8	(318.4)	15,810.4	$ (2,977.1)
Ending Balance at Dec. 31, 2017	12,612.8
Ending Balance at Dec. 31, 2017								(14.7)
Ending Balance, shares at Dec. 31, 2017		0	(235,300,000)				(23,800,000)
Net income attributable to Biogen Inc.	4,430.7					4,430.7
Net income (loss) attributable to noncontrolling interests, net of tax	43.3							43.3
Net income	4,474.0
Other comprehensive income (loss), net of tax	76.5				76.5
Other comprehensive income (loss), net of tax	(76.1)							(0.4)
Capital contribution by noncontrolling interest	13.8							13.8	0.0
Distribution to noncontrolling interests	(50.0)							(50.0)	0.0
Repurchase of common stock, at cost	(3,000.0)														$ (1,352.6)				$ (1,352.6)	$ (3,000.0)				$ (3,000.0)
Repurchase of common stock, at cost, shares															(4,300,000)				(4,300,000)	(10,500,000)				(10,500,000)
Retirement of common stock pursuant to the 2018 Share Repurchase Program, at cost															$ 0.0	$ 0.0	$ 92.8	$ 1,259.8	$ 1,352.6	$ 0.0	$ 0.0	$ 171.1	$ 2,828.9	$ 3,000.0
Retirement of common stock pursuant to the 2016 Share Repurchase Program, at cost, shares																4,300,000			4,300,000		10,500,000			10,500,000
Issuance of common stock under stock option and stock purchase plans, shares			200,000
Issuance of common stock under stock options and stock purchase plans, value	41.2		$ 0.0	41.2
Issuance of common stock under stock award plan, shares			300,000
Issuance of common stock under stock award plan	(43.8)		$ 0.0	(43.8)
Compensation related to share-based payments	(168.7)			(168.7)
Adoption of new accounting guidance	106.1				1.5	104.6
Ending Balance at Dec. 31, 2018	13,031.6	$ 0.0	$ 0.1	0.0	(240.4)	16,257.0	$ (2,977.1)
Ending Balance at Dec. 31, 2018	13,039.6
Ending Balance at Dec. 31, 2018	(8.0)							(8.0)
Ending Balance, shares at Dec. 31, 2018		0	(221,000,000.0)				(23,800,000)
Net income attributable to Biogen Inc.	5,888.5					5,888.5
Net income (loss) attributable to noncontrolling interests, net of tax	0.0							0.0
Net income	5,888.5
Other comprehensive income (loss), net of tax	105.2				105.2
Other comprehensive income (loss), net of tax	104.8							(0.4)
Capital contribution by noncontrolling interest	4.3							4.3	$ 0.0
Repurchase of common stock, at cost										$ (3,720.9)				$ (3,720.9)	$ (2,147.4)				$ (2,147.4)
Repurchase of common stock, at cost, shares										(14,700,000)				(14,700,000)	(8,900,000)				(8,900,000)
Retirement of common stock pursuant to the 2018 Share Repurchase Program, at cost										$ 0.0	$ 0.0	$ 121.5	$ 3,599.4	$ 3,720.9	$ 0.0	$ 0.0	$ 110.5	$ 2,036.9	$ 2,147.4
Retirement of common stock pursuant to the 2016 Share Repurchase Program, at cost, shares											14,700,000			14,700,000		8,900,000			8,900,000
Issuance of common stock under stock option and stock purchase plans, shares			200,000
Issuance of common stock under stock options and stock purchase plans, value	$ 40.8		$ 0.0	40.8		0.0
Issuance of common stock under stock award plan, shares	15,000		400,000
Issuance of common stock under stock award plan	$ (53.8)		$ 0.0	0.0		53.8
Compensation related to share-based payments	(191.2)			(191.2)
Ending Balance at Dec. 31, 2019	13,339.1	$ 0.0	$ 0.1	$ 0.0	$ (135.2)	$ 16,455.4	$ (2,977.1)
Ending Balance at Dec. 31, 2019	13,343.2
Ending Balance at Dec. 31, 2019	$ (4.1)							$ (4.1)
Ending Balance, shares at Dec. 31, 2019		0	(198,000,000.0)				(23,800,000)

Inventory (Tables)

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Components of inventory

The components of inventory are summarized as follows:



	As of December 31,
(In millions)	2019		2018
Raw materials	$	169.7	$	196.3
Work in process	460.0		606.7
Finished goods	174.5		133.5
Total inventory	$	804.2	$	936.5

Balance Sheet Classification:
Inventory	$	804.2	$	929.9
Investments and other assets	—		6.6
Total inventory	$	804.2	$	936.5

Collaborative and Other Relationships

12 Months Ended

Dec. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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; and 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.

Our collaboration arrangements will continue in effect until we mutually agree to terminate the collaboration, except that 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 any other anti-CD20 products in development in exchange for a royalty and our rights to GAZYVA in exchange for the compensation described in the table 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. We recognize our share of the development and commercialization expenses of GAZYVA as a reduction of our share of pre-tax profits in revenues from anti-CD20 therapeutic programs.

Commercialization of GAZYVA impacts our percentage of the co-promotion profits for RITUXAN, as summarized in the table below.

OCREVUS

In March 2017 the FDA approved OCREVUS for the treatment of RMS and PPMS. 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% if annual net sales exceed $900.0 million. There will be a 50% reduction to these royalties if a biosimilar to OCREVUS is approved in the U.S.

In addition, we receive a gross 3% 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. OCREVUS has been approved for the treatment of RMS and PPMS in the E.U. and certain other countries.

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 revenues were 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 revenues will be adjusted for in the period in which they become known, which is expected to be the following quarter.

Profit-sharing Formulas

RITUXAN Profit Share

Our current pretax co-promotion profit-sharing formula for RITUXAN provides for a 30% share on the first $50.0 million of co-promotion operating profits earned each calendar year. Our share of annual co-promotion profits in excess of $50.0 million varies, as summarized in the table below, upon the following events:



Until GAZYVA First Non-CLL FDA Approval	40.0	%
After GAZYVA First Non-CLL FDA Approval until First GAZYVA Threshold Date	39.0	%
After First GAZYVA Threshold Date until Second GAZYVA Threshold Date	37.5	%
After Second GAZYVA Threshold Date	35.0	%

First Non-CLL GAZYVA FDA Approval means the FDA’s first approval of GAZYVA in an indication other than CLL.

Our share of RITUXAN pre-tax profits in the U.S. decreased from 39% to 37.5% in the third quarter of 2017 as gross sales of GAZYVA in the U.S. for the preceding 12-month period exceeded $150.0 million.

In addition, should the FDA approve an anti-CD20 product other than OCREVUS or GAZYVA that is acquired or developed by Genentech and subject to the collaboration agreement, our share of the co-promotion operating profits would be between 30% and 37.5% based on certain events.

GAZYVA Profit Share

Our current pretax profit-sharing formula for GAZYVA provides for a 35% share on the first $50.0 million of operating profits earned each calendar year. Our share of annual profits in excess of $50.0 million varies, as summarized in the table below, upon the following events:



Until First GAZYVA Threshold Date	39.0	%
After First GAZYVA Threshold Date until Second GAZYVA Threshold Date	37.5	%
After Second GAZYVA Threshold Date	35.0	%

Our share of GAZYVA operating profits in 2019 and 2018 was 37.5%. In 2017 our share of operating profits on GAZYVA was 35%.

In November 2017 the FDA approved GAZYVA in combination with chemotherapy, followed by GAZYVA alone, for people with previously untreated advanced follicular lymphoma.

Revenues from Anti-CD20 Therapeutic Programs

Revenues from anti-CD20 therapeutic programs are summarized as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses	$	1,542.4	$	1,431.9	$	1,316.4
Other revenues from anti-CD20 therapeutic programs	748.0		548.3		242.8
Total revenues from anti-CD20 therapeutic programs	$	2,290.4	$	1,980.2	$	1,559.2

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

Ionis Pharmaceuticals, Inc.

SPINRAZA

In January 2012 we entered into a collaboration and license agreement with Ionis pursuant to which we have an exclusive, worldwide license to develop and commercialize SPINRAZA for the treatment of SMA. SPINRAZA was approved for the treatment of SMA in the U.S., E.U. and Japan in December 2016, June 2017 and July 2017, respectively.

For the years ended December 31, 2019, 2018 and 2017, we recognized product revenues of $2,097.0 million, $1,724.2 million and $883.7 million, respectively, on our sales of SPINRAZA. 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% and 15%, 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, 2019, 2018 and 2017, totaled $293.0 million, $238.0 million and $112.4 million, respectively.

During 2017 we made milestone payments to Ionis totaling $150.0 million related to the marketing approvals discussed above, which were capitalized in intangible assets, net in our consolidated balance sheets.

Antisense Therapeutics

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 candidatethrough 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 candidateuntil 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 salesif we successfully develop the product candidate after option exercise.

Upon entering into this agreement, we made an upfront payment of $30.0 million to Ionis and agreed to make potential additional payments, prior to licensing, of up to $10.0 million based on the development of the selected product candidate as well as a mark-up of the cost estimate of the Phase 1 and Phase 2 trials. During 2015 we recognized this $10.0 million developmental milestone upon the selection of BIIB080 (tau ASO), which is currently in Phase 1 development for the potential treatment of AD.

In December 2019 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize BIIB080. 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 of in the low- to mid-teens if we successfully develop the product candidate after option exercise.

2018 Ionis Agreement

In June 2018 we closed a 10-year exclusive collaboration agreement with Ionis to develop novel antisense oligonucleotide (ASO) drug candidates for a broad range of neurological diseases (2018 Ionis Agreement) 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.

The 11.5 million shares of Ionis common stock were purchased at a premium to their fair value at the transaction closing date. The premium consisted of acquiring the shares at a price above the fair value based on the trailing 10-day weighted-average close price prior to entering into the 2018 Ionis Agreement in April 2018 and the effect of certain holding period restrictions. We recorded an asset of $462.9 million in investments and other assets in our consolidated balance sheets reflecting the fair value of the common stock as of the purchase date and a charge of $162.1 million to research and development expense in our consolidated statements of income in the second quarter of 2018 reflecting the premium paid for the common stock.

Our investment in Ionis common stock is remeasured each reporting period. Changes in the fair value of our investment in Ionis common stock, including the effect of the holding period restrictions, are reflected in other income (expense), net in our consolidated statements of income. For additional information on the fair value of our investment in Ionis common stock, please read Note 7, Fair Value Measurements, to these consolidated financial statements.

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 year ended December 31, 2019, we incurred milestones of $30.0 million related to the advancement of neurological targets identified under this agreement.

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.

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 BIIB067 (tofersen), an investigational treatment for ALS with superoxide dismutase 1 (SOD1) mutations. In connection with the option exercise, we made a payment of $35.0 million to Ionis, which was recorded as research and development in our consolidated statements of income. Future payments may include potential post-licensing milestone payments of 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 expenses related to the development, manufacturing and commercialization of tofersen following the option exercise.

During the years ending December 31, 2019, 2018 and 2017, we incurred milestones of $20.0 million, $18.0 million and $12.0 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.

Eisai Co., Ltd.

BAN2401 and Elenbecestat Collaboration

We have a collaboration agreement with Eisai Co., Ltd. (Eisai) to jointly develop and commercialize BAN2401, a monoclonal antibody that targets amyloid beta aggregates for the potential treatment of AD, and elenbecestat, the oral BACE (base amyloid cleaving enzyme) inhibitor (the BAN2401 and Elenbecestat Collaboration).

In September 2019 we and Eisai announced the decision to discontinue the global Phase 3 studies (MISSION AD1 and MISSION AD2) of elenbecestat in early AD. As a result of this decision, in the third quarter of 2019, we accrued approximately $48.0 million related to our share of the termination of various clinical trials and research and development contracts incurred under the BAN2401 and Elenbecestat Collaboration.

Eisai serves as the global operational and regulatory lead for BAN2401 and all costs, including research, development, sales and marketing expenses, are shared equally between us and Eisai. Upon marketing approval we and Eisai will co-promote BAN2401 and share profits equally. In addition, the BAN2401 and Elenbecestat Collaboration provides both parties with certain rights and obligations in the event of a change in control of either party.

The BAN2401 and Elenbecestat Collaboration also provided Eisai with an option to jointly develop and commercialize aducanumab, our anti-amyloid beta antibody candidate for early AD (Aducanumab 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 Aducanumab Option and we entered into a new collaboration agreement for the joint development and commercialization of aducanumab (Aducanumab Collaboration Agreement). Eisai has not yet exercised its Anti-Tau Option.

Under the Aducanumab Collaboration Agreement, the two companies will continue to jointly develop BAN2401 in accordance with the BAN2401 and Elenbecestat Collaboration; however, we are no longer required to pay Eisai any milestone payments for products containing BAN2401 and we are no longer entitled to any potential development and commercial milestone payments from Eisai in relation to aducanumab.

A summary of development and sales and marketing expenses related to the BAN2401 and Elenbecestat Collaboration is as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Total development expense incurred by the collaboration related to the advancement of BAN2401 and Elenbecestat	$	348.7	$	232.0	$	146.2
Biogen's share of BAN2401 and Elenbecestat development expense reflected in research and development expense in our consolidated statements of income	$	174.3	$	116.0	$	74.3

Total sales and marketing expense incurred by the collaboration	$	32.4	$	10.7	$	—
Biogen's share of BAN2401 and Elenbecestat sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	$	16.2	$	5.4	$	—

Aducanumab Collaboration Agreement

Under the Aducanumab Collaboration Agreement, the two companies will co-promote aducanumab with a region-based profit split and we lead the ongoing development of aducanumab.

In March 2019, based on a pre-specified futility analysis, we discontinued the global Phase 3 trials, EMERGE and ENGAGE, designed to evaluate the efficacy and safety of aducanumab in patients with early AD. A new analysis of a larger dataset from these trials, conducted in consultation with the FDA, showed that the Phase 3 EMERGE

study met its pre-specified primary and secondary endpoints. In October 2019 we and Eisai announced that we plan to pursue regulatory approval for aducanumab in the U.S.

For the period through March 31, 2018, we were responsible for 100% of development costs incurred by the collaboration for the advancement of aducanumab (aducanumab development expense). For the period April 1, 2018 through December 31, 2018, Eisai reimbursed us for 15% of aducanumab development expense incurred and beginning January 1, 2019, is reimbursing us for 45% of aducanumab development expense incurred.

In the first quarter of 2019, as a result of the decision to discontinue the Phase 3 EMERGE and ENGAGE trials following the futility analysis, we accrued and subsequently paid approximately $45.0 million related to the termination of various clinical trials and research and development contracts net of the expected 45% Eisai reimbursement of development costs incurred under the Aducanumab Collaboration Agreement.

Upon commercialization, both companies will co-promote aducanumab with a region-based profit split. We will receive a 55% share of the potential profits (losses) in the U.S., a 68.5% share of the potential profits (losses) in the E.U. and a 20% share of the potential profits (losses) in Japan and Asia, excluding China and South Korea. The two companies will continue to share equally in the potential profits (losses) in rest of world markets. Sales and marketing expense incurred before commercialization are shared in proportion to the same region-based profit split that will be utilized to co-promote aducanumab.

A summary of development and sales and marketing expenses related to the Aducanumab Collaboration Agreement is as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Total aducanumab development expense	$	179.4	$	264.8	$	268.7
Biogen's share of aducanumab development expense reflected in research and development expense in our consolidated statements of income	$	98.7	$	234.6	$	268.7

Total aducanumab sales and marketing expense incurred by the collaboration	$	27.4	$	50.6	$	23.6
Biogen's share of aducanumab sales and marketing expense reflected in selling, general and administrative expense in our consolidated statements of income	$	15.1	$	27.3	$	23.6

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.

Anti-Tau Option

Eisai may exercise the Anti-Tau Option after completion of the Phase 1 clinical trial of such anti-tau monoclonal antibody. If Eisai exercises its Anti-Tau Option, we will receive an upfront payment from Eisai and will be entitled to additional development and commercial milestone payments.

Alkermes

In November 2017 we entered into an exclusive license and collaboration agreement with 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. In November 2019 VUMERITY became available in the U.S.

Under this agreement, we received an exclusive, worldwide license to develop and commercialize VUMERITY and we pay Alkermes a royalty of 15% on worldwide net commercial sales of VUMERITY. 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.

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.

Upon entering into this agreement, we made a $28.0 million upfront payment to Alkermes representing our share of VUMERITY development costs already incurred in 2017. Beginning in 2018 we became responsible for all

development expenses related to VUMERITY. In December 2017 we also recognized a $50.0 million expense, which was paid to Alkermes in 2018, enabling the continuation of the agreement to develop VUMERITY. Both the $28.0 million upfront payment and $50.0 million continuation payment were recorded as research and development expense in our consolidated financial statements during the year ended December 31, 2017.

During the fourth quarter of 2019, following the FDA's approval of VUMERITY, we paid Alkermes $155.0 million in milestone payments, which were recorded in intangible assets in our consolidated balance sheets and will be amortized over the useful life of the product. For the years ended December 31, 2019, 2018 and 2017, we recorded $53.5 million, $68.7 million and $80.3 million, respectively, in research and development expense in our consolidated statements of income related to this collaboration.

Alkermes currently supplies VUMERITY to us pursuant to a supply agreement with Alkermes. In October 2019 we entered into a new supply agreement and amended our license and collaboration agreement with Alkermes pursuant to which we have the election, following a transition period, to manufacture VUMERITY or have manufacturing transitioned to a third party in exchange for an increase in the royalty rate on worldwide net commercial sales of VUMERITY that is manufactured by us or our designee.

Bristol-Myers Squibb Company

In June 2017 we completed an exclusive license agreement with Bristol-Myers Squibb Company (BMS) for the development and potential commercialization of BIIB092 (gosuranemab), an antibody targeting tau, the protein that forms the deposits, or tangles, in the brain associated with AD.

Under this agreement, we received worldwide rights to gosuranemab and are responsible for the full development and potential commercialization of gosuranemab in AD and progressive supranuclear palsy (PSP).

In December 2019 we announced that the Phase 2 PASSPORT study investigating gosuranemab in individuals with PSP did not meet its primary endpoint. Based on these results, we discontinued development of gosuranemab in PSP and other primary tauopathies. We will continue our ongoing Phase 2 TANGO study of gosuranemab for mild cognitive impairment due to AD or mild AD, given differences in disease pathology.

Upon entering into this agreement, we made an upfront payment of $300.0 million to BMS and assumed all remaining obligations to the former shareholders of iPierian, Inc. (iPierian) related to BMS’s acquisition of iPierian in 2014. In June 2017 we recognized a $60.0 million developmental milestone payable to the former shareholders of iPierian upon dosing of the first patient in the Phase 2 PASSPORT study of gosuranemab for PSP. Both the $300.0 million upfront payment and the $60.0 million developmental milestone payment were recorded as research and development expense in our consolidated statements of income for the year ended December 31, 2017.

We may pay BMS up to $360.0 million in additional milestone payments, and potential royalties, and we may pay the former shareholders of iPierian up to $370.0 million in remaining milestone payments as well as potential royalties on net commercial sales.

For the years ended December 31, 2019 and 2018, we recorded $144.0 million and $97.0 million, respectively, in research and development expense in our consolidated statements of income related to this collaboration.

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. The next expected milestone would be $15.0 million, due if ex-U.S. net sales reach $100.0 million over a period of four consecutive quarters. Royalty payments are recognized in cost of sales within our consolidated statements of income.

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 is 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.

For the years ending December 31, 2019, 2018 and 2017, total cost of sales related to royalties and commercial supply of FAMPYRA reflected in our consolidated statements of income were $42.0 million, $36.5 million and $34.0 million, respectively.

AbbVie Inc.

We have a collaboration agreement with AbbVie for the development and commercialization of ZINBRYTA, which was approved for the treatment of RMS in the U.S. in May 2016 and in the E.U. in July 2016. The collaboration began selling ZINBRYTA in the third quarter of 2016. In March 2018 we and AbbVie announced the voluntary worldwide withdrawal of ZINBRYTA for RMS.

Under this agreement, we and AbbVie conducted ZINBRYTA co-promotion activities in the U.S., E.U. and Canadian territories, where development and commercialization costs and profits were shared equally.

We were responsible for manufacturing and research and development activities and recorded these activities within their respective lines in our consolidated statements of income, net of any reimbursement of research and development expenditures received from AbbVie. For the years ended December 31, 2019, 2018 and 2017, the collaboration incurred $0.6 million, $32.4 million and $39.9 million for research and development activities, respectively, for which we recognized $0.3 million, $16.2 million and $19.9 million, respectively, in our consolidated statements of income.

Co-promotion Profits and Losses

In the U.S., AbbVie recognized revenues on sales to third parties and we recognized our 50% share of the co-promotion profits or losses as a component of total revenues in our consolidated statements of income.

Our share of the co-promotion losses on ZINBRYTA in the U.S. for the year ended December 31, 2019, was immaterial. For the years ended December 31, 2018 and 2017, we recognized a net reduction in revenues from collaborative and other relationships, a component of other revenues, of $8.6 million and $16.9 million, respectively, to reflect our share of the overall net losses within the collaboration for each of those years.

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.

Skyhawk Therapeutics, Inc.

In January 2019 we entered into a collaboration and research and development services agreement with Skyhawk Therapeutics, Inc. (Skyhawk) pursuant to which the companies are leveraging Skyhawk's SkySTAR technology platform with the goal of discovering innovative small molecule treatments for patients with neurological diseases, including MS and SMA. We are responsible for the development and potential commercialization of any therapies resulting from this collaboration and we may also pay Skyhawk up to a total of approximately $2.4 billion in additional milestone payments as well as potential royalties on net commercial sales.

In connection with this agreement, we made an upfront payment of $74.0 million to Skyhawk, of which $38.5 million was recorded as research and development expense in our consolidated statements of income and $35.5 million was recorded as prepaid research and development expenditures within investments and other assets in our consolidated balance sheets and will be expensed as the services are provided. In October 2019 we amended this agreement to add an additional discovery program. In connection with this amendment, we made a payment to Skyhawk of $15.0 million, of which approximately $8.0 million was recorded as research and development and approximately $7.0 million was recorded as prepaid research and development expenditures within investments and other assets in our consolidated balance sheets.

Other

For the years ended December 31, 2019, 2018 and 2017, we entered into several research, discovery and other related arrangements that resulted in $30.6 million, $22.0 million and $10.0 million, respectively, recorded as research and development expense in our consolidated statements of income.

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% stake in Samsung Bioepis and we contributed 49.5 billion South Korean won (approximately $45.0 million) for the remaining 15% 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%, which reflected the effect of previous equity financings in which we did not participate, to approximately 49.9%. The share purchase transaction was completed in November 2018 and, upon closing, we paid 759.5 billion South Korean won ($676.6 million) to Samsung BioLogics. As of December 31, 2019, our ownership percentage remained at approximately 49.9%.

We recognize 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 become available, which is reflected as equity in income (loss) of investee, net of tax in our consolidated statements of income. During 2015, as our share of losses exceeded the carrying value of our initial investment, we suspended recognizing additional losses. In the first quarter of 2019 we restarted recognizing our share of Samsung Bioepis' income (losses), and we began recognizing amortization on certain basis differences resulting from our November 2018 investment.

Upon investment, the equity method of accounting requires 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 are amortized over their economic life. The total basis difference was approximately $675 million, consisting of approximately $115 million attributed to inventory, approximately $615 million attributed to developed technology and approximately $170 million attributed to IPR&D. A deferred tax liability of $225 million was established for the acquired assets that had no tax basis. The basis differences related to inventory and developed technology will be amortized, net of tax, over their estimated useful lives of 1.5 years and 15 years, respectively, one quarter in arrears.

Our joint venture partner, Samsung BioLogics, is currently subject to an ongoing criminal investigation that we continue to monitor. While this investigation could impact the operations of Samsung Bioepis and its business, we have assessed the value of our investment in Samsung Bioepis and continue to believe that the fair value of the investment is in excess of its net book value.

For the year ended December 31, 2019, we recognized losses on our investment of $79.4 million. These losses reflect our share of losses totaling $1.2 million and amortization of basis differences totaling $78.2 million.

2019 Transaction

In December 2019 we completed a transaction with Samsung Bioepis and secured the exclusive rights to commercialize two potential ophthalmology biosimilar products, SB11 referencing LUCENTIS and SB15 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.

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 and $37.0 million was recorded as an intangible asset in our consolidated balance sheets. Additionally, we may pay Samsung Bioepis up to $210.0 million in additional development, regulatory and sales-based milestones, including a $15.0 million development milestone that we may pay in 2020.

We also acquired an option to extend the term of our current European 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 exclusive rights to commercialize these products in China.

2013 Commercial Agreement

In December 2013 pursuant to our rights under the joint venture agreement with Samsung BioLogics, 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.

In April 2018 we and Samsung Bioepis announced an agreement with AbbVie related to the commercialization of IMRALDI. Under the terms of the agreement, AbbVie granted us and Samsung Bioepis patent licenses for the use and sale of IMRALDI in Europe, on a country-by-country basis, and we make royalty payments to AbbVie on behalf of Samsung Bioepis. We began to recognize revenues on sales of IMRALDI to third parties in Europe in the fourth quarter of 2018.

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

We share 50% 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, 2019, 2018 and 2017, we recognized a net profit-sharing expense of $241.6 million, $187.4 million and $111.0 million, respectively, to reflect Samsung Bioepis' 50% sharing of the net collaboration profits.

Other Services

Simultaneous with the formation of Samsung Bioepis, we also entered into a technical development services agreement, a manufacturing agreement and a license agreement with Samsung Bioepis.

Under the technical development services agreement, we provide Samsung Bioepis technical development and technology transfer services, which include, but are not limited to, cell culture development, purification process development, formulation development and analytical development.

Under the manufacturing agreement, we manufacture clinical and commercial quantities of bulk drug substance of biosimilar products for Samsung Bioepis pursuant to contractual terms.

Following the divestiture of our Hillerød, Denmark manufacturing operations in August 2019 FUJIFILM assumed responsibility for the manufacture of clinical and commercial quantities of bulk drug substance of biosimilar products for Samsung Bioepis. We no longer recognize revenues for the manufacturing completed after the divestiture date under the technical development services and manufacturing agreements with Samsung Bioepis. For additional information on the divestiture of our Hillerød, Denmark manufacturing operations, please read Note 3, Divestitures, to these consolidated financial statements.

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 all biosimilar products developed and commercialized by Samsung Bioepis.

For the years ended December 31, 2019, 2018 and 2017, we recognized $106.2 million, $96.4 million and $42.7 million, respectively, in revenues under the license, technical development services and manufacturing agreements, which is reflected in revenues from collaborative and other relationships, as a component of other revenues in our consolidated statements of income.

Amounts receivable from Samsung Bioepis related to the agreements discussed above were $85.0 million and $116.9 million as of December 31, 2019 and 2018, respectively. Amounts payable to Samsung Bioepis as of December 31, 2019, consisted of the $100.0 million upfront payment related to the 2019 transaction we completed in December 31, 2019, as discussed above. Amounts payable to Samsung Bioepis as of December 31, 2018, were $31.5 million.

Subsequent Events Subsequent Events	12 Months Ended
Subsequent Events Subsequent Events	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Pfizer Inc. In January 2020 we entered into an agreement to acquire PF-05251749, a novel CNS-penetrant small molecule inhibitor of casein kinase 1, for the potential treatment of patients with behavioral and neurological symptoms across various psychiatric and neurological diseases from Pfizer. In particular, we plan to develop the Phase 1 asset for the treatment of sundowning in AD and irregular sleep wake rhythm disorder in Parkinson’s disease. In connection with the closing of this transaction, we will make an upfront payment of $75.0 million to Pfizer, which will be recorded as acquired IPR&D in our consolidated statements of income as PF-05251749 has not yet reached technological feasibility. We may also pay Pfizer up to $635.0 million in potential additional development and commercialization milestone payments, as well as tiered royalties in the high single digits to sub-teens. This transaction will be accounted for as an asset acquisition and is subject to customary closing conditions, including the expiration of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 in the U.S. We expect the transaction to close in the first quarter of 2020. 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 entered into in August 2015.

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

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)	2019			2018
Land	$	118.1		$	144.5
Buildings	835.0			1,282.8
Leasehold improvements	99.5			94.4
Machinery and equipment	844.5			1,258.1
Computer software and hardware	798.4			798.7
Furniture and fixtures	58.3			61.6
Construction in progress	2,084.4			1,758.5
Total cost	4,838.2			5,398.6
Less: accumulated depreciation	(1,590.9		)	(1,797.4		)
Total property, plant and equipment, net	$	3,247.3		$	3,601.2

Depreciation expense totaled $190.6 million, $269.4 million and $266.3 million for 2019, 2018 and 2017, respectively.

For 2019, 2018 and 2017 we capitalized interest costs related to construction in progress totaling approximately $68.8 million, $54.0 million and $30.7 million, respectively. The increase in capitalized interest costs is primarily due to the construction of our large-scale biologics manufacturing facility in Solothurn, Switzerland, as discussed below.

Solothurn, Switzerland Manufacturing Facility

In order to support our drug development pipeline, we are building a large-scale biologics manufacturing facility in Solothurn, Switzerland. We expect this facility to be partially operational by the end of 2020. Upon completion, the 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, 2019 and 2018, we had approximately $1.9 billion and $1.6 billion, respectively, capitalized as construction in progress related to this facility.

Divestiture of Hillerød, Denmark Manufacturing Operations

In August 2019 we completed the sale of all of the outstanding shares of our subsidiary that owned our biologics manufacturing operations in Hillerød, Denmark to FUJIFILM. This transaction included $631.5 million of property, plant and equipment, which was primarily comprised of $312.5 million for buildings and $287.3 million for machinery and equipment. For additional information on the divestiture of our Hillerød, Denmark manufacturing operations, please read Note 3, Divestitures, to these consolidated financial statements.

Investments in Variable Interest Entities	12 Months Ended
Investments in Variable Interest Entities	Dec. 31, 2019
Investments in Variable Interest Entities [Abstract]
Investments in Variable Interest Entities	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 SubOne AG (Neurimmune) for the development and commercialization of antibodies for the potential treatment of AD, including aducanumab, our anti-amyloid beta antibody candidate for the potential treatment of AD (as amended, the Neurimmune Agreement). We are responsible for the development, manufacturing and commercialization of all licensed products. This 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 any product using such a licensed compound. 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% of the research and development costs incurred in support of the collaboration. In October 2017 we amended the terms of the Neurimmune Agreement and made a $150.0 million payment to Neurimmune in exchange for a 15% reduction in the previously negotiated royalty rates payable on products developed under the Neurimmune Agreement, including royalties payable on potential commercial sales of aducanumab. In May 2018 we made an additional $50.0 million payment to Neurimmune to further reduce the previously negotiated royalty rates payable on products developed under the Neurimmune Agreement, including royalties payable on potential commercial sales of aducanumab, by an additional 5%. Our royalty rates payable on products developed under the Neurimmune Agreement, including royalty rates payable on potential commercial sales of aducanumab, now range from the high single digits to sub-teens. As we consolidate the results of Neurimmune, we treated these payments as distributions and recognized them as charges to noncontrolling interests in the fourth quarter of 2017 and the second quarter of 2018, as applicable. Additionally, under the terms of the Neurimmune Agreement, we would be required to pay Neurimmune a milestone payment of $75.0 million upon the regulatory filing with the FDA for approval of aducanumab and a milestone payment of $100.0 million if aducanumab is launched in the U.S. 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, 2019, 2018 and 2017, amounts reimbursed were immaterial. 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 previously contractually required amounts. Under the Aducanumab Collaboration Agreement, Eisai had an option to share in the benefit and cost associated with the royalty reductions discussed above; however, Eisai did not elect to share in the benefit and cost with respect to either the October 2017 or May 2018 royalty reductions, which will impact the amount of profits (losses) on potential commercial sales of aducanumab to be shared with Eisai. For additional information on our collaboration arrangements with Eisai, please read Note 18, 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, 2019 and 2018, the carrying value of our investments in certain biotechnology companies representing potential unconsolidated variable interest entities totaled $22.7 million and $28.7 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 previously contractually required amounts.

Derivative Instruments

12 Months Ended

Dec. 31, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments

Foreign Currency Forward Contracts - Hedging Instruments

Due to the global nature of our operations, portions of our revenues and operating expenses are recorded in currencies other than the U.S. dollar. The value of revenues and operating expenses measured in U.S. dollars is therefore subject to changes in foreign currency exchange rates. In order to mitigate these changes, we use foreign currency forward contracts to lock in exchange rates associated with a portion of our forecasted international revenues and operating expenses.

Foreign currency forward contracts in effect as of December 31, 2019 and 2018, had durations of 1 to 15 months and 1 to 12 months, respectively. These contracts have been designated as cash flow hedges and unrealized gains or losses on the portion of these foreign currency forward contracts that are included in the effectiveness test are reported in accumulated other comprehensive income (loss) (referred to as AOCI in the tables below). Realized gains and losses of such contracts are recognized in revenues when the sale of product in the currency being hedged is recognized and in operating expenses when the expense in the currency being hedged is recorded. We recognize all cash flow hedge reclassifications from accumulated other comprehensive income and fair value changes of excluded portions in the same line item in our consolidated statements of income that has been impacted by the hedged item.

The notional value of foreign currency forward contracts that were entered into to hedge forecasted revenues and operating expenses is summarized as follows:



	Notional Amount As of December 31,
Foreign Currency: (In millions)	2019		2018
Euro	$	1,892.4	$	1,701.4
British pound sterling	—		215.3
Swiss francs	—		131.4
Japanese yen	—		98.8
Canadian dollar	—		92.2
Total foreign currency forward contracts	$	1,892.4	$	2,239.1

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 $0.5 million as of December 31, 2019, net gains of $27.3 million as of December 31, 2018, and net losses of $113.0 million as of December 31, 2017. We expect the net gains of $0.5 million to be settled over the next 15 months, of which $2.4 million of these gains are expected to be settled over the next 12 months, with any amounts in accumulated other comprehensive income (loss) to be reported as an adjustment to revenues or operating expenses. 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, 2019 and 2018, credit risk did not change the fair value of our foreign currency forward contracts.

The following tables summarize 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	2019			2018			Location	2019		2018
Revenues	$	118.6		$	(42.5	)	Revenues	$	2.9	$	10.8
Operating expenses	$	(3.3	)	$	0.2		Operating expenses	$	0.2	$	(0.1	)



For the Years Ended December 31,
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)				Net Gains/(Losses) Recognized Directly into Net Income (in millions)
Location	2017			Location	2017
Revenues	$	(32.5	)	Other income (expense)	$	8.9
Operating expenses	$	0.6		Other income (expense)	$	(0.2	)

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, as described in Note 12, Indebtedness, to these consolidated financial statements, we entered into interest rate swaps with an aggregate notional amount of $675.0 million, which expire on September 15, 2020. The interest rate swap contracts are designated as hedges of the fair value changes in our 2.90% Senior Notes attributable to changes in interest rates. The carrying value of our 2.90% Senior Notes as of December 31, 2019 and 2018, includes approximately $2.3 million and $14.5 million, respectively, related to changes in the fair value of these interest rate swap contracts. Since the specific terms and notional amount of the swaps match the debt being hedged, it is assumed to be a highly effective hedge and all changes in the fair value of the swaps are recorded as a component of our 2.90% Senior Notes with no net impact recorded in income. Any net interest payments made or received on the interest rate swap contracts are recorded as a component of interest expense in our consolidated statements of income.

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% 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 is 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 have entered into foreign currency forward contracts. Foreign currency forward contracts in effect as of December 31, 2019, had remaining durations of 10 months. These contracts have been designated as net investment hedges. We recognize changes in the spot exchange rate 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 losses of $1.5 million and $3.8 million as of December 31, 2019 and 2018, respectively. We exclude fair value changes related to the forward rate from our hedging relationship and will amortize 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 gains of $2.9 million and $7.3 million as of December 31, 2019 and 2018, respectively.

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	2019		2018			Location	2019		2018		Location	2019		2018
Gains (losses) on net investment hedge	$	25.3	$	(3.8	)	Gains (losses) on net investment hedge	$	3.3	$	—	Other income (expense)	$	7.0	$	1.5

For additional information on our collaboration arrangements with Samsung Bioepis, please read Note 18, 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 contracts as of December 31, 2019 and 2018, were $793.8 million and $735.1 million, respectively. Net losses of $5.9 million and net gains of $2.0 million and $4.5 million related to these contracts were recorded as a component of other income (expense), net, for the years ended December 31, 2019, 2018 and 2017, 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:



(In millions)	Balance Sheet Location	Fair Value As of December 31, 2019		Fair Value As of December 31, 2018
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	33.8	$	65.8
Liability derivative instruments	Accrued expenses and other	$	2.0	$	6.9
	Other long-term liabilities	$	1.7	$	—
Net Investment Hedging Instruments:
Asset derivative instruments	Other current assets	$	2.0	$	—
Fair Value Hedging Instruments
Liability derivative instruments	Accrued expenses and other	$	2.3	$	—
	Other long-term liabilities	$	—	$	14.5
Other Derivative Instruments:
Asset derivative instruments	Other current assets	$	8.0	$	1.1
Liability derivative instruments	Accrued expenses and other	$	2.4	$	3.2

Share-based Payments

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Share-based Payments

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)	2019			2018			2017
Research and development	$	77.1		$	75.8		$	74.0
Selling, general and administrative	148.3			105.8			95.7
Subtotal	225.4			181.6			169.7
Capitalized share-based compensation costs	(8.9		)	(11.5		)	(9.6		)
Share-based compensation expense included in total cost and expenses	216.5			170.1			160.1
Income tax effect	(35.7		)	(27.5		)	(42.8		)
Share-based compensation expense included in net income attributable to Biogen Inc.	$	180.8		$	142.6		$	117.3

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)	2019			2018			2017
Market stock units	$	30.4		$	27.2		$	22.4
Time-vested restricted stock units	134.0			126.6			107.3
Cash settled performance units	0.7			7.8			18.4
Performance units	1.6			3.1			12.3
Performance stock units settled in stock	15.5			4.7			—
Performance stock units settled in cash	5.5			1.7			—
Employee stock purchase plan	11.5			10.5			9.3
NST stock options	26.2			—			—
Subtotal	225.4			181.6			169.7
Capitalized share-based compensation costs	(8.9		)	(11.5		)	(9.6		)
Share-based compensation expense included in total cost and expenses	$	216.5		$	170.1		$	160.1

As of December 31, 2019, unrecognized compensation cost related to unvested share-based compensation was approximately $210.4 million, net of estimated forfeitures. We expect to recognize the cost of these unvested awards over a weighted-average period of 1.9 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 our 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

We currently do not grant stock options to our employees or directors. Outstanding stock options previously granted to our employees and directors generally have a 10-year term and vest over a period of between one and four years, provided the individual continues to serve at Biogen through the vesting dates. Options granted under all plans are exercisable at a price per share not less than the fair market value of the underlying common stock on the date of grant. As of December 31, 2019, all outstanding options were exercisable.

The following table summarizes our stock option activity:



	Shares		Weighted Average Exercise Price
Outstanding at December 31, 2018	27,000		$	53.82
Granted	—		$	—
Exercised	(15,000	)	$	50.03
Cancelled	—		$	—
Outstanding at December 31, 2019	12,000		$	58.46

The total intrinsic values of options exercised in 2019, 2018 and 2017 totaled $4.2 million, $4.0 million and $3.4 million, respectively. The aggregate intrinsic values of options outstanding as of December 31, 2019, totaled $2.9 million. The weighted average remaining contractual term for options outstanding as of December 31, 2019, was 0.2 years.

The following table summarizes the amount of tax benefit realized for stock options and cash received from the exercise of stock options:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Tax benefit realized for stock options	$	2.5	$	2.2	$	3.4
Cash received from the exercise of stock options	$	0.4	$	0.8	$	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 0% and 150% 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 0% and 200% 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.

The following table summarizes our MSU activity:



	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	180,000		$	371.32
Granted (a)	147,000		$	378.08
Vested	(101,000	)	$	356.71
Forfeited	(43,000	)	$	388.68
Unvested at December 31, 2019	183,000		$	378.09

(a)

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,
	2019	2018	2017
Expected dividend yield	—%	—%	—%
Range of expected stock price volatility	31.2% - 33.6%	27.5% - 32.4%	33.0% - 35.6%
Range of risk-free interest rates	2.46% - 2.53%	1.9% - 2.3%	0.9% - 1.6%
30 calendar day average stock price on grant date	$228.59 - $331.18	$279.47 - $346.76	$263.18 - $267.88
Weighted-average per share grant date fair value	$378.08	$378.85	$382.59

The fair values of MSUs vested in 2019, 2018 and 2017 totaled $32.5 million, $26.9 million and $31.4 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 0% and 200% 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.

The following table summarizes our CSPU activity:



	Shares
Unvested at December 31, 2018	50,000
Granted	—
Vested	(33,000	)
Forfeited	(4,000	)
Unvested at December 31, 2019	13,000

The cash paid in settlement of CSPUs vested in 2019, 2018 and 2017 totaled $10.6 million, $15.1 million and $16.6 million, respectively.

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 0% and 200% 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.

The following table summarizes our PU activity:



	Shares
Unvested at December 31, 2018	48,000
Granted	—
Vested	(33,000	)
Forfeited	(4,000	)
Unvested at December 31, 2019	11,000

All PUs that vested in 2019, 2018 and 2017 were settled in cash totaling $10.4 million, $17.0 million and $11.5 million, respectively.

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.

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



	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2018	60,000		$	317.26
Granted (a)	77,000		$	316.28
Vested	—		$	—
Forfeited	(26,000	)	$	318.11
Unvested at December 31, 2019	111,000		$	316.39


(a)	PSUs settled in stock granted in 2019 include awards granted in conjunction with our annual awards made in February 2019 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.

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 0% and 200% 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.

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



	Shares
Unvested at December 31, 2018	40,000
Granted (a)	63,000
Vested	(1,000	)
Forfeited	(20,000	)
Unvested at December 31, 2019	82,000


(a)	PSUs settled in cash granted in 2019 include awards granted in conjunction with our annual awards made in February 2019 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.

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, 2018	903,000		$	303.18
Granted (a)	602,000		$	304.44
Vested	(416,000	)	$	294.71
Forfeited	(151,000	)	$	311.07
Unvested at December 31, 2019	938,000		$	306.55


(a)	RSUs granted in 2019 primarily represent RSUs granted in conjunction with our annual awards made in February 2019 and awards made in conjunction with the hiring of new employees. RSUs granted in 2019 also include approximately 15,000 RSUs granted to our Board of Directors.

RSUs granted in 2018 and 2017 had weighted average grant date fair values of $316.32 and $293.41, respectively.

The fair values of RSUs vested in 2019, 2018 and 2017 totaled $131.5 million, $111.7 million and $100.0 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)	2019		2018		2017
Shares issued under the 2015 ESPP	204,000		170,000		167,000
Cash received under the 2015 ESPP	$	40.4	$	40.5	$	39.8

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 2,913.7	$ 1,224.6
Marketable securities	1,562.2	2,313.4
Accounts receivable, net	1,880.5	1,958.5
Due from anti-CD20 therapeutic programs	590.2	526.9
Inventory	804.2	929.9
Other current assets	631.0	687.6
Total current assets	8,381.8	7,640.9
Marketable securities	1,408.1	1,375.9
Property, plant and equipment, net	3,247.3	3,601.2
Operating lease assets	427.0	0.0
Intangible assets, net	3,527.4	3,120.0
Goodwill	5,757.8	5,706.4
Deferred tax asset	3,232.1	2,153.9
Investments and other assets	1,252.8	1,690.6
Total assets	27,234.3	25,288.9
Current liabilities:
Current portion of notes payable	1,495.8	0.0
Taxes payable	71.4	63.5
Accounts payable	530.8	370.5
Accrued expenses and other	2,765.8	2,861.2
Total current liabilities	4,863.8	3,295.2
Notes payable	4,459.0	5,936.5
Deferred tax liability	2,810.8	1,636.2
Operating lease liability, noncurrent	412.7	0.0
Other long-term liabilities	1,348.9	1,389.4
Total liabilities	13,895.2	12,257.3
Commitments and contingencies
Biogen Idec Inc. shareholders' equity
Preferred stock, par value $0.001 per share	0.0	0.0
Common stock, par value $0.0005 per share	0.1	0.1
Additional paid-in capital	0.0	0.0
Accumulated other comprehensive loss	(135.2)	(240.4)
Retained earnings	16,455.4	16,257.0
Treasury stock, at cost; 23.8 million and 23.8 million shares, respectively	(2,977.1)	(2,977.1)
Total Biogen Inc. shareholders’ equity	13,343.2	13,039.6
Noncontrolling interests	(4.1)	(8.0)
Total equity	13,339.1	13,031.6
Total liabilities and equity	$ 27,234.3	$ 25,288.9

Acquisitions Acquisitions (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jun. 07, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 5,757.8		$ 5,706.4	$ 4,632.5
Nightstar
Business Acquisition [Line Items]
Cash and Equivalents		$ 107.8
Marketable Securities		7.5
In-process research and development		700.0
Goodwill		117.5
Deferred Tax Liability		(81.9)
Other, net		1.3
Total purchase price		$ 852.2

Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Income Taxes (Details Textual) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Deferred tax assets, other		$ 103.7	$ 38.9
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent		(4.50%)	(1.90%)	(11.10%)
Statutory rate		21.00%	21.00%	35.00%
Income tax benefit (expense)		$ 1,158.0	$ 1,425.6	$ 2,458.7
Income Taxes Paid		87.0
Deferred tax liabilities, temporary differences, purchase accounting, foreign subsidiaries		1,500.0
GILTI		(1,381.6)	(544.6)
Net impairment on certain tax assets	$ 48.8			48.8
Decrease in Unrecognized Tax Benefits is Reasonably Possible		75.0
Income Taxes (Textual)
Total deferred charges and prepaid taxes		243.8	239.2
Unrecognized tax benefit	64.3	122.7	109.1	64.3
Net interest expense		4.7	2.2	4.8
Unrecognized Tax Benefits, Interest on Income Taxes Accrued		20.0	$ 13.8
2017 Tax Act
Tax Credit Carryforward [Line Items]
Statutory rate			21.00%
Income tax benefit (expense)				1,200.0
Transition toll tax liabilities	989.6	697.0		989.6
Income tax expense (benefit)	184.0		$ 12.7
Reduction in deferred tax liability, undistributed foreign earnings			34.6
GILTI			135.8
Other tax expense (benefit)			$ 11.0
General Business \| Domestic Country
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards		0.7
Tax Credit Carryforward, Amount		1.3
General Business \| State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local		4.6
General Business \| Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards		1,773.8
Research \| State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount		133.8
Prepaid taxes
Tax Credit Carryforward [Line Items]
Net impairment on certain tax assets	$ 142.6			$ 142.6
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%			15.50%
Other Foreign Earnings \| 2017 Tax Act
Tax Credit Carryforward [Line Items]
Transition Toll Tax repatriation tax rate	8.00%			8.00%
ZINBRYTA
Tax Credit Carryforward [Line Items]
Unrecorded tax benefit				$ 93.8
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
Denmark Manufacturing Operations
Tax Credit Carryforward [Line Items]
Tax expense on disposal group		68.9
Intellectual Property
Tax Credit Carryforward [Line Items]
Deferred Tax Liabilities, Other		603.3
Deferred tax assets, other		$ 754.1

Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 2,541.1	$ 705.5
Commercial Paper
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	384.4	231.2
Overnight Reverse Repurchase Agreements
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	368.8	0.0
Money Market Funds
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	1,628.5	279.5
Short-term Debt Securities
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 159.4	$ 194.8

Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Income tax benefit (expense)		$ 1,158.0	$ 1,425.6	$ 2,458.7
Accumulated impairment losses related to goodwill		0.0
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period		5,706.4	4,632.5
Increase to goodwill		117.5	1,080.1
Elimination of goodwill allocated to Hillerød, Denmark manufacturing operations		69.5	0.0
Other		3.4	(6.2)
Goodwill, end of period	$ 5,706.4	$ 5,757.8	5,706.4	$ 4,632.5
Fumapharm AG \| TECFIDERA
Goodwill [Line Items]
Income tax benefit (expense)			119.9
Summary of roll forward of the changes in goodwill
Increase to goodwill	300.0		1,200.0
Each additional one billion up to twenty billion \| Fumapharm AG \| TECFIDERA
Goodwill [Line Items]
Cumulative sales level	$ 20,000.0		$ 20,000.0

Indebtedness

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Indebtedness

Our indebtedness is summarized as follows:



	As of December 31,
(In millions)	2019		2018
Current portion:
2.900% Senior Notes due September 15, 2020	$	1,495.8	$	—
Current portion of notes payable	$	1,495.8	$	—
Non-current portion:
2.900% Senior Notes due September 15, 2020	—		1,480.8
3.625% Senior Notes due September 15, 2022	996.6		995.5
4.050% Senior Notes due September 15, 2025	1,739.5		1,737.8
5.200% Senior Notes due September 15, 2045	1,722.9		1,722.4
Non-current portion of notes payable	$	4,459.0	$	5,936.5

2015 Senior Notes

The following is a summary of our principal indebtedness as of December 31, 2019:


•	$1.5 billion aggregate principal amount of 2.90% Senior Notes due September 15, 2020, valued at 99.792% of par;


•	$1.0 billion aggregate principal amount of 3.625% Senior Notes due September 15, 2022, valued at 99.920% of par;


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


•	$1.75 billion aggregate principal amount of 5.20% Senior Notes due September 15, 2045, valued at 99.294% of par.

The costs associated with these offerings 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.

These notes are senior unsecured obligations. These Senior Notes may be redeemed at our option at any time at 100% of the principal amount plus accrued interest and a specified make-whole amount. These Senior Notes contain a change of control provision that may require us to purchase the notes at a price equal to 101% of the principal amount plus accrued and unpaid interest to the date of purchase under certain circumstances.

In connection with the 2.90% Senior Notes offering due in 2020, we entered into interest rate swap contracts. The carrying value of the 2.90% Senior Notes as of December 31, 2019 and 2018, includes approximately $2.3 million and $14.5 million, respectively, related to changes in the fair value of these contracts. For additional information on our interest rate contracts, please read Note 9, Derivative Instruments, to these consolidated financial statements.

2015 Credit Facility

In August 2015 we entered into a $1.0 billion, five-year senior unsecured revolving credit facility under which we were permitted to draw funds for working capital and general corporate purposes. The terms of the revolving credit facility included a financial covenant that required us not to exceed a maximum consolidated leverage ratio. As of December 31, 2019, we had no outstanding borrowings and were in compliance with all covenants under this facility.

In January 2020 we entered into a new $1.0 billion, five-year senior unsecured revolving credit facility that replaced the credit facility entered into in August 2015. For additional information, please read Note 26, Subsequent Events, to these consolidated financial statements.

Debt Maturity

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



(In millions)	As of December 31, 2019
2020	$	1,500.0
2021	—
2022	1,000.0
2023	—
2024	—
2025 and thereafter	3,500.0
Total	$	6,000.0

The fair value of our debt is disclosed in Note 7, Fair Value Measurements, to these consolidated financial statements.

Divestitures Divestitures (Details Textual) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 01, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on divestiture of Hillerød, Denmark manufacturing operations			$ 55.3	$ 0.0	$ 0.0
Inventory raw materials sold to FUJIFILM						$ 41.8
Denmark Manufacturing Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received for sale of Denmark manufacturing operations						$ 881.9
Future minimum batch production for Denmark manufacturing operations	$ 74.0	$ 114.0	74.0
Loss on divestiture of Hillerød, Denmark manufacturing operations, net of tax	$ 40.2	164.4	124.2
Loss on divestiture of Hillerød, Denmark manufacturing operations		$ 95.5	55.3
Expected costs to sell disposal group			11.2
Tax expense on disposal group			$ 68.9

- Definition

Amount of tax expense (benefit) related to a discontinued operation. Includes, but is not limited to, tax expense (benefit) related to income (loss) from operations during the phase-out period, tax expense (benefit) related to gain (loss) on disposal, tax expense (benefit) related to gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and tax expense (benefit) related to adjustments of a prior period gain (loss) on disposal.

+ References + Details

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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% on annual worldwide net commercial sales up to $2.0 billion and 25% 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% and 15%, 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 18, Collaborative and Other Relationships, to these consolidated financial statements. VUMERITY In October 2019 the FDA approved VUMERITY for the treatment of RMS. Under our agreement with Alkermes, we make royalty payments to Alkermes on worldwide net commercial sales of VUMERITY using a royalty rate of 15%, 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 18, Collaborative and Other Relationships, to these consolidated financial statements. Contingent Consideration related to Business Combinations In connection with our acquisitions of Convergence and BIN, we agreed to make additional payments based upon the achievement of certain milestone events. As the acquisitions of Convergence and BIN occurred after January 1, 2009, we recognized the contingent consideration liabilities associated with these transactions at their fair value on the acquisition date and revalue the remaining obligations each reporting period. We may pay up to approximately $735.0 million in remaining milestones related to these acquisitions. Fumapharm AG In 2006 we acquired Fumapharm AG. As part of this acquisition we acquired the Fumapharm Products. We were required to make contingent payments to former shareholders of Fumapharm AG and holders of their rights based on the attainment of certain cumulative sales levels of Fumapharm Products and the level of total net sales of Fumapharm Products in the prior 12-month period, as defined in the acquisition agreement, until such time as the cumulative sales level reached $20.0 billion, at which time no further contingent payments were due. During the first quarter of 2019 we paid the final $300.0 million contingent payment as we achieved the $20.0 billion cumulative sales levels related to the Fumapharm Products in the fourth quarter of 2018. Contingent Development, Regulatory and Commercial Milestone Payments Based on our development plans as of December 31, 2019, we could make potential future milestone payments to third parties of up to approximately $6.8 billion, including approximately $1.2 billion in development milestones, approximately $1.4 billion in regulatory milestones and approximately $4.2 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, 2019, 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. Provided various development, regulatory or commercial milestones are achieved, we anticipate that we may pay approximately $430.0 million of milestone payments in 2020, including $75.0 million upon the regulatory filing with the FDA for approval of aducanumab and $100.0 million if aducanumab is launched in the U.S. Other Funding Commitments As of December 31, 2019, 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 expenses of approximately $24.0 million in our consolidated balance sheet for expenditures incurred by CROs as of December 31, 2019. We have approximately $514.0 million in cancellable future commitments based on existing CRO contracts as of December 31, 2019. As part of the sale of our Hillerød, Denmark manufacturing operations to FUJIFILM, we have provided FUJIFILM with certain minimum batch production commitment guarantees. There is a risk that the minimum contractual batch production commitments will not be met. Based upon current estimates we expect to incur an adverse commitment obligation of approximately $74.0 million associated with such guarantees and have accrued for this obligation. We may adjust this estimate based upon changes in business conditions, which may result in the increase or reduction of this adverse commitment obligation in subsequent periods. 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, 2019, we have $136.9 million of net liabilities associated with uncertain tax positions. As of December 31, 2019 and 2018, we have accrued income tax liabilities of $697.0 million under the Transition Toll Tax. Of the amounts accrued as of December 31, 2019, no amounts are expected to be paid within one year due to an approximately $87.0 million carryforward of taxes paid in relation to the company's 2017 tax return. The Transition Toll Tax will be paid 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 16, Income Taxes, to these consolidated financial statements. Solothurn, Switzerland Manufacturing Facility In order to support our drug development pipeline, we are building a large-scale biologics manufacturing facility in Solothurn, Switzerland. We expect this facility to be partially operational by the end of 2020. As of December 31, 2019, we had contractual commitments of approximately $52.0 million related to the construction of this facility.

Acquisitions

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

Acquisitions

Acquisition of Nightstar Therapeutics plc

In June 2019 we completed our acquisition of all of the outstanding shares of Nightstar Therapeutics plc (NST), a clinical-stage gene therapy company focused on adeno-associated virus treatments for inherited retinal disorders. As a result of this acquisition, we added two mid- to late-stage clinical assets, as well as preclinical programs, in ophthalmology. These assets include BIIB111 (timrepigene emparvovec), which is in Phase 3 development for the potential treatment of choroideremia, a rare, degenerative, X-linked inherited retinal disorder that leads to blindness and currently has no approved treatments, and BIIB112 (RPGR gene therapy), which is in Phase 2/3 development for the potential treatment of X-linked retinitis pigmentosa, which is a rare inherited retinal disease with no currently approved treatments.

Under the terms of the acquisition, we paid NST shareholders $25.50 in cash for each issued and outstanding NST share, which totaled $847.6 million. In addition, we paid $4.6 million in cash for equity compensation, which is attributable to pre-combination services and is reflected as a component of the total purchase price paid. The fair value of equity compensation attributable to the post-combination service period was $26.2 million, of which $18.4 million was recognized as a charge to selling, general and administrative expense with the remaining $7.8 million as a charge to research and development expense in our consolidated statements of income. These amounts were associated with the accelerated vesting of stock options previously granted to NST employees and were fully paid in cash as of June 30, 2019. We funded this acquisition through available cash and accounted for it as an acquisition of a business.

We finalized purchase accounting for this acquisition in the fourth quarter of 2019. The following table summarizes the fair values of the separately identifiable assets acquired and liabilities assumed:



(In millions)
Cash and cash equivalents	$	107.8
Marketable securities	7.5
In-process research and development intangible assets	700.0
Goodwill	117.5
Deferred tax liability	(81.9		)
Other, net	1.3
Total purchase price	$	852.2

The fair value of the IPR&D programs acquired was determined through a probability adjusted discounted cash flow analysis utilizing a discount rate of 12.5%. This valuation was primarily driven by the value associated with BIIB111. The fair value associated with BIIB111 was $480.0 million. We have recorded an additional IPR&D asset related to BIIB112 of $220.0 million. Some of the more significant assumptions utilized in our asset valuations included the estimated net cash flows for each year for each asset or product, including net revenues, cost of sales, research and development and other operating expenses, the potential regulatory and commercial success risks, competitive trends impacting the asset and each cash flow stream as well as other factors. These fair value measurements were based on significant inputs not observable in the market and thus represent Level 3 fair value measurements.

We have recognized goodwill in relation to the fair value associated with NST workforce's expertise and early research in retinal disorders. We also recognized goodwill in relation to the establishment of a deferred tax liability for the acquired IPR&D intangible assets, which have no tax basis. This deferred tax liability is net of the related impacts on the deferred taxes for GILTI. Goodwill that is tax deductible for GILTI purposes is approximately $35.5 million.

Pro forma results of operations as a result of this acquisition have not been presented as this acquisition is not material to our consolidated statements of income. Subsequent to June 7, 2019, the acquisition date, our results of operations include the results of operations of NST.

BIIB100 Acquisition

In January 2018 we acquired BIIB100 (XP01 inhibitor) from Karyopharm Therapeutics Inc. (Karyopharm). BIIB100 is a Phase 1 investigational oral compound for the treatment of certain neurological and neurodegenerative diseases, primarily in ALS. BIIB100 is a novel therapeutic candidate that works by inhibiting a protein known as XPO1, with the goal of reducing inflammation and neurotoxicity, along with increasing neuroprotective responses.

We accounted for this transaction as an asset acquisition as the value being acquired primarily relates to a single asset. In connection with the closing of this transaction, we made an upfront payment of $10.0 million to Karyopharm, which was recorded as acquired IPR&D in our consolidated statements of income as BIIB100 had not yet reached technological feasibility. We may also pay Karyopharm up to $207.0 million in additional milestone payments as well as tiered royalties on potential net commercial sales in the mid-single digit to low-teen percentages.

BIIB104 Acquisition

In April 2018 we acquired BIIB104 (AMPA) from Pfizer Inc. (Pfizer). BIIB104 is a first-in-class, Phase 2b ready AMPA receptor potentiator for cognitive impairment associated with schizophrenia. AMPA receptors mediate fast excitatory synaptic transmission in the central nervous system, a process which can be disrupted in a number of neurological and psychiatric diseases, including schizophrenia.

We accounted for this transaction as an asset acquisition as the value being acquired primarily relates to a single asset. In connection with the closing of this transaction, we made an upfront payment of $75.0 million to Pfizer, which was recorded as acquired IPR&D in our consolidated statements of income as BIIB104 had not yet reached technological feasibility. We may also pay Pfizer up to $515.0 million in additional development and commercialization milestone payments as well as tiered royalties on potential net commercial sales in the low to mid-teen percentages.

TMS Co., Ltd.

In June 2018 we entered into an exclusive option agreement with TMS Co., Ltd. (TMS) granting us the option to acquire TMS-007, a plasminogen activator with a novel mechanism of action associated with breaking down blood clots, which is in Phase 2 development in Japan, and backup compounds for the treatment of stroke. In exchange for the purchase option, we made a $4.0 million upfront payment to TMS, which was recorded as research and development expense in our consolidated statements of income as TMS-007 had not yet reached technological feasibility.

If we exercise the purchase option, we will make an additional payment of $18.0 million upon closing of the asset acquisition, which will be recorded as acquired IPR&D expense in our consolidated statements of income as TMS-007 will not have reached technological feasibility at that time. In addition, we may pay TMS up to $335.0 million in additional development and commercialization milestone payments as well as tiered royalties on potential net commercial sales in the high-single digit to low-teen percentages. If we exercise the purchase option, consummation of the asset acquisition may be subject to the expiration of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 in the U.S.

BIIB110 Acquisition

In July 2018 we acquired BIIB110 (ActRIIA/B ligand trap) and ALG-802 from AliveGen Inc. (AliveGen). BIIB110 and ALG-802 represent novel ways of targeting the myostatin pathway. We initially plan to study BIIB110 in multiple neuromuscular indications, including SMA and ALS.

We accounted for this transaction as an asset acquisition as the value being acquired primarily relates to a single asset. In connection with the closing of this transaction, we made an upfront payment of $27.5 million to AliveGen, which was recorded as acquired IPR&D in our consolidated statements of income as BIIB110 had not yet reached technological feasibility. We may also pay AliveGen up to $535.0 million in additional development and commercialization milestones.

BIIB093 Acquisition

In May 2017 we acquired BIIB093 (glibencamide IV) from Remedy Pharmaceuticals Inc. (Remedy). BIIB093 is in a Phase 3 study for large hemispheric infarction (LHI), a severe form of ischemic stroke where brain swelling (cerebral edema) often leads to a disproportionately large share of stroke-related morbidity and mortality. The U.S. Food and Drug Administration (FDA) granted BIIB093 orphan drug designation for severe cerebral edema in patients with acute ischemic stroke. The FDA has also granted BIIB093 fast track designation.

We are responsible for the future development and commercialization of BIIB093 and Remedy may share in the cost of development for the target indication for BIIB093 in LHI stroke.

We accounted for this transaction as an asset acquisition as we did not acquire any employees from Remedy nor did we acquire any significant processes required in the development of BIIB093. In connection with the closing of this transaction, we made an upfront payment of $120.0 million to Remedy, which was recorded as acquired IPR&D in our consolidated statements of income as BIIB093 had not yet reached technological feasibility. We may also pay Remedy certain development and sales based milestone payments that are substantially payable upon or after regulatory approval, as well as royalties on potential net commercial sales.

Share-Based Payments (Details 10) - Time-vested restricted stock units - $ / shares

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Time-vested restricted stock units

Beginning Balance, Unvested, Shares

903,000

Beginning Balance, Weighted Average Grant Date Fair Value

$ 303.18

Shares, Granted

^[1]

602,000

Weighted Average Grant Date Fair Value, Granted

$ 304.44

^[1]

$ 316.32

$ 293.41

Shares, Vested

(416,000)

Weighted Average Grant Date Fair Value, Vested

$ 294.71

Shares, Forfeited

(151,000)

Weighted Average Grant Date Fair Value, Forfeited

$ 311.07

Ending Balance, Unvested, Shares

938,000

903,000

Ending Balance, Weighted Average Grant Date Fair Value

$ 306.55

$ 303.18

[1]	RSUs granted in 2019 primarily represent RSUs granted in conjunction with our annual awards made in February 2019 and awards made in conjunction with the hiring of new employees. RSUs granted in 2019 also include approximately 15,000 RSUs granted to our Board of Directors.

Revenues

12 Months Ended

Dec. 31, 2019

Revenue from Contract with Customer [Abstract]

Revenues

Product Revenues

Revenues by product are summarized as follows:



	For the Years Ended December 31,
	2019						2018						2017
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis (MS):
TECFIDERA	$	3,306.5	$	1,126.2	$	4,432.7	$	3,253.2	$	1,020.9	$	4,274.1	$	3,294.0	$	920.0	$	4,214.0
Interferon*	1,426.6		675.2		2,101.8		1,668.3		694.7		2,363.0		1,889.1		756.7		2,645.8
TYSABRI	1,041.8		850.4		1,892.2		1,025.0		839.0		1,864.0		1,113.8		859.3		1,973.1
VUMERITY	5.5		—		5.5		—		—		—		—		—		—
FAMPYRA	—		97.1		97.1		—		92.7		92.7		—		91.6		91.6
ZINBRYTA	—		—		—		—		1.4		1.4		—		52.7		52.7
Subtotal: MS Product Revenues	5,780.4		2,748.9		8,529.3		5,946.5		2,648.7		8,595.2		6,296.9		2,680.3		8,977.2

Spinal Muscular Atrophy:
SPINRAZA	933.4		1,163.6		2,097.0		854.0		870.2		1,724.2		657.0		226.7		883.7

Biosimilars:
BENEPALI	—		486.2		486.2		—		485.2		485.2		—		370.8		370.8
IMRALDI	—		184.0		184.0		—		16.7		16.7		—		—		—
FLIXABI	—		68.1		68.1		—		43.2		43.2		—		9.0		9.0
Subtotal: Biosimilar product revenues	—		738.3		738.3		—		545.1		545.1		—		379.8		379.8

Other:
FUMADERM	—		15.2		15.2		—		22.3		22.3		—		39.6		39.6

Hemophilia:
ELOCTATE	—		—		—		—		—		—		42.2		6.2		48.4
ALPROLIX	—		—		—		—		—		—		21.0		5.0		26.0
Subtotal: Hemophilia product revenues	—		—		—		—		—		—		63.2		11.2		74.4

Total product revenues	$	6,713.8	$	4,666.0	$	11,379.8	$	6,800.5	$	4,086.3	$	10,886.8	$	7,017.1	$	3,337.6	$	10,354.7

*Interferon includes AVONEX and PLEGRIDY.

We recognized revenues from two wholesalers accounting for 30% and 17% of gross product revenues in 2019, 32% and 18% of gross product revenues in 2018 and 34% and 21% of gross product revenues in 2017, respectively.

As of December 31, 2019, two wholesale distributors individually accounted for approximately 24.1% and 13.9% of net accounts receivable associated with our product sales, as compared to 27.7% and 15.6% as of December 31, 2018, respectively.

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



(In millions)	Discounts			Contractual Adjustments			Returns			Total
2019
Beginning balance	$	127.8		$	888.8		$	34.7		$	1,051.3
Current provisions relating to sales in current year	666.2			3,011.5			20.9			3,698.6
Adjustments relating to prior years	0.3			(54.1		)	5.5			(48.3		)
Payments/returns relating to sales in current year	(535.5		)	(2,242.9		)	(0.2		)	(2,778.6		)
Payments/returns relating to sales in prior years	(127.7		)	(576.0		)	(20.4		)	(724.1		)
Ending balance	$	131.1		$	1,027.3		$	40.5		$	1,198.9



(In millions)	Discounts			Contractual Adjustments			Returns			Total
2018
Beginning balance	$	109.6		$	606.0		$	46.0		$	761.6
Current provisions relating to sales in current year	679.3			2,686.7			23.1			3,389.1
Adjustments relating to prior years	(0.3		)	(10.0		)	(1.8		)	(12.1		)
Payments/returns relating to sales in current year	(551.7		)	(1,887.6		)	(1.1		)	(2,440.4		)
Payments/returns relating to sales in prior years	(109.1		)	(506.3		)	(31.5		)	(646.9		)
Ending balance	$	127.8		$	888.8		$	34.7		$	1,051.3



(In millions)	Discounts			Contractual Adjustments			Returns			Total
2017
Beginning balance	$	71.6		$	482.7		$	51.2		$	605.5
Current provisions relating to sales in current year	583.0			2,307.4			26.9			2,917.3
Adjustments relating to prior years	(0.1		)	15.0			(8.9		)	6.0
Payments/returns relating to sales in current year	(475.8		)	(1,756.9		)	(0.1		)	(2,232.8		)
Payments/returns relating to sales in prior years	(69.1		)	(442.2		)	(23.1		)	(534.4		)
Ending balance	$	109.6		$	606.0		$	46.0		$	761.6

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



	As of December 31,
(In millions)	2019		2018
Reduction of accounts receivable	$	197.8	$	176.6
Component of accrued expenses and other	1,001.1		874.7
Total revenue-related reserves	$	1,198.9	$	1,051.3

Revenues from Anti-CD20 Therapeutic Programs

Revenues from anti-CD20 therapeutic programs are 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)	2019		2018		2017
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses	$	1,542.4	$	1,431.9	$	1,316.4
Other revenues from anti-CD20 therapeutic programs	748.0		548.3		242.8
Total revenues from anti-CD20 therapeutic programs	$	2,290.4	$	1,980.2	$	1,559.2

Approximately 16%, 15% and 13% of our total revenues in 2019, 2018 and 2017, respectively, are derived from our collaboration arrangements with Genentech. For additional information on our collaboration arrangements with Genentech, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Other Revenues

Other revenues are summarized as follows:



	For the Years Ended December 31,
(In millions)	2019		2018			2017
Revenues from collaborative and other relationships:
(Loss) profit earned under our 50% share of the co-promotion losses on ZINBRYTA in the U.S. with AbbVie Inc.	$	—	$	(8.6	)	$	(16.9	)
Revenues earned under our technical development services and manufacturing service agreements and royalty revenues on biosimilar products with Samsung Bioepis	106.2		96.4			42.7
Revenues earned under manufacturing services agreement on shipments of ELOCTA and ALPROLIX to Swedish Orphan Biovitrum AB (Sobi) and royalties from Sobi on sales of ELOCTA and ALPROLIX	—		—			10.7
Other royalty and corporate revenues:
Royalty	17.0		38.7			69.8
Other corporate	584.5		459.4			253.7
Total other revenues	$	707.7	$	585.9		$	360.0

Other corporate revenues primarily reflect amounts earned under contract manufacturing agreements with our strategic customers, including Bioverativ Inc. (Bioverativ). During the years ended December 31, 2019, 2018 and 2017, we recognized $383.2 million, $206.7 million and $64.8 million, respectively, in revenues under the manufacturing and supply agreement with Bioverativ entered into in connection with the spin-off of our hemophilia business.

During the third quarter of 2019 we amended our agreement with a contract manufacturing customer. Under the amended agreement, we will license certain of our manufacturing-related intellectual property to the customer. We will be eligible to receive $500.0 million in a series of three payments. The first payment is due upon a regulatory achievement related to the customer's product manufactured using our manufacturing-related intellectual property, with subsequent payments payable upon the first and second anniversaries of the regulatory achievement. We expect the regulatory achievement to occur in 2020. If we earn this payment, we expect to allocate the consideration between the license for the manufacturing-related intellectual property and the manufacturing product supply services.

For additional information on our collaboration arrangements with AbbVie Inc. (AbbVie) and Samsung Bioepis, please read Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

Acquisitions (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended					12 Months Ended
	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 07, 2019
Business Acquisition [Line Items]
Acquired in-process research and development						$ 0.0	$ 112.5	$ 120.0
Nightstar
Business Acquisition [Line Items]
Price per share									$ 25.50
Total transaction value	$ 847.6
Payments for pre-combination equity compensation	4.6
Fair value, in-process research and development, discount rate									12.50%
In-process research and development									$ 700.0
Deferred tax liabilities, goodwill	35.5
Karyopharm
Business Acquisition [Line Items]
Acquired in-process research and development				$ 10.0
Estimated additional payments upon achievement of development and commercial milestones						207.0
Pfizer
Business Acquisition [Line Items]
Acquired in-process research and development			$ 75.0
Estimated additional payments upon achievement of development and commercial milestones						515.0
TMS
Business Acquisition [Line Items]
Acquired in-process research and development						18.0
Estimated additional payments upon achievement of development and commercial milestones						335.0
Research and development expense asset acquired			$ 4.0
AliveGen
Business Acquisition [Line Items]
Acquired in-process research and development		$ 27.5
Estimated additional payments upon achievement of development and commercial milestones						$ 535.0
Remedy Pharmaceutical
Business Acquisition [Line Items]
Acquired in-process research and development					$ 120.0
Post-acquisition equity compensation \| Nightstar
Business Acquisition [Line Items]
Fair-value post-combination equity compensation	26.2
Selling, General and Administrative Expenses \| Nightstar
Business Acquisition [Line Items]
Fair-value post-combination equity compensation	18.4
Research and development \| Nightstar
Business Acquisition [Line Items]
Fair-value post-combination equity compensation	$ 7.8
BIIB111 \| Nightstar
Business Acquisition [Line Items]
In-process research and development									480.0
BIIB112 \| Nightstar
Business Acquisition [Line Items]
In-process research and development									$ 220.0

Equity (Details) - shares shares in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of common stock
Common stock, shares authorized	1,000.0	1,000.0	1,000.0
Common stock, shares issued	198.0	221.0	235.3
Common stock, shares outstanding	174.2	197.2	211.5

Indebtedness (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Summary of Indebtedness

Our indebtedness is summarized as follows:



	As of December 31,
(In millions)	2019		2018
Current portion:
2.900% Senior Notes due September 15, 2020	$	1,495.8	$	—
Current portion of notes payable	$	1,495.8	$	—
Non-current portion:
2.900% Senior Notes due September 15, 2020	—		1,480.8
3.625% Senior Notes due September 15, 2022	996.6		995.5
4.050% Senior Notes due September 15, 2025	1,739.5		1,737.8
5.200% Senior Notes due September 15, 2045	1,722.9		1,722.4
Non-current portion of notes payable	$	4,459.0	$	5,936.5

Total debt maturities

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



(In millions)	As of December 31, 2019
2020	$	1,500.0
2021	—
2022	1,000.0
2023	—
2024	—
2025 and thereafter	3,500.0
Total	$	6,000.0

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Segment Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Major Customer [Line Items]
Product Revenues	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
Geographic information
Long-lived assets	3,674.3				3,601.2				3,674.3	3,601.2	3,182.4
U.S
Geographic information
Long-lived assets	1,493.2				1,152.7				1,493.2	1,152.7	1,226.9
Europe
Geographic information
Long-lived assets	2,162.9				2,442.8				2,162.9	2,442.8	1,948.2
Asia
Geographic information
Long-lived assets	6.2				3.9				6.2	3.9	5.2
Other
Geographic information
Long-lived assets	12.0				1.8				12.0	1.8	2.1
Revenues from anti-cd20 therapeutic programs
Revenue, Major Customer [Line Items]
Product Revenues	600.8	595.8	576.4	517.4	534.9	511.7	490.4	443.2	2,290.4	1,980.2	1,559.2
Revenues from anti-cd20 therapeutic programs \| U.S
Revenue, Major Customer [Line Items]
Product Revenues									2,211.9	1,903.4	1,475.6
Revenues from anti-cd20 therapeutic programs \| Europe
Revenue, Major Customer [Line Items]
Product Revenues									0.2	0.2	0.6
Revenues from anti-cd20 therapeutic programs \| Asia
Revenue, Major Customer [Line Items]
Product Revenues									0.0	0.0	0.0
Revenues from anti-cd20 therapeutic programs \| Other
Revenue, Major Customer [Line Items]
Product Revenues									78.3	76.6	83.0
Other revenue
Revenue, Major Customer [Line Items]
Product Revenues	145.7	109.6	160.0	292.4	165.7	147.2	108.6	164.4	707.7	585.9	360.0
Other revenue \| U.S
Revenue, Major Customer [Line Items]
Product Revenues									585.8	457.0	249.5
Other revenue \| Europe
Revenue, Major Customer [Line Items]
Product Revenues									9.7	32.7	67.8
Other revenue \| Asia
Revenue, Major Customer [Line Items]
Product Revenues									112.2	96.2	42.7
Other revenue \| Other
Revenue, Major Customer [Line Items]
Product Revenues									0.0	0.0	0.0
Product, net
Revenue, Major Customer [Line Items]
Product Revenues	$ 2,924.8	$ 2,894.7	$ 2,880.3	$ 2,680.0	$ 2,825.7	$ 2,780.1	$ 2,757.5	$ 2,523.5	11,379.8	10,886.8	10,354.7
Product, net \| U.S
Revenue, Major Customer [Line Items]
Product Revenues									6,713.8	6,800.5	7,017.1
Product, net \| Europe
Revenue, Major Customer [Line Items]
Product Revenues									3,794.5	3,370.3	2,844.8
Product, net \| Asia
Revenue, Major Customer [Line Items]
Product Revenues									320.3	281.2	160.1
Product, net \| Other
Revenue, Major Customer [Line Items]
Product Revenues									$ 551.2	$ 434.8	$ 332.7

Guarantees	12 Months Ended
Guarantees	Dec. 31, 2019
Guarantees [Abstract]
Guarantees	Guarantees As of December 31, 2019 and 2018, 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, 2019 and 2018.

Share-Based Payments (Details 8) - Performance stock units settled in stock
shares in Thousands

12 Months Ended

Dec. 31, 2018

$ / shares

Performance stock units settled in stock

Beginning Balance, Unvested, Shares | shares

60,000

Beginning Balance, Weighted Average Grant Date Fair Value | $ / shares

$ 317.26

Shares, Granted | shares

77,000

Weighted average grant date fair value | $ / shares

$ 316.28

^[1]

Shares, Vested | shares

Weighted Average Grant Date Fair Value, Vested | $ / shares

$ 0

Shares, Forfeited | shares

(26,000)

Weighted Average Grant Date Fair Value, Forfeited | $ / shares

$ 318.11

Ending Balance, Unvested, Shares | shares

111,000

Ending Balance, Weighted Average Grant Date Fair Value | $ / shares

$ 316.39

[1]

Quarterly Financial Data (Unaudited) (Details Textual) - USD ($) shares in Millions, $ in Millions	1 Months Ended		3 Months Ended												9 Months Ended	12 Months Ended
	May 31, 2018	Oct. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2013	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Jun. 05, 2018
Schedule Of Development Milestone And Collaboration [Line Items]
Unrealized gain (loss) on strategic investments			$ 2.8	$ (4.6)	$ (174.2)	$ 376.1	$ (12.2)	$ 141.2	$ 5.4	$ (6.4)
GILTI			(1,381.6)				(544.6)									$ (1,381.6)	$ (544.6)
Loss (gain) on fair value remeasurement of contingent consideration			(2.6)	57.8	$ 20.0	$ (11.5)	(79.3)	87.9	(1.9)	5.6						63.7	12.3	$ (62.7)
Research and development																2,280.6	2,597.2	2,253.6
Acquired in-process research and development																0.0	112.5	120.0
Payments to Noncontrolling Interests																(4.3)	36.4	134.1
Loss on divestiture of Hillerød, Denmark manufacturing operations																55.3	0.0	0.0
Net income (loss) attributable to noncontrolling interests, net of tax																0.0	43.3	131.0
Income tax benefit (expense)																1,158.0	1,425.6	2,458.7
Samsung Bioepis
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development expense on 2018 Ionis Agreement			63.0
Research and development														$ 46.0
Upfront And Milestone Payments Made To Collaborative Partner			100.0
Bristol-Myers Squibb
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development												$ 300.0				144.0	97.0
iPerian
Schedule Of Development Milestone And Collaboration [Line Items]
Developmental Milestone Payment												60.0
Alkermes
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development											$ 50.0					53.5	68.7	80.3
Upfront And Milestone Payments Made To Collaborative Partner											28.0
Ionis Pharmaceuticals
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development expense on 2018 Ionis Agreement			45.0						486.2
Research and development									324.1							30.0			$ 10.0
Premium on purchase of common stock																				$ 162.1
Investment in common stock, shares purchased																				11.5
Upfront And Milestone Payments Made To Collaborative Partner											25.0
Neurimmune
Schedule Of Development Milestone And Collaboration [Line Items]
Payments to Noncontrolling Interests	$ 50.0	$ 150.0
Additional reduction in royalty rate payable on commercial sales	5.00%
Reduction in royalty rate payable on commercial sales		15.00%
TECFIDERA
Schedule Of Development Milestone And Collaboration [Line Items]
Impairment of in-licensed patent							176.8						$ 328.2
Karyopharm
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development										$ 10.0
Remedy Pharmaceutical
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development												$ 120.0
Pfizer
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development									$ 75.0
AliveGen
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development								27.5
In-process research and development
Schedule Of Development Milestone And Collaboration [Line Items]
Impairment of IPR&D				$ 215.9				$ 189.3
2017 Tax Act
Schedule Of Development Milestone And Collaboration [Line Items]
GILTI							$ 135.8										$ 135.8
Income tax benefit (expense)																		1,200.0
Transition toll tax liabilities			697.0								$ 989.6					697.0		$ 989.6
Denmark Manufacturing Operations
Schedule Of Development Milestone And Collaboration [Line Items]
Loss on divestiture of Hillerød, Denmark manufacturing operations, net of tax			$ 40.2												$ 164.4	124.2
Loss on divestiture of Hillerød, Denmark manufacturing operations															$ 95.5	55.3
Tax expense on disposal group																$ 68.9

Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018
Property, Plant and Equipment
Operating lease assets	$ 427.0	$ 0.0
Operating lease liabilities	$ 486.3
Business (Textual)
Interest in subsidiary (less than given percentage)	100.00%
Payment terms of accounts receivable arising from product sales	30 to 90 days
Estimated useful lives of leasehold improvements	Lesser of the useful life or the term of the respective lease
Purchase price of common stock under ESPP	85% of the lower of (i) the fair market value per share of the common stock on the first business day of an offering period and (ii) the fair market value per share of the common stock on the purchase date
Compensation expense over purchase period	The fair value of the look-back provision plus the 15% discount
Advertising costs	$ 79.2	90.2	$ 75.2
Minimum \| Building
Property, Plant and Equipment
Property, plant and equipment, useful life	15 years
Minimum \| Furniture and Fixtures
Property, Plant and Equipment
Property, plant and equipment, useful life	5 years
Minimum \| Machinery and Equipment
Property, Plant and Equipment
Property, plant and equipment, useful life	5 years
Minimum \| Computer Equipment
Property, Plant and Equipment
Property, plant and equipment, useful life	3 years
Maximum \| Building
Property, Plant and Equipment
Property, plant and equipment, useful life	40 years
Maximum \| Furniture and Fixtures
Property, Plant and Equipment
Property, plant and equipment, useful life	7 years
Maximum \| Machinery and Equipment
Property, Plant and Equipment
Property, plant and equipment, useful life	20 years
Maximum \| Computer Equipment
Property, Plant and Equipment
Property, plant and equipment, useful life	5 years
Accounting Standards Update 2016-16 \| Deferred Income Tax Charge
Property, Plant and Equipment
Cumulative effect of new accounting principle in period of adoption					$ 500.0
Accounting Standards Update 2016-16 \| Retained Earnings
Property, Plant and Equipment
Cumulative effect of new accounting principle in period of adoption					$ 500.0
Accounting Standards Update 2016-16 \| Deferred tax liability
Property, Plant and Equipment
Cumulative effect of new accounting principle in period of adoption		$ 400.0
Accounting Standards Update 2016-02
Property, Plant and Equipment
Operating lease assets				$ 463.0
Operating lease liabilities				$ 526.0

Litigation	12 Months Ended
Litigation	Dec. 31, 2019
Loss Contingency, Information about Litigation Matters [Abstract]
Litigation	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. 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 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, alleging that IMRALDI, the adalimumab biosimilar product of Samsung Bioepis UK Limited that Biogen has commercialized in Europe, infringes the French counterpart of European Patent No. 3 148 510 (the '510 Patent), which was issued in June 2018 and expires in May 2035. No hearing on the merits has been scheduled. In October 2018 Fresenius Kabi commenced preliminary injunction proceedings against Biogen (Denmark) Manufacturing ApS and Biogen Denmark A/S in Denmark's Maritime and Commercial High Court alleging infringement of Danish Utility Models. In June 2019 the Danish court denied Fresenius Kabi's request for a preliminary injunction and Fresenius Kabi has appealed that decision. In November 2018 Fresenius Kabi commenced infringement proceedings for damages and injunctive relief against Biogen Italia S.R.L. in the District Court of Milan relating to the Italian counterpart of the ‘510 Patent, and against Biogen GmbH in the Düsseldorf Regional Court relating to the German counterpart of the ‘510 Patent. In Italy, Fresenius Kabi has surrendered the Italian counterpart of the ‘510 Patent and has moved to dismiss its infringement action. A hearing in the proceeding in Germany has not yet been set but is expected to occur after a decision on our pending opposition to the ‘510 patent in the EPO. In July 2019 Gedeon Richter PLC (Gedeon Richter) commenced proceedings against Biogen GmbH in the Düsseldorf Regional Court alleging infringement of the German counterpart of European Patent No. 3 212 667 (the '667 Patent), which was issued in September 2018 and expires in October 2035, and seeking damages and injunctive relief. A hearing has been set for November 2020. In July 2019 Biogen Idec Ltd. (Biogen UK) and Samsung Bioepis UK Limited filed an action in the United Kingdom Patents Court to revoke the United Kingdom (U.K.) counterpart of the '667 Patent. In January 2020 the U.K. court revoked the patent. In August 2019 Biogen B.V. (Netherlands) and Samsung Bioepis UK Limited filed an action in the District Court of the Hague, Netherlands to revoke the Dutch counterpart of the '667 Patent. Gedeon Richter filed a separate action for infringement in the same court and a hearing in both cases has been set for May 2020. An estimate of the possible loss or range of loss in the pending IMRALDI patent litigation described above cannot be made at this time. Qui Tam Litigation In July 2015 a qui tam action filed by Michael Bawduniak on behalf of the U.S. and certain states was unsealed by the U.S. District Court for the District of Massachusetts. The action alleges sales and promotional activities in violation of the federal False Claims Act and state law counterparts and seeks single and treble damages, civil penalties, interest, attorneys’ fees and costs. No trial date has been set. The U.S. has not made an intervention decision. An estimate of the possible loss or range of loss cannot be made at this time. Dispute with Former Convergence Shareholders 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. Other Matters Petition for Inter Partes Review In July 2018 Mylan Pharmaceuticals, Inc. (Mylan) filed a petition that was granted by the U.S. Patent Trial and Appeal Board (PTAB) for inter partes review of our U.S. Patent No. 8,399,514 (the '514 Patent), which covers treatment of MS with 480 mg of dimethyl fumarate per day as provided for in our TECFIDERA label. Sawai USA, Inc. and Sawai Pharmaceutical Co. Ltd. were later joined as petitioners, but in January 2020 the PTAB terminated their involvement in the proceeding. A hearing on Mylan’s petition was held in November 2019 and on February 5, 2020, the PTAB issued a final written decision upholding the patentability of the ‘514 Patent. Hatch-Waxman Act Litigation relating to TECFIDERA Orange-Book Listed Patents In 2017, 2018 and 2019 we filed patent infringement proceedings relating to TECFIDERA Orange-Book listed patents pursuant to the Drug Price Competition and Patent Term Restoration Act of 1984, commonly known as the Hatch-Waxman Act, against Accord Healthcare Inc., Alkem Laboratories Ltd., Amneal Pharmaceuticals LLC, Aurobindo Pharma U.S.A., Inc., Cipla Limited, Glenmark Pharmaceuticals Ltd., Graviti Pharmaceuticals Pvt. Ltd., Hetero USA, Inc., Lupin Atlantis Holdings SA, Macleods Pharmaceuticals, Ltd., MSN Laboratories Pvt. Ltd., Pharmathen S.A., Prinston Pharmaceutical Inc., Sandoz Inc., Sawai USA, Inc., Shipla Medicare Limited, Slayback Pharma LLC, Torrent Pharmaceuticals Ltd., TWi Pharmaceuticals, Inc., Windlas Healthcare Pvt. Ltd. and Zydus Pharmaceuticals (USA) Inc. (the Delaware Defendants) in the U.S. District Court for the District of Delaware (the Delaware Court) and against Mylan in the U.S. District Court for the Northern District of West Virginia. The litigation against Aurobindo Pharma U.S.A., Inc., Glenmark Pharmaceuticals Ltd. and Sawai USA was dismissed in the fourth quarter of 2019. A trial against the remaining Delaware Defendants was held in the Delaware Court in December 2019 and we are awaiting a decision. A trial is ongoing in the West Virginia action against Mylan. We have entered into settlement agreements with some of the Delaware Defendants and we now anticipate market entry of a generic product equivalent to TECFIDERA before the ‘514 Patent expires in February 2028. In December 2018 we filed an action under the Hatch-Waxman Act against Banner Life Sciences LLC (Banner) for infringement of our U.S. Patent No. 7,619,001 (the ‘001 patent) expiring on June 20, 2020, and claiming treatment of MS with dimethyl fumarate or methyl hydrogen fumarate or a combination thereof. In January 2020 the Delaware Court entered judgment that Banner’s drug product does not infringe the ‘001 patent. We have appealed the decision. European Patent Office Oppositions In 2016 the EPO revoked our European patent number 2 137 537 (the '537 Patent), which covers the treatment of MS with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label. We have appealed to the Technical Boards of Appeal of the EPO and a hearing has been set for March 2020. In March 2018 the EPO revoked Forward Pharma’s European Patent No. 2 801 355, which expires in October 2025. Forward Pharma has filed an appeal to the Technical Boards of Appeal of the EPO and a hearing has been set for June 2020. For additional information regarding this matter, please read Note 6, Intangible Assets and Goodwill, to these consolidated financial statements. TYSABRI Patent Revocation Matters In November 2017 Bioeq GMBH, affiliated with the Polpharma Group, brought an action in the Polish Patent Office seeking to revoke Polish Patent Number 215263 (the Polish '263 Patent), corresponding to our European Patent Number 1 485 127 (the E.U. '127 Patent) and covering administration of natalizumab (TYSABRI) to treat MS. The Polish '263 Patent expires in February 2023. No hearing on the merits has been set in this matter. Swiss Pharma International AG, also affiliated with the Polpharma Group, filed actions in the District Court of the Hague, Netherlands (January 2016), the German Patents Court (March 2016) and the Commercial Court of Rome (November 2017) seeking to invalidate the Dutch, German and Italian counterparts, respectively, of the E.U. '127 Patent, which also cover administration of natalizumab (TYSABRI) to treat MS and expire in February 2023. The Dutch and German counterparts were ruled invalid. The decision in the Dutch action was affirmed on appeal and a hearing has been set for July 2020 in our appeal in the German action. No date for a hearing on the merits has been set in the Italian action. '755 Patent Litigation In May 2010 Biogen MA Inc. (formerly Biogen Idec MA Inc.) filed a complaint in the U.S. District Court for the District of New Jersey alleging infringement by Bayer Healthcare Pharmaceuticals Inc. (Bayer) (manufacturer, marketer and seller of BETASERON and manufacturer of EXTAVIA), EMD Serono, Inc. (EMD Serono) (manufacturer, marketer and seller of REBIF), Pfizer (co-marketer of REBIF) and Novartis Pharmaceuticals Corp. (Novartis) (marketer and seller of EXTAVIA) of our U.S. Patent No. 7,588,755 ('755 Patent), which claims the use of interferon beta for immunomodulation or treating a viral condition, viral disease, cancers or tumors. The complaint seeks monetary damages, including lost profits and royalties. Bayer, Pfizer, Novartis and EMD Serono all filed counterclaims seeking declaratory judgments of patent invalidity and non-infringement and seeking monetary relief in the form of costs and attorneys' fees. Bayer had previously filed a complaint against us in the same court, on May 27, 2010, seeking a declaratory judgment that it does not infringe the '755 Patent and that the '755 Patent is invalid, and seeking monetary relief in the form of attorneys' fees, costs and expenses. In September 2018 the trial court entered judgment against EMD Serono and Pfizer that the '755 Patent is infringed and valid and ordered a new trial on damages. EMD Serono and Pfizer filed an appeal in the U.S. Court of Appeals for the Federal Circuit and oral argument is scheduled for March 2020. The trial court has not yet scheduled the new damages trial or a trial against Bayer and Novartis. Government Matters We have learned that state and U.S. governmental authorities are investigating our sales and promotional practices and have received related subpoenas. We are cooperating with the investigation. We have received subpoenas and other requests from the U.S. government for documents and information relating to our relationship with non-profit organizations that assist patients taking drugs sold by Biogen and the government has challenged some of our contributions to these organizations. We are cooperating with the investigation and have participated in preliminary discussions with the government regarding potential resolution of aspects of the matter. We have accrued the amount of our best estimate of the minimum probable loss in this matter. Tax Matter In the second quarter of 2018 the State Treasury of Goias, Brazil issued tax assessments for the period 2013 through February 2018 relating to tax on the circulation of goods and totaling approximately $70.0 million including interest and penalties. We dispute the assessments and have filed defenses with the Administrative Court of Appeals for the State of Goias, which are pending. We have not formed an opinion that an unfavorable outcome of the dispute is either probable or remote. 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.

Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income attributable to Biogen Idec Inc	$ 1,439.7	$ 1,545.9	$ 1,494.1	$ 1,408.8	$ 946.8	$ 1,444.4	$ 866.6	$ 1,172.9	$ 5,888.5	$ 4,430.7	$ 2,539.1
Denominator:
Weighted average number of common shares outstanding	177.8	184.0	190.3	196.6	199.8	201.4	207.1	211.4	187.1	204.9	212.6
Effect of dilutive securities:
Dilutive potential common shares									0.3	0.4	0.4
Shares used in calculating diluted earnings per share	178.2	184.2	190.4	197.0	200.3	201.9	207.3	211.7	187.4	205.3	213.0
Earnings per share (Textual)
Repurchase of common stock									23.6	14.8	3.7
Stock options and employee stock purchase plan
Effect of dilutive securities:
Stock options and employee stock purchase plan									0.0	0.0	0.1
Time-vested restricted stock units
Effect of dilutive securities:
Stock options and employee stock purchase plan									0.2	0.3	0.2
Market stock units
Effect of dilutive securities:
Stock options and employee stock purchase plan									0.1	0.1	0.1
Performance stock units settled in stock
Effect of dilutive securities:
Stock options and employee stock purchase plan									0.0	0.0	0.0

Employee Benefit Plans (Details 1) - USD ($) $ in Millions	12 Months Ended
Employee Benefit Plans (Details 1) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
GERMANY
Employee Benefit Plans (Textual) [Abstract]
Employee Benefit Plan obligations	$ 59.6	$ 45.3
Periodic pension cost	5.1	5.3	$ 5.2
GERMANY \| Other income (expense)
Employee Benefit Plans (Textual) [Abstract]
Periodic pension cost	$ 1.4	$ 1.5	1.4
SWITZERLAND
Employee Benefit Plans (Textual) [Abstract]
Percentage of minimum investment return	1.00%	1.00%
Unfunded net pension	$ 42.9	$ 48.6
Employee Benefit Plan obligations	127.1	93.1
Pension Cost (Reversal of Cost)	14.7	14.8	12.3
SWITZERLAND \| Other income (expense)
Employee Benefit Plans (Textual) [Abstract]
Pension Cost (Reversal of Cost)	$ 1.2	$ 1.3	$ 1.1

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 5,888.5	$ 4,474.0	$ 2,670.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation, amortization and impairments	680.6	1,016.6	1,081.0
Acquired in-process research and development	0.0	112.5	120.0
Share-based compensation	182.3	157.5	128.0
Deferred income taxes	67.1	108.3	91.7
(Gain) loss on fair value remeasurement of contingent consideration	(63.7)	(12.3)	62.7
Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, Attributable to Parent, before Income Tax	55.3	0.0	0.0
Other	69.2	(69.1)	162.1
Changes in operating assets and liabilities, net:
Accounts receivable	68.8	(205.2)	(435.6)
Due from anti-CD20 therapeutic programs	(63.3)	5.7	(232.0)
Inventory	(19.2)	(52.1)	(94.5)
Accrued expenses and other current liabilities	240.2	465.5	(227.4)
Income tax assets and liabilities	16.1	321.7	1,303.9
Other liabilities	(43.3)	(135.4)	(79.0)
Net cash flows provided by operating activities	7,078.6	6,187.7	4,551.0
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	6,007.0	9,173.7	5,565.9
Purchases of marketable securities	(5,252.6)	(7,694.8)	(5,355.2)
Contingent consideration related to Fumapharm AG acquisition	(300.0)	(1,500.0)	(1,200.0)
Payments to Acquire Businesses, Net of Cash Acquired	(744.4)	0.0	0.0
Proceeds from Sale of Property, Plant, and Equipment	923.7	0.0	0.0
Payments to Acquire in Process Research and Development	0.0	(112.5)	(120.0)
Purchases of property, plant and equipment	(514.5)	(770.6)	(867.4)
Acquisitions of intangible assets	(155.0)	(3.0)	(975.4)
Payments to Acquire Other Investments	0.0	(462.9)	0.0
Payments to increase investment in Samsung Bioepis	0.0	(676.6)	0.0
Proceeds from Sale of Available-for-sale Securities, Equity	479.3	0.0	0.0
Other	27.0	0.4	(11.0)
Net cash flows provided by (used in) investing activities	470.5	(2,046.3)	(2,963.1)
Cash flows from financing activities:
Purchases of treasury stock	(5,868.3)	(4,352.6)	(1,365.4)
Net contribution (distribution) to noncontrolling interests	4.3	(36.4)	(134.1)
Repayments of borrowings	0.0	(3.2)	(560.9)
Net cash contribution to Bioverativ, Inc.	0.0	0.0	(302.7)
Contingent consideration payments	0.0	(58.2)	(3.0)
Other	3.6	(21.6)	(13.9)
Net cash flows used in financing activities	(5,860.4)	(4,472.0)	(2,380.0)
Net increase (decrease) in cash and cash equivalents	1,688.7	(330.6)	(792.1)
Effect of exchange rate changes on cash and cash equivalents	0.4	(18.6)	39.4
Cash and cash equivalents, beginning of the year	1,224.6	1,573.8	2,326.5
Cash and cash equivalents, end of the year	$ 2,913.7	$ 1,224.6	$ 1,573.8

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of assets and liabilities recorded at fair value



As of December 31, 2019 (In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	2,541.1	$	—	$	2,541.1	$	—
Marketable debt securities:
Corporate debt securities	1,695.1		—		1,695.1		—
Government securities	1,013.9		—		1,013.9		—
Mortgage and other asset backed securities	261.3		—		261.3		—
Marketable equity securities	337.5		7.9		329.6		—
Derivative contracts	43.8		—		43.8		—
Plan assets for deferred compensation	27.7		—		27.7		—
Total	$	5,920.4	$	7.9	$	5,912.5	$	—
Liabilities:
Derivative contracts	$	8.3	$	—	$	8.3	$	—
Contingent consideration obligations	346.1		—		—		346.1
Total	$	354.4	$	—	$	8.3	$	346.1



As of December 31, 2018 (In millions)	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	705.5	$	—	$	705.5	$	—
Marketable debt securities:
Corporate debt securities	2,459.2		—		2,459.2		—
Government securities	969.6		—		969.6		—
Mortgage and other asset backed securities	260.5		—		260.5		—
Marketable equity securities	615.4		51.7		563.7		—
Derivative contracts	66.9		—		66.9		—
Plan assets for deferred compensation	25.4		—		25.4		—
Total	$	5,102.5	$	51.7	$	5,050.8	$	—
Liabilities:
Derivative contracts	$	24.6	$	—	$	24.6	$	—
Contingent consideration obligations	409.8		—		—		409.8
Total	$	434.4	$	—	$	24.6	$	409.8

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:



	As of December 31,
(In millions)	2019		2018
2.900% Senior Notes due September 15, 2020	$	1,509.6	$	1,489.5
3.625% Senior Notes due September 15, 2022	1,038.9		1,000.4
4.050% Senior Notes due September 15, 2025	1,897.2		1,745.1
5.200% Senior Notes due September 15, 2045	2,107.9		1,802.6
Total	$	6,553.6	$	6,037.6

Fair value of contingent consideration obligations

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



	As of December 31,
(In millions)	2019			2018
Fair value, beginning of year	$	409.8		$	523.6
Changes in fair value	(63.7		)	(12.3		)
Payments and other	—			(101.5		)
Fair value, end of year	$	346.1		$	409.8

Share-Based Payments (Details Textual)
$ / shares in Units, $ in Millions

12 Months Ended

Dec. 31, 2019

USD ($)

Plan

Increment

$ / shares

Dec. 31, 2018

USD ($)

$ / shares

Dec. 31, 2017

USD ($)

$ / shares

Dec. 31, 2013

Increment

Jun. 30, 2017

Share-based Compensation Arrangement by Share-based Payment Award

Shares issued under ESPP

6,200,000

Share-Based Payments (Textual)

Unrecognized compensation cost related to unvested share-based compensation | $

$ 210.4

Weighted-average period to recognize the cost of unvested awards

1 year 10 months 24 days

Number of share-based compensation plans pursuant to which awards are currently being made | Plan

Number of shares granted under stock options

Total intrinsic value of options exercised | $

$ 4.2

$ 4.0

$ 3.4

Aggregate intrinsic values of options outstanding | $

$ 2.9

Weighted average remaining contractual term for options outstanding

2 months 12 days

Market stock units

Share-based Compensation Arrangement by Share-based Payment Award

Number of equal annual increments | Increment

Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)

0.00%

Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)

200.00%

150.00%

Number of shares granted

^[1]

147,000

Number of days for calculation of average closing stock price

30 days

Total fair value of vested awards | $

$ 32.5

$ 26.9

$ 31.4

Weighted average grant date fair value | $ / shares

$ 378.08

^[1]

$ 378.85

$ 382.59

Cash settled performance units

Share-based Compensation Arrangement by Share-based Payment Award

Number of equal annual increments | Increment

Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)

0.00%

Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)

200.00%

Number of shares granted

Number of days for calculation of average closing stock price

30 days

Cash in settlement of CSPS awards upon vesting | $

$ 10.6

$ 15.1

$ 16.6

Performance units

Share-based Compensation Arrangement by Share-based Payment Award

Number of equal annual increments | Increment

Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)

0.00%

Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)

200.00%

Number of shares granted

Number of days for calculation of average closing stock price

30 days

Cash in settlement of CSPS awards upon vesting | $

$ 10.4

$ 17.0

11.5

Performance stock units settled in stock

Share-based Compensation Arrangement by Share-based Payment Award

Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)

0.00%

Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)

200.00%

Number of shares granted

77,000,000

Weighted average grant date fair value | $ / shares

^[1]

$ 316.28

Performance stock units settled in cash

Share-based Compensation Arrangement by Share-based Payment Award

Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)

0.00%

Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)

200.00%

Number of shares granted

63,000,000

Number of days for calculation of average closing stock price

30 days

Time-vested restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award

Number of shares granted

^[2]

602,000

Total fair value of vested awards | $

$ 131.5

$ 111.7

$ 100.0

Weighted average grant date fair value | $ / shares

$ 304.44

^[2]

$ 316.32

$ 293.41

Director | Time-vested restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award

Number of shares granted

^[2]

15,000

Directors Plan

Share-based Compensation Arrangement by Share-based Payment Award

Total number of shares of common stock for issuance

1,600,000

Ratio of total number of shares reserved under the plan

1.5-to-1

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-to-1

Omnibus Plan number of shares authorized

8,000,000.0

[1]

[2]

RSUs granted in 2019 primarily represent RSUs granted in conjunction with our annual awards made in February 2019 and awards made in conjunction with the hiring of new employees. RSUs granted in 2019 also include approximately 15,000 RSUs granted to our Board of Directors.

Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data (Unaudited)



(In millions, except per share amounts)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Total Year
2019
Product revenues, net	$	2,680.0	$	2,880.3	$	2,894.7	$	2,924.8	$	11,379.8
Revenues from anti-CD20 therapeutic programs	$	517.4	$	576.4	$	595.8	$	600.8	$	2,290.4
Other revenues	$	292.4	$	160.0	$	109.6	$	145.7	$	707.7
Total revenues	$	3,489.8	$	3,616.7	$	3,600.1	$	3,671.3	$	14,377.9
Gross profit ⁽¹⁾	$	2,887.8	$	3,140.4	$	3,170.1	$	3,224.2	$	12,422.5
Net income ^(a)	$	1,408.8	$	1,494.1	$	1,545.9	$	1,439.7	$	5,888.5
Net income attributable to Biogen Inc. ^(a)	$	1,408.8	$	1,494.1	$	1,545.9	$	1,439.7	$	5,888.5
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$	7.17	$	7.85	$	8.40	$	8.10	$	31.47
Diluted earnings per share attributable to Biogen Inc.	$	7.15	$	7.85	$	8.39	$	8.08	$	31.42
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	196.6		190.3		184.0		177.8		187.1
Diluted earnings per share attributable to Biogen Inc.	197.0		190.4		184.2		178.2		187.4



(In millions, except per share amounts)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Total Year
2018
Product revenues, net	$	2,523.5	$	2,757.5	$	2,780.1	$	2,825.7	$	10,886.8
Revenues from anti-CD20 therapeutic programs	$	443.2	$	490.4	$	511.7	$	534.9	$	1,980.2
Other revenues	$	164.4	$	108.6	$	147.2	$	165.7	$	585.9
Total revenues	$	3,131.1	$	3,356.5	$	3,439.0	$	3,526.3	$	13,452.9
Gross profit ⁽¹⁾	$	2,685.1	$	2,935.5	$	2,978.2	$	3,037.8	$	11,636.6
Net income ^(b)	$	1,171.2	$	915.0	$	1,442.9	$	944.9	$	4,474.0
Net income attributable to Biogen Inc. ^(b)	$	1,172.9	$	866.6	$	1,444.4	$	946.8	$	4,430.7
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$	5.55	$	4.18	$	7.17	$	4.74	$	21.63
Diluted earnings per share attributable to Biogen Inc.	$	5.54	$	4.18	$	7.15	$	4.73	$	21.58
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	211.4		207.1		201.4		199.8		204.9
Diluted earnings per share attributable to Biogen Inc.	211.7		207.3		201.9		200.3		205.3

(1) Gross profit is calculated as total revenues less cost of sales, excluding amortization and impairment of acquired intangible assets.


(a)	Net income and net income attributable to Biogen Inc. for 2019 include:


•	Pre-tax gains (losses) related to changes in the fair value of our strategic investments of $376.1 million, ($174.2) million, ($4.6) million and $2.8 million for the first, second, third and fourth quarters, respectively.


•	Impairment charges related to certain intangible assets of $215.9 million in the third quarter. For additional information, please read Note 6, Intangible Assets and Goodwill, to these consolidated financial statements.

•


•	A payment of $45.0 million to Ionis in the fourth quarter, as we exercised our option to obtain a worldwide, exclusive, royalty-bearing license from Ionis to develop and commercialize BIIB080. For additional information, please read, Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

•


(b)	Net income and net income attributable to Biogen Inc. for 2018 include:


•	Pre-tax (losses) gains related to changes in the fair value of our strategic investments of $(6.4) million, $5.4 million, $141.2 million and $(12.2) million for the first, second, third and fourth quarters, respectively.


•	Pre-tax charges to acquired IPR&D of $10.0 million, $75.0 million and $27.5 million for the first, second and third quarters, respectively, for upfront payments made upon closing of asset purchase transactions. For additional information, please read Note 2, Acquisitions, to these consolidated financial statements.


•	Pre-tax research and development expenses for the second quarter of $486.2 million related to the 2018 Ionis Agreement. For additional information, please read, Note 18, Collaborative and Other Relationships, to these consolidated financial statements.

•


•	Impairment charges related to certain intangible assets of $189.3 million and $176.8 million in the third and fourth quarters, respectively. For additional information, please read Note 6, Intangible Assets and Goodwill, to these consolidated financial statements.


•	Losses (gains) related to the adjustments to the fair values of our contingent consideration obligations of $(5.6) million, $1.9 million, $(87.9) million and $79.3 million for the first, second, third and fourth quarters,

respectively. For additional information, please read Note 7, Fair Value Measurements, to these consolidated financial statements.


•	Net increase to income tax expense of $135.8 million for the fourth quarter reflecting the impact of electing to record deferred taxes on GILTI. For additional information, please read Note 16, Income Taxes, to these consolidated financial statements.

•

Share-Based Payments (Details 7) - Performance units	12 Months Ended
Share-Based Payments (Details 7) - Performance units	Dec. 31, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award
Beginning Balance, Unvested, Shares	48,000,000
Shares, Granted	0
Shares, Vested	(33,000,000)
Shares, Forfeited	(4,000,000)
Ending Balance, Unvested, Shares	11,000,000

Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Land	$ 118.1	$ 144.5
Buildings	835.0	1,282.8
Leasehold improvements	99.5	94.4
Machinery and equipment	844.5	1,258.1
Computer software and hardware	798.4	798.7
Furniture and fixtures	58.3	61.6
Construction in progress	2,084.4	1,758.5
Total cost	4,838.2	5,398.6
Less: accumulated depreciation	(1,590.9)	(1,797.4)
Total property, plant and equipment, net	$ 3,247.3	$ 3,601.2

Collaborative and Other Relationships (Details Textual) shares in Millions, $ in Millions, ₩ in Billions	1 Months Ended	3 Months Ended													9 Months Ended	12 Months Ended
	Feb. 29, 2012 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 KRW (₩)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2013	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2019 KRW (₩)	Dec. 31, 2018 KRW (₩)	Nov. 07, 2018 USD ($)	Jun. 05, 2018 USD ($) shares	Sep. 30, 2017	Mar. 31, 2016	Dec. 31, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Collaborative and Other Relationships (Textual)
Research and development																$ 2,280.6	$ 2,597.2	$ 2,253.6
Product Revenues		$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3		$ 3,439.0	$ 3,356.5	$ 3,131.1						14,377.9	13,452.9	12,273.9
Cost of Sales																1,955.4	1,816.3	1,630.0
Collaboration profit (loss) sharing																241.6	185.0	112.3
Potential future milestone payments commitment, approximately		6,800.0														6,800.0
Prepaid research and development		1,252.8				1,690.6									$ 1,690.6	1,252.8	1,690.6
Payments to increase investment in Samsung Bioepis																0.0	676.6	0.0
Equity in loss of investee, net of tax																(79.4)	0.0	0.0
Ionis Pharmaceuticals
Collaborative and Other Relationships (Textual)
Expected additional milestone payments when certain sales threshold is met		800.0														800.0
Research and development									324.1							30.0			$ 10.0
Estimated additional payments upon achievement of development and commercial milestones																260.0
Net change in acquired and in-licensed rights and patents																		150.0
License Fee																70.0
Expected License Fee And Regulatory Milestone Payments		130.0														130.0
Upfront payment for collaboration agreement																							$ 375.0			$ 30.0
Investment in common stock, shares purchased \| shares																							11.5
Upfront And Milestone Payments Made To Collaborative Partner											$ 25.0
Research and development expense asset acquired		45.0							$ 486.2
Additional milestone payment		155.0														155.0										$ 10.0
Term of collaboration agreement									10					six
Total payment to enter collaboration agreement																							$ 1,000.0
Prepaid research and discovery services									$ 50.9
Purchase of common stock																							625.0
Premium on purchase of common stock																							162.1
Investment in common stock, value																							$ 462.9
Ionis Pharmaceuticals \| Minimum
Collaborative and Other Relationships (Textual)
Estimated additional payments upon achievement of development and commercial milestones																125.0
Ionis Pharmaceuticals \| Maximum
Collaborative and Other Relationships (Textual)
Estimated additional payments upon achievement of development and commercial milestones																270.0
Eisai
Collaborative and Other Relationships (Textual)
Biogen's share of expense reflected within our consolidation statements of income																174.3	116.0	74.3
BAN2401 and Elenbecestat R&D expense incurred by collaboration																$ 348.7	232.0	146.2
Percentage of future development costs related to Eisai															15.00%	45.00%
Loss on Contract Termination			$ 48.0		45.0
Alkermes
Collaborative and Other Relationships (Textual)
Research and development											50.0					$ 53.5	68.7	80.3
Upfront And Milestone Payments Made To Collaborative Partner											$ 28.0
Potential future milestone payments commitment, approximately		155.0														155.0
Bristol-Myers Squibb
Collaborative and Other Relationships (Textual)
Research and development												$ 300.0				144.0	97.0
Additional milestone payment		360.0														360.0
iPerian
Collaborative and Other Relationships (Textual)
Additional milestone payment		370.0														370.0
Developmental Milestone Payment												$ 60.0
Acorda
Collaborative and Other Relationships (Textual)
Biogen's share of expense reflected within our consolidation statements of income																42.0	36.5	34.0
Expected additional milestone payments when certain sales threshold is met		15.0														15.0
Foreign sales required to trigger milestone																$ 100.0
AbbVie
Collaborative and Other Relationships (Textual)
Biogen share of co-promotion profits or losses																50.00%
Skyhawk Therapeutics
Collaborative and Other Relationships (Textual)
Upfront And Milestone Payments Made To Collaborative Partner		15.0			74.0
Research and development expense asset acquired		8.0			38.5
Additional milestone payment		2,400.0														$ 2,400.0
Prepaid research and discovery services		7.0			$ 35.5											7.0
Other research and discovery
Collaborative and Other Relationships (Textual)
Research and development																30.6	22.0	10.0
Samsung Bioepis
Collaborative and Other Relationships (Textual)
Research and development													$ 46.0
Estimated additional payments upon achievement of development and commercial milestones																210.0
Contract Option Exercise Fee																60.0
Product Revenues																106.2	96.4	42.7
Collaboration profit (loss) sharing																241.6	187.4	$ 111.0
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
Equity Method Investments, Expected Profit Share																50.00%
Due from Related Parties		85.0				116.9									$ 116.9	$ 85.0	116.9
Due to Related Parties		$ 100.0				$ 31.5									$ 31.5	$ 100.0	$ 31.5
RITUXAN
Collaborative and Other Relationships (Textual)
Percentage of Co promotion Operating Profits first fifty million		30.00%														30.00%				30.00%
Until First GAZYVA Threshold Date		39.00%									37.50%					39.00%		37.50%		39.00%					39.00%
Until GAZYVA First Non-CLL FDA Approval		40.00%														40.00%				40.00%
After First Threshold Date and until Second Threshold Date		37.50%				37.50%									37.50%	37.50%	37.50%			37.50%	37.50%			37.50%
GAZYVA
Collaborative and Other Relationships (Textual)
Percentage of Co promotion Operating Profits first fifty million		35.00%									35.00%					35.00%		35.00%		35.00%
Co-promotion operating profit threshold for Rituxan in U S and Canada to determine share of co promotion operating profit prior to amendment		$ 50.0														$ 50.0
Limit of gross sale of GAZYVA to be achieved in preceding 12 months under option one																150.0
Limit of gross sale of GAZYVA to be achieved in any 12 months under option one																150.0
Sales Trigger Gross Sales Threshold																$ 500.0
Until First GAZYVA Threshold Date		39.00%														39.00%				39.00%
After First Threshold Date and until Second Threshold Date		37.50%														37.50%				37.50%
New Anti-CD20 \| Minimum
Collaborative and Other Relationships (Textual)
Future percentage of co-promotion operating profits																30.00%
New Anti-CD20 \| Maximum
Collaborative and Other Relationships (Textual)
Future percentage of co-promotion operating profits																37.50%
OCREVUS
Collaborative and Other Relationships (Textual)
Royalty operating profit threshold for highest royalty rate percentage																$ 900.0
Reduction in royalty rate																50.00%
Period of collaboration agreement																11 years
OCREVUS \| Minimum
Collaborative and Other Relationships (Textual)
Future royalties percentage to be received on sale of ocrelizumab																13.50%
OCREVUS \| Maximum
Collaborative and Other Relationships (Textual)
Future royalties percentage to be received on sale of ocrelizumab																24.00%
ZINBRYTA
Collaborative and Other Relationships (Textual)
Product Revenues																$ 0.0	$ 1.4	$ 52.7
Unrecorded tax benefit																		93.8
ZINBRYTA \| AbbVie
Collaborative and Other Relationships (Textual)
Biogen's share of expense reflected within our consolidation statements of income																0.3	16.2	19.9
SPINRAZA
Collaborative and Other Relationships (Textual)
Product Revenues																2,097.0	1,724.2	883.7
SPINRAZA \| Ionis Pharmaceuticals
Collaborative and Other Relationships (Textual)
Product Revenues																2,097.0	1,724.2	883.7
Cost of Sales																$ 293.0	238.0	112.4
SPINRAZA \| Ionis Pharmaceuticals \| Minimum
Collaborative and Other Relationships (Textual)
Percentage Of Royalties As Per Collaboration																11.00%
SPINRAZA \| Ionis Pharmaceuticals \| Maximum
Collaborative and Other Relationships (Textual)
Percentage Of Royalties As Per Collaboration																15.00%
SOD1 \| Ionis Pharmaceuticals
Collaborative and Other Relationships (Textual)
Research and development																$ 20.0	18.0	12.0
Estimated additional payments upon achievement of development and commercial milestones																55.0
Upfront And Milestone Payments Made To Collaborative Partner						$ 35.0
VUMERITY
Collaborative and Other Relationships (Textual)
Product Revenues																$ 5.5	0.0	0.0
Net change in acquired and in-licensed rights and patents		$ 155.0
VUMERITY \| Alkermes
Collaborative and Other Relationships (Textual)
Percentage Of Royalties As Per Collaboration																15.00%
Biosimilars
Collaborative and Other Relationships (Textual)
Product Revenues																$ 738.3	545.1	379.8
IMRALDI
Collaborative and Other Relationships (Textual)
Product Revenues																184.0	16.7	0.0
Samsung Bioepis
Collaborative and Other Relationships (Textual)
Net change in acquired and in-licensed rights and patents																		75.0
Additional milestone payment						25.0									$ 25.0		25.0
Investments By Third Party In Joint Venture As Per Agreement.	$ 250.0																										₩ 280.5
Joint Venture Owner Ship Percentage By Third Party.	85.00%
Investment in Samsung Bioepis	$ 45.0	$ 580.2				680.6									$ 680.6	$ 580.2	$ 680.6			₩ 670.8	₩ 759.5						₩ 49.5
Samsung Bioepis, ownership percentage	15.00%	49.90%														49.90%				49.90%							15.00%
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																						$ 675.0
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions																$ 79.4
Payments to increase investment in Samsung Bioepis						$ 676.6	₩ 759.5
Samsung Bioepis, ownership percentage before additional purchase transaction						5.00%									5.00%		5.00%				5.00%
Equity in loss of investee, net of tax																1.2
Amortization																(78.2)
Research and development \| AbbVie
Collaborative and Other Relationships (Textual)
BAN2401 and Elenbecestat R&D expense incurred by collaboration																0.6	$ 32.4	39.9
Selling, general and administrative \| Aducanumab [Member] \| Eisai
Collaborative and Other Relationships (Textual)
Biogen's share of expense reflected within our consolidation statements of income																16.2	5.4	0.0
BAN2401 and Elenbecestat expense incurred by the collaboration																$ 32.4	10.7	0.0
U.S \| Eisai
Collaborative and Other Relationships (Textual)
Biogen share of co-promotion profits or losses																55.00%
U.S \| ZINBRYTA
Collaborative and Other Relationships (Textual)
Product Revenues																$ 0.0	0.0	0.0
U.S \| SPINRAZA
Collaborative and Other Relationships (Textual)
Product Revenues																933.4	854.0	657.0
U.S \| VUMERITY
Collaborative and Other Relationships (Textual)
Product Revenues																5.5	0.0	0.0
U.S \| Biosimilars
Collaborative and Other Relationships (Textual)
Product Revenues																0.0	0.0	0.0
U.S \| IMRALDI
Collaborative and Other Relationships (Textual)
Product Revenues																$ 0.0	0.0	0.0
Outside the U.S \| OCREVUS
Collaborative and Other Relationships (Textual)
Future royalties percentage to be received on sale of ocrelizumab																3.00%
European Union \| Eisai
Collaborative and Other Relationships (Textual)
Biogen share of co-promotion profits or losses																68.50%
JAPAN \| Eisai
Collaborative and Other Relationships (Textual)
Biogen share of co-promotion profits or losses																20.00%
AbbVie \| Collaborative Arrangement
Collaborative and Other Relationships (Textual)
Product Revenues																$ 0.0	(8.6)	(16.9)
AbbVie \| U.S \| Collaborative Arrangement
Collaborative and Other Relationships (Textual)
Product Revenues																	$ (8.6)	$ (16.9)
Inventories \| Samsung Bioepis
Collaborative and Other Relationships (Textual)
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																						115.0
Equity method investment basis difference amortization period																1 year 6 months
Completed technology \| Samsung Bioepis
Collaborative and Other Relationships (Textual)
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																						615.0
Equity method investment basis difference amortization period																15 years
In-process research and development \| Samsung Bioepis
Collaborative and Other Relationships (Textual)
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																						170.0
Deferred tax liability \| Samsung Bioepis
Collaborative and Other Relationships (Textual)
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																						$ 225.0
Development Milestones
Collaborative and Other Relationships (Textual)
Potential future milestone payments commitment, approximately		$ 1,200.0														$ 1,200.0
Development Milestones \| Samsung Bioepis
Collaborative and Other Relationships (Textual)
Additional milestone payment		$ 15.0														$ 15.0

Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

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

The notional value of foreign currency forward contracts that were entered into to hedge forecasted revenues and operating expenses is summarized as follows:



	Notional Amount As of December 31,
Foreign Currency: (In millions)	2019		2018
Euro	$	1,892.4	$	1,701.4
British pound sterling	—		215.3
Swiss francs	—		131.4
Japanese yen	—		98.8
Canadian dollar	—		92.2
Total foreign currency forward contracts	$	1,892.4	$	2,239.1

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

The following tables summarize 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	2019			2018			Location	2019		2018
Revenues	$	118.6		$	(42.5	)	Revenues	$	2.9	$	10.8
Operating expenses	$	(3.3	)	$	0.2		Operating expenses	$	0.2	$	(0.1	)



For the Years Ended December 31,
Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions)				Net Gains/(Losses) Recognized Directly into Net Income (in millions)
Location	2017			Location	2017
Revenues	$	(32.5	)	Other income (expense)	$	8.9
Operating expenses	$	0.6		Other income (expense)	$	(0.2	)

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	2019		2018			Location	2019		2018		Location	2019		2018
Gains (losses) on net investment hedge	$	25.3	$	(3.8	)	Gains (losses) on net investment hedge	$	3.3	$	—	Other income (expense)	$	7.0	$	1.5

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:



(In millions)	Balance Sheet Location	Fair Value As of December 31, 2019		Fair Value As of December 31, 2018
Cash Flow Hedging Instruments:
Asset derivative instruments	Other current assets	$	33.8	$	65.8
Liability derivative instruments	Accrued expenses and other	$	2.0	$	6.9
	Other long-term liabilities	$	1.7	$	—
Net Investment Hedging Instruments:
Asset derivative instruments	Other current assets	$	2.0	$	—
Fair Value Hedging Instruments
Liability derivative instruments	Accrued expenses and other	$	2.3	$	—
	Other long-term liabilities	$	—	$	14.5
Other Derivative Instruments:
Asset derivative instruments	Other current assets	$	8.0	$	1.1
Liability derivative instruments	Accrued expenses and other	$	2.4	$	3.2

Financial Instruments (Details Textual 1)	12 Months Ended
Financial Instruments (Details Textual 1)	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments (Textual)
Original maturities of commercial paper and short-term debt securities	less than 90 days
Average maturity of marketable securities, months	14 months	12 months

Equity Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Nonoperating Income (Expense)									$ 83.3	$ 11.0	$ (217.0)
Income tax benefit (expense)									1,158.0	1,425.6	2,458.7
Product Revenues	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	14,377.9	13,452.9	12,273.9
Net income attributable to Biogen Inc.	$ 1,439.7	$ 1,545.9	$ 1,494.1	$ 1,408.8	$ 946.8	$ 1,444.4	$ 866.6	$ 1,172.9	5,888.5	4,430.7	2,539.1
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.									125.6	(47.0)	(44.2)
Unrealized 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]
Nonoperating Income (Expense)									4.5	(8.5)	(19.5)
Income tax benefit (expense)									(0.9)	1.8	6.8
Unrealized 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]
Nonoperating Income (Expense)									0.3	0.3	0.3
Income tax benefit (expense)									(0.6)	0.2	0.1
Product Revenues									118.6	(42.5)	(32.5)
Operating Expenses									(3.3)	(0.2)	(0.6)
Gains (Losses) on Net Investment Hedge \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Nonoperating Income (Expense)									$ 7.0	$ 1.5	$ 0.0

Revenues Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues from anti-cd20 therapeutic programs	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
Genentech
Disaggregation of Revenue [Line Items]
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses									1,542.4	1,431.9	1,316.4
Other revenues from anti-CD20 therapeutic programs									748.0	548.3	242.8
Revenues from anti-cd20 therapeutic programs
Disaggregation of Revenue [Line Items]
Total revenues from anti-cd20 therapeutic programs	$ 600.8	$ 595.8	$ 576.4	$ 517.4	$ 534.9	$ 511.7	$ 490.4	$ 443.2	$ 2,290.4	$ 1,980.2	$ 1,559.2

Share-Based Payments (Details) - USD ($) $ in Millions	12 Months Ended
Share-Based Payments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	$ (191.2)	$ (168.7)		$ 138.1
Subtotal	225.4	181.6	$ 169.7
Capitalized share-based compensation costs	(8.9)	(11.5)	(9.6)
Share-based compensation expense included in total costs and expenses	216.5	170.1	160.1
Income tax effect	(35.7)	(27.5)	(42.8)
Research and development
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	(77.1)	(75.8)	(74.0)
Selling, general and administrative
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	(148.3)	(105.8)	(95.7)
Total share-based compensation expense, net of tax
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	$ (180.8)	$ (142.6)	$ (117.3)

Acquisitions Schedule of separately identifiable assets acquired and liabilities assumed (Tables)

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

Identified assets acquired and liabilities assumed



(In millions)
Cash and cash equivalents	$	107.8
Marketable securities	7.5
In-process research and development intangible assets	700.0
Goodwill	117.5
Deferred tax liability	(81.9		)
Other, net	1.3
Total purchase price	$	852.2

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income before income tax provision and the income tax expense

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



	For the Years Ended December 31,
(In millions)	2019			2018			2017
Income before income taxes (benefit):
Domestic	$	4,725.3		$	3,877.0		$	3,540.4
Foreign	2,400.6			2,022.6			1,588.4
Total	$	7,125.9		$	5,899.6		$	5,128.8
Income tax expense (benefit):
Current:
Federal	$	947.4		$	1,131.8		$	2,201.4
State	59.1			45.5			57.0
Foreign	84.4			140.0			108.6
Total	1,090.9			1,317.3			2,367.0
Deferred:
Federal	$	1,143.9		$	(62.0	)	$	241.0
State	(2.3		)	(7.4		)	9.9
Foreign	(1,074.5		)	177.7			(159.2		)
Total	67.1			108.3			91.7
Total income tax expense	$	1,158.0		$	1,425.6		$	2,458.7

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)	2019			2018
Deferred tax assets:
Tax credits	$	106.6		$	102.8
Inventory, other reserves and accruals	162.0			163.9
Intangibles, net	3,380.0			2,298.6
Net operating loss	130.4			213.1
Share-based compensation	23.8			25.8
Other	103.7			38.9
Valuation allowance	(1.1		)	(20.0		)
Total deferred tax assets	$	3,905.4		$	2,823.1
Deferred tax liabilities:
Purchased intangible assets	$	(350.3	)	$	(232.8	)
GILTI	(1,381.6		)	(544.6		)
Tax credits	(1,617.2		)	(1,425.7		)
Depreciation, amortization and other	(135.0		)	(102.3		)
Total deferred tax liabilities	$	(3,484.1	)	$	(2,305.4	)

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,
	2019		2018		2017
Statutory rate	21.0	%	21.0	%	35.0	%
State taxes	0.8		0.6		0.8
Taxes on foreign earnings	(4.5	)	(1.9	)	(11.1	)
Credits and net operating loss utilization	(1.1	)	(0.9	)	(0.8	)
Purchased intangible assets	0.4		1.2		1.4
Divestiture of Denmark manufacturing operations	1.0		—		—
Internal reorganization of certain intellectual property rights	(2.1	)	—		—
GILTI	1.5		1.6		—
Other permanent items	0.2		0.3		0.7
U.S. tax reform	—		2.1		22.9
Swiss tax reform	(0.8	)	—		—
Manufacturing deduction	—		—		(1.9	)
Impairment of ZINBRYTA related tax assets	—		—		0.9
Other	(0.1	)	0.2		—
Effective tax rate	16.3	%	24.2	%	47.9	%

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:



	For the Years Ended December 31,
(In millions)	2019			2018			2017
Balance at January 1,	$	114.2		$	66.8		$	32.4
Additions based on tax positions related to the current period	5.3			0.5			5.7
Additions for tax positions of prior periods	17.2			58.7			7.3
Reductions for tax positions of prior periods	(10.3		)	(13.6		)	(21.8		)
Statute expirations	(0.1		)	(2.9		)	(1.4		)
Settlement refund (payment)	3.6			4.7			44.6
Balance at December 31,	$	129.9		$	114.2		$	66.8

Revenues by Product (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Revenues by Product (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Product Revenues	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	$ 3,526.3	$ 3,439.0	$ 3,356.5	$ 3,131.1	$ 14,377.9	$ 13,452.9	$ 12,273.9
TECFIDERA
Disaggregation of Revenue [Line Items]
Product Revenues									4,432.7	4,274.1	4,214.0
Interferon
Disaggregation of Revenue [Line Items]
Product Revenues									2,101.8	2,363.0	2,645.8
TYSABRI
Disaggregation of Revenue [Line Items]
Product Revenues									1,892.2	1,864.0	1,973.1
VUMERITY
Disaggregation of Revenue [Line Items]
Product Revenues									5.5	0.0	0.0
FAMPYRA
Disaggregation of Revenue [Line Items]
Product Revenues									97.1	92.7	91.6
ZINBRYTA
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	1.4	52.7
MS Product Revenues
Disaggregation of Revenue [Line Items]
Product Revenues									8,529.3	8,595.2	8,977.2
SPINRAZA
Disaggregation of Revenue [Line Items]
Product Revenues									2,097.0	1,724.2	883.7
BENEPALI
Disaggregation of Revenue [Line Items]
Product Revenues									486.2	485.2	370.8
FLIXABI
Disaggregation of Revenue [Line Items]
Product Revenues									68.1	43.2	9.0
IMRALDI
Disaggregation of Revenue [Line Items]
Product Revenues									184.0	16.7	0.0
Biosimilars
Disaggregation of Revenue [Line Items]
Product Revenues									738.3	545.1	379.8
FUMADERM
Disaggregation of Revenue [Line Items]
Product Revenues									15.2	22.3	39.6
ELOCTATE
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	48.4
ALPROLIX
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	26.0
Hemophilia Products
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	74.4
Product, net
Disaggregation of Revenue [Line Items]
Product Revenues	$ 2,924.8	$ 2,894.7	$ 2,880.3	$ 2,680.0	$ 2,825.7	$ 2,780.1	$ 2,757.5	$ 2,523.5	11,379.8	10,886.8	10,354.7
U.S \| TECFIDERA
Disaggregation of Revenue [Line Items]
Product Revenues									3,306.5	3,253.2	3,294.0
U.S \| Interferon
Disaggregation of Revenue [Line Items]
Product Revenues									1,426.6	1,668.3	1,889.1
U.S \| TYSABRI
Disaggregation of Revenue [Line Items]
Product Revenues									1,041.8	1,025.0	1,113.8
U.S \| VUMERITY
Disaggregation of Revenue [Line Items]
Product Revenues									5.5	0.0	0.0
U.S \| FAMPYRA
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| ZINBRYTA
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| MS Product Revenues
Disaggregation of Revenue [Line Items]
Product Revenues									5,780.4	5,946.5	6,296.9
U.S \| SPINRAZA
Disaggregation of Revenue [Line Items]
Product Revenues									933.4	854.0	657.0
U.S \| BENEPALI
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| FLIXABI
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| IMRALDI
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| Biosimilars
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| FUMADERM
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
U.S \| ELOCTATE
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	42.2
U.S \| ALPROLIX
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	21.0
U.S \| Hemophilia Products
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	63.2
U.S \| Product, net
Disaggregation of Revenue [Line Items]
Product Revenues									6,713.8	6,800.5	7,017.1
Rest of world \| TECFIDERA
Disaggregation of Revenue [Line Items]
Product Revenues									1,126.2	1,020.9	920.0
Rest of world \| Interferon
Disaggregation of Revenue [Line Items]
Product Revenues									675.2	694.7	756.7
Rest of world \| TYSABRI
Disaggregation of Revenue [Line Items]
Product Revenues									850.4	839.0	859.3
Rest of world \| VUMERITY
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	0.0
Rest of world \| FAMPYRA
Disaggregation of Revenue [Line Items]
Product Revenues									97.1	92.7	91.6
Rest of world \| ZINBRYTA
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	1.4	52.7
Rest of world \| MS Product Revenues
Disaggregation of Revenue [Line Items]
Product Revenues									2,748.9	2,648.7	2,680.3
Rest of world \| SPINRAZA
Disaggregation of Revenue [Line Items]
Product Revenues									1,163.6	870.2	226.7
Rest of world \| BENEPALI
Disaggregation of Revenue [Line Items]
Product Revenues									486.2	485.2	370.8
Rest of world \| FLIXABI
Disaggregation of Revenue [Line Items]
Product Revenues									68.1	43.2	9.0
Rest of world \| IMRALDI
Disaggregation of Revenue [Line Items]
Product Revenues									184.0	16.7	0.0
Rest of world \| Biosimilars
Disaggregation of Revenue [Line Items]
Product Revenues									738.3	545.1	379.8
Rest of world \| FUMADERM
Disaggregation of Revenue [Line Items]
Product Revenues									15.2	22.3	39.6
Rest of world \| ELOCTATE
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	6.2
Rest of world \| ALPROLIX
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	5.0
Rest of world \| Hemophilia Products
Disaggregation of Revenue [Line Items]
Product Revenues									0.0	0.0	11.2
Rest of world \| Product, net
Disaggregation of Revenue [Line Items]
Product Revenues									$ 4,666.0	$ 4,086.3	$ 3,337.6

Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income before income taxes (benefit):
Domestic	$ 4,725.3	$ 3,877.0	$ 3,540.4
Foreign	2,400.6	2,022.6	1,588.4
Income before income tax expense and equity in loss of investee, net of tax	7,125.9	5,899.6	5,128.8
Current
Federal	947.4	1,131.8	2,201.4
State	59.1	45.5	57.0
Foreign	84.4	140.0	108.6
Total	1,090.9	1,317.3	2,367.0
Deferred
Federal	1,143.9	(62.0)	241.0
State	(2.3)	(7.4)	9.9
Foreign	(1,074.5)	177.7	(159.2)
Total	67.1	108.3	91.7
Total income tax expense	$ 1,158.0	$ 1,425.6	$ 2,458.7

Divestitures Divestitures	12 Months Ended
Divestitures Divestitures	Dec. 31, 2019
Divestitures [Abstract]
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	Divestiture of Hillerød, Denmark Manufacturing Operations In August 2019 we completed the sale of all of the outstanding shares of our subsidiary that owned our biologics manufacturing operations in Hillerød, Denmark to FUJIFILM Corporation (FUJIFILM). Upon the closing of this transaction, we received approximately $881.9 million in cash, which may be adjusted based on other contractual terms, which are discussed below. We determined that the operations disposed of in this transaction did not meet the criteria to be classified as discontinued operations under the applicable guidance. As part of this transaction, we have provided FUJIFILM with certain minimum batch production commitment guarantees. There is a risk that the minimum contractual batch production commitments will not be met. Based upon current estimates we expect to incur an adverse commitment obligation of approximately $74.0 million associated with such guarantees and have accrued for this obligation. We may adjust this estimate based upon changes in business conditions, which may result in the increase or reduction of this adverse commitment obligation in subsequent periods. We also may be obligated to indemnify FUJIFILM for liabilities that existed relating to certain business activities incurred prior to the closing of this transaction. In addition, we may earn certain contingent payments based on future manufacturing activities at the Hillerød facility. For the disposition of a business, our policy is to recognize contingent consideration when the consideration is realizable. We currently believe the probability of earning these payments is remote and therefore we did not include these contingent payments in our calculation of the fair value of the operations. As part of this transaction, we entered into certain manufacturing services agreements with FUJIFILM pursuant to which FUJIFILM will use the Hillerød facility to produce commercial products for us, such as TYSABRI, as well as other third-party products. In connection with this transaction, we recognized a total net loss of approximately $164.4 million in our consolidated statements of income. This loss included a pre-tax loss of $95.5 million, which was recorded in loss on divestiture of Hillerød, Denmark manufacturing operations. The loss recognized was based on exchange rates and business conditions on the closing date of this transaction, and included costs to sell our Hillerød, Denmark manufacturing operations of approximately $11.2 million and our estimate of the fair value of an adverse commitment of approximately $114.0 million associated with the guarantee of future minimum batch production at the Hillerød facility. The value of this adverse commitment was determined using a probability-weighted estimate of future manufacturing activity. We also recorded a tax expense of $68.9 million related to this transaction. During the fourth quarter of 2019 we recorded a $40.2 million reduction in our estimate of the future minimum batch commitment utilizing our current manufacturing forecast, which reflects the impact of forecasted aducanumab batches, resulting in a reduction in the pre-tax loss on divestiture from $95.5 million to $55.3 million. In addition, we sold to FUJIFILM $41.8 million of raw materials that were remaining at the Hillerød facility on the closing date of this transaction. These materials were sold at cost, which approximates fair value. Our estimate of the fair value of the adverse commitment is a Level 3 measurement and is based on forecasted batch production at the Hillerød facility.

Revenues (Tables)

12 Months Ended

Dec. 31, 2019

Revenue from Contract with Customer [Abstract]

Revenue by product

Revenues by product are summarized as follows:



	For the Years Ended December 31,
	2019						2018						2017
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis (MS):
TECFIDERA	$	3,306.5	$	1,126.2	$	4,432.7	$	3,253.2	$	1,020.9	$	4,274.1	$	3,294.0	$	920.0	$	4,214.0
Interferon*	1,426.6		675.2		2,101.8		1,668.3		694.7		2,363.0		1,889.1		756.7		2,645.8
TYSABRI	1,041.8		850.4		1,892.2		1,025.0		839.0		1,864.0		1,113.8		859.3		1,973.1
VUMERITY	5.5		—		5.5		—		—		—		—		—		—
FAMPYRA	—		97.1		97.1		—		92.7		92.7		—		91.6		91.6
ZINBRYTA	—		—		—		—		1.4		1.4		—		52.7		52.7
Subtotal: MS Product Revenues	5,780.4		2,748.9		8,529.3		5,946.5		2,648.7		8,595.2		6,296.9		2,680.3		8,977.2

Spinal Muscular Atrophy:
SPINRAZA	933.4		1,163.6		2,097.0		854.0		870.2		1,724.2		657.0		226.7		883.7

Biosimilars:
BENEPALI	—		486.2		486.2		—		485.2		485.2		—		370.8		370.8
IMRALDI	—		184.0		184.0		—		16.7		16.7		—		—		—
FLIXABI	—		68.1		68.1		—		43.2		43.2		—		9.0		9.0
Subtotal: Biosimilar product revenues	—		738.3		738.3		—		545.1		545.1		—		379.8		379.8

Other:
FUMADERM	—		15.2		15.2		—		22.3		22.3		—		39.6		39.6

Hemophilia:
ELOCTATE	—		—		—		—		—		—		42.2		6.2		48.4
ALPROLIX	—		—		—		—		—		—		21.0		5.0		26.0
Subtotal: Hemophilia product revenues	—		—		—		—		—		—		63.2		11.2		74.4

Total product revenues	$	6,713.8	$	4,666.0	$	11,379.8	$	6,800.5	$	4,086.3	$	10,886.8	$	7,017.1	$	3,337.6	$	10,354.7

*Interferon includes AVONEX and PLEGRIDY.

Analysis of change in reserves

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



(In millions)	Discounts			Contractual Adjustments			Returns			Total
2019
Beginning balance	$	127.8		$	888.8		$	34.7		$	1,051.3
Current provisions relating to sales in current year	666.2			3,011.5			20.9			3,698.6
Adjustments relating to prior years	0.3			(54.1		)	5.5			(48.3		)
Payments/returns relating to sales in current year	(535.5		)	(2,242.9		)	(0.2		)	(2,778.6		)
Payments/returns relating to sales in prior years	(127.7		)	(576.0		)	(20.4		)	(724.1		)
Ending balance	$	131.1		$	1,027.3		$	40.5		$	1,198.9



(In millions)	Discounts			Contractual Adjustments			Returns			Total
2018
Beginning balance	$	109.6		$	606.0		$	46.0		$	761.6
Current provisions relating to sales in current year	679.3			2,686.7			23.1			3,389.1
Adjustments relating to prior years	(0.3		)	(10.0		)	(1.8		)	(12.1		)
Payments/returns relating to sales in current year	(551.7		)	(1,887.6		)	(1.1		)	(2,440.4		)
Payments/returns relating to sales in prior years	(109.1		)	(506.3		)	(31.5		)	(646.9		)
Ending balance	$	127.8		$	888.8		$	34.7		$	1,051.3



(In millions)	Discounts			Contractual Adjustments			Returns			Total
2017
Beginning balance	$	71.6		$	482.7		$	51.2		$	605.5
Current provisions relating to sales in current year	583.0			2,307.4			26.9			2,917.3
Adjustments relating to prior years	(0.1		)	15.0			(8.9		)	6.0
Payments/returns relating to sales in current year	(475.8		)	(1,756.9		)	(0.1		)	(2,232.8		)
Payments/returns relating to sales in prior years	(69.1		)	(442.2		)	(23.1		)	(534.4		)
Ending balance	$	109.6		$	606.0		$	46.0		$	761.6

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)	2019		2018
Reduction of accounts receivable	$	197.8	$	176.6
Component of accrued expenses and other	1,001.1		874.7
Total revenue-related reserves	$	1,198.9	$	1,051.3

Revenues from anti-CD20 therapeutic programs

Revenues from anti-CD20 therapeutic programs are 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)	2019		2018		2017
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses	$	1,542.4	$	1,431.9	$	1,316.4
Other revenues from anti-CD20 therapeutic programs	748.0		548.3		242.8
Total revenues from anti-CD20 therapeutic programs	$	2,290.4	$	1,980.2	$	1,559.2

Revenues from anti-CD20 therapeutic programs are summarized as follows:



	For the Years Ended December 31,
(In millions)	2019		2018		2017
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses	$	1,542.4	$	1,431.9	$	1,316.4
Other revenues from anti-CD20 therapeutic programs	748.0		548.3		242.8
Total revenues from anti-CD20 therapeutic programs	$	2,290.4	$	1,980.2	$	1,559.2

Other revenues

Other revenues are summarized as follows:



	For the Years Ended December 31,
(In millions)	2019		2018			2017
Revenues from collaborative and other relationships:
(Loss) profit earned under our 50% share of the co-promotion losses on ZINBRYTA in the U.S. with AbbVie Inc.	$	—	$	(8.6	)	$	(16.9	)
Revenues earned under our technical development services and manufacturing service agreements and royalty revenues on biosimilar products with Samsung Bioepis	106.2		96.4			42.7
Revenues earned under manufacturing services agreement on shipments of ELOCTA and ALPROLIX to Swedish Orphan Biovitrum AB (Sobi) and royalties from Sobi on sales of ELOCTA and ALPROLIX	—		—			10.7
Other royalty and corporate revenues:
Royalty	17.0		38.7			69.8
Other corporate	584.5		459.4			253.7
Total other revenues	$	707.7	$	585.9		$	360.0

Inventory (Details Textual) - USD ($) $ in Millions	12 Months Ended
Inventory (Details Textual) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 01, 2019
Inventory [Line Items]
Inventory raw materials sold to FUJIFILM				$ 41.8
Write-downs on excess, obsolete, unmarketable or other inventory	$ 52.2	$ 41.9	$ 76.9
Work-in-process
Inventory [Line Items]
Inventory work-in-process sold to FUJIFILM				$ 14.0
Bioverativ
Inventory [Line Items]
Inventory sold to Bioverativ, cost	$ 184.5

Revenues Reserves for Discounts and Allowances (Details 2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue related reserves for discounts and allowances	$ 1,198.9	$ 1,051.3	$ 761.6	$ 605.5
Accounts Receivable
Revenue related reserves for discounts and allowances	197.8	176.6
Other Current Liabilities
Revenue related reserves for discounts and allowances	$ 1,001.1	$ 874.7

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	May 31, 2018	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Payment to Neurimmune			$ (4.3)	$ 36.4	$ 134.1
Potential Future Milestone Payments Commitment To Third Party Approximately			6,800.0
Investment in Variable Interest Entities (Textual)
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities			22.7	$ 28.7
Neurimmune
Variable Interest Entity [Line Items]
Payment to Neurimmune	$ 50.0	$ 150.0
Additional reduction in royalty rate payable on commercial sales	5.00%
Reduction in royalty rate payable on commercial sales		15.00%
Regulatory Milestones
Variable Interest Entity [Line Items]
Potential Future Milestone Payments Commitment To Third Party Approximately			1,400.0
Regulatory Milestones \| Neurimmune
Variable Interest Entity [Line Items]
Potential Future Milestone Payments Commitment To Third Party Approximately			75.0
Regulatory Approval Milestone \| Neurimmune
Variable Interest Entity [Line Items]
Potential Future Milestone Payments Commitment To Third Party Approximately			$ 100.0

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2019
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans We sponsor various retirement and pension plans. Our estimates of liabilities and expenses 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 $44.8 million, $42.2 million and $42.6 million for the years ended December 31, 2019, 2018 and 2017, 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, 2019 and 2018, totaled approximately $114.6 million and $109.3 million, respectively, and are included in other long-term liabilities in our consolidated balance sheets. The SSP also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement Plan. The Restoration Match and participant contributions vest immediately. Distributions to participants can be either in one lump sum payment or annual installments as elected by the participants. Pension Plans Our retiree benefit plans include defined benefit plans for employees in our affiliates in Switzerland and Germany as well as other insignificant defined benefit plans in certain other countries where we maintain an operating presence. Our Swiss plan is a government-mandated retirement fund that provides employees with a minimum investment return. The minimum investment return is determined annually by the Swiss government and was 1.00% in 2019, 2018 and 2017. 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, 2019 and 2018, the Swiss plan had an unfunded net pension obligation of $42.9 million and $48.6 million, respectively, and plan assets that totaled $127.1 million and $93.1 million, respectively. In 2019, 2018 and 2017 we recognized expense totaling $14.7 million, $14.8 million and $12.3 million, respectively, related to our Swiss plan, of which $1.2 million, $1.3 million and $1.1 million, respectively, was included in other income (expense), net. The obligations under the German plans are unfunded and totaled $59.6 million and $45.3 million as of December 31, 2019 and 2018, respectively. Net periodic pension cost related to the German plans totaled $5.1 million, $5.3 million and $5.2 million for the years ended December 31, 2019, 2018 and 2017, respectively, of which $1.4 million, $1.5 million and $1.4 million, respectively, was included in other income (expense), net.

Income Taxes (Details 1) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Components of deferred tax assets and liabilities
Tax credits	$ 106.6	$ 102.8
Inventory, other reserves, and accruals	162.0	163.9
Intangibles, net	3,380.0	2,298.6
Net operating loss	130.4	213.1
Share-based compensation	23.8	25.8
Deferred tax assets, other	103.7	38.9
Valuation allowance	(1.1)	(20.0)
Total deferred tax assets	3,905.4	2,823.1
Purchased intangible assets	(350.3)	(232.8)
GILTI	(1,381.6)	(544.6)
Deferred Tax Liabilities, Tax Credit Carryforwards	(1,617.2)	(1,425.7)
Depreciation, amortization and other	(135.0)	(102.3)
Total deferred tax liabilities	$ 3,484.1	$ 2,305.4

Inventory

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Inventory

The components of inventory are summarized as follows:



	As of December 31,
(In millions)	2019		2018
Raw materials	$	169.7	$	196.3
Work in process	460.0		606.7
Finished goods	174.5		133.5
Total inventory	$	804.2	$	936.5

Balance Sheet Classification:
Inventory	$	804.2	$	929.9
Investments and other assets	—		6.6
Total inventory	$	804.2	$	936.5

During 2019 we sold to Bioverativ hemophilia-related inventory on hand as of December 31, 2018, with a cost basis totaling $184.5 million pursuant to the terms of the manufacturing and supply agreement with Bioverativ entered into in connection with the spin-off of our hemophilia business.

Long-term inventory, which primarily consists of work in process, is included in investments and other assets in our consolidated balance sheets.

Inventory amounts written down as a result of excess, obsolescence, unmarketability or other reasons are charged to cost of sales, and totaled $52.2 million, $41.9 million and $76.9 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Divestiture of Hillerød, Denmark Manufacturing Operations

In addition, we sold to FUJIFILM approximately $41.8 million of raw materials that were remaining at the Hillerød facility on the closing date of this transaction. These materials were sold at cost, which approximates fair value.

For additional information on the divestiture of our Hillerød, Denmark manufacturing operations, please read Note 3, Divestitures, to these consolidated financial statements.

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

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)	2019			2018
Land	$	118.1		$	144.5
Buildings	835.0			1,282.8
Leasehold improvements	99.5			94.4
Machinery and equipment	844.5			1,258.1
Computer software and hardware	798.4			798.7
Furniture and fixtures	58.3			61.6
Construction in progress	2,084.4			1,758.5
Total cost	4,838.2			5,398.6
Less: accumulated depreciation	(1,590.9		)	(1,797.4		)
Total property, plant and equipment, net	$	3,247.3		$	3,601.2

Indebtedness (Details Textual) - USD ($)		12 Months Ended
Indebtedness (Details Textual) - USD ($)	Jan. 28, 2020	Dec. 31, 2019	Dec. 31, 2015	Dec. 31, 2018
Debt Instrument
Costs associated with the Senior Notes offerings			$ 47,500,000
Redemptions percentage of 2015 notes		100.00%
Redemption percentage for change in control provision on the 2015 Senior Notes		101.00%
Senior unsecured revolving credit facility maximum borrowing capacity			$ 1,000,000,000.0
Term of credit facility			five
Amount outstanding under the credit facility		$ 0
2.90% Senior Notes due 2020
Debt Instrument
Senior Notes aggregate principal amount			$ 1,500,000,000
Interest rate on senior notes		2.90%	2.90%
Redemption percentage par value of senior notes			99.792%
3.625% Senior Notes due 2022
Debt Instrument
Senior Notes aggregate principal amount			$ 1,000,000,000.0
Interest rate on senior notes		3.625%	3.625%
Redemption percentage par value of senior notes			99.92%
4.05% Senior Notes due 2025
Debt Instrument
Senior Notes aggregate principal amount			$ 1,750,000,000
Interest rate on senior notes		4.05%	4.05%
Redemption percentage par value of senior notes			99.764%
5.20% Senior Notes due 2045
Debt Instrument
Senior Notes aggregate principal amount			$ 1,750,000,000
Interest rate on senior notes		5.20%	5.20%
Redemption percentage par value of senior notes			99.294%
Interest rate swap \| 2.90% Senior Notes due 2020
Debt Instrument
Interest rate swap, liability, fair value		$ 2,300,000		$ 14,500,000
Subsequent Event
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity	$ 1,000,000,000.0
Term of credit facility	five

Fair Value Measurements (Details Textual) - USD ($) $ in Millions	1 Months Ended	3 Months Ended										12 Months Ended
	Feb. 28, 2015	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Mar. 31, 2012	Dec. 31, 2010	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Feb. 12, 2015
Business Acquisition, Contingent Consideration [Line Items]
Fair value measurements, changes in valuation techniques												no	0
Payments												$ 0.0	$ 101.5
Loss (gain) on fair value remeasurement of contingent consideration		$ (2.6)	$ 57.8	$ 20.0	$ (11.5)	$ (79.3)	$ 87.9	$ (1.9)	$ 5.6			63.7	12.3	$ (62.7)
Maximum contingent consideration in the form of development and approval milestones		735.0										735.0
Convergence Pharmaceuticals
Business Acquisition, Contingent Consideration [Line Items]
Additions	$ 274.5
Contingent consideration obligations		244.6				246.6						244.6	246.6
Maximum contingent consideration in the form of development and approval milestones		400.0										400.0
In-process research and development																$ 424.6
Stromedix, Inc.
Business Acquisition, Contingent Consideration [Line Items]
Payments													(81.5)
Additions										$ 122.2
Contingent consideration obligations						83.0							83.0
In-process research and development										$ 219.2
Biogen Idec International Neuroscience GmbH
Business Acquisition, Contingent Consideration [Line Items]
Additions											$ 81.2
Contingent consideration obligations		101.5				80.2						101.5	80.2
Maximum contingent consideration in the form of development and approval milestones		$ 335.0										$ 335.0
2.90% Senior Notes due 2020
Business Acquisition, Contingent Consideration [Line Items]
Interest rate on senior notes		2.90%										2.90%			2.90%
3.625% Senior Notes due 2022
Business Acquisition, Contingent Consideration [Line Items]
Interest rate on senior notes		3.625%										3.625%			3.625%
4.05% Senior Notes due 2025
Business Acquisition, Contingent Consideration [Line Items]
Interest rate on senior notes		4.05%										4.05%			4.05%
5.20% Senior Notes due 2045
Business Acquisition, Contingent Consideration [Line Items]
Interest rate on senior notes		5.20%										5.20%			5.20%
Other long-term liabilities
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration obligations		$ 197.7				$ 265.0						$ 197.7	$ 265.0
Accrued expenses and other \| Convergence Pharmaceuticals
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration obligations		$ 148.5										$ 148.5
Discount rate \| Convergence Pharmaceuticals
Business Acquisition, Contingent Consideration [Line Items]
Fair value measurement and measurement inputs, recurring and nonrecurring		2.10%										2.10%
Discount rate \| Biogen Idec International Neuroscience GmbH
Business Acquisition, Contingent Consideration [Line Items]
Fair value measurement and measurement inputs, recurring and nonrecurring		2.30%										2.30%
BG00011
Business Acquisition, Contingent Consideration [Line Items]
Loss (gain) on fair value remeasurement of contingent consideration			$ 61.2

Leases Leases (Details Textual)	Dec. 31, 2019
Minimum
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Lessee, Operating Lease, Renewal Term	1 year
Maximum
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	10 years
Lessee, Operating Lease, Renewal Term	6 years
Sublease \| Minimum
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Sublease \| Maximum
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	9 years

Other Consolidated Financial Statement Detail (Details Textual) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Other Liabilities, Noncurrent	$ 1,389.4		$ 1,348.9	$ 1,389.4
Increase to goodwill			117.5	1,080.1
Accrued construction in progress	125.2		78.0	125.2
Accrued Income Taxes, Noncurrent	791.4		803.3	791.4
Solothurn
Business Acquisition [Line Items]
Accrued construction in progress	100.0		$ 50.0	100.0
TECFIDERA \| Fumapharm AG
Business Acquisition [Line Items]
Increase to goodwill	300.0			1,200.0
TECFIDERA \| Fumapharm AG \| Twenty billion
Business Acquisition [Line Items]
Increase to goodwill	300.0
Cumulative sales level	20,000.0			20,000.0
TECFIDERA \| Fumapharm AG \| Each additional one billion up to twenty billion
Business Acquisition [Line Items]
Cumulative sales level	$ 20,000.0			$ 20,000.0
TECFIDERA \| Fumapharm AG \| Fifteen billion
Business Acquisition [Line Items]
Cumulative sales level		$ 15,000.0
TECFIDERA \| Fumapharm AG \| Sixteen billion
Business Acquisition [Line Items]
Increase to goodwill		600.0
Cumulative sales level		$ 16,000.0

Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash equivalents	$ 2,541.1	$ 705.5
Marketable equity securities	337.5	615.4
Derivative contracts	43.8	66.9
Plan assets for deferred compensation	27.7	25.4
Total	5,920.4	5,102.5
Liabilities:
Derivative contracts	8.3	24.6
Contingent consideration obligations	346.1	409.8	$ 523.6
Total	354.4	434.4
Corporate debt securities
Assets:
Marketable debt securities	1,695.1	2,459.2
Government securities
Assets:
Marketable debt securities	1,013.9	969.6
Mortgage and other asset backed securities
Assets:
Marketable debt securities	261.3	260.5
Quoted Prices in Active Markets (Level 1)
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	7.9	51.7
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	7.9	51.7
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration obligations	0.0	0.0
Total	0.0	0.0
Quoted Prices in Active Markets (Level 1) \| Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) \| Government securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) \| Mortgage and other asset backed securities
Assets:
Marketable debt securities	0.0	0.0
Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	2,541.1	705.5
Marketable equity securities	329.6	563.7
Derivative contracts	43.8	66.9
Plan assets for deferred compensation	27.7	25.4
Total	5,912.5	5,050.8
Liabilities:
Derivative contracts	8.3	24.6
Contingent consideration obligations	0.0	0.0
Total	8.3	24.6
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Assets:
Marketable debt securities	1,695.1	2,459.2
Significant Other Observable Inputs (Level 2) \| Government securities
Assets:
Marketable debt securities	1,013.9	969.6
Significant Other Observable Inputs (Level 2) \| Mortgage and other asset backed securities
Assets:
Marketable debt securities	261.3	260.5
Significant Unobservable Inputs (Level 3)
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	0.0	0.0
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration obligations	346.1	409.8
Total	346.1	409.8
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Government securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) \| Mortgage and other asset backed securities
Assets:
Marketable debt securities	$ 0.0	$ 0.0