Expense incurred by the collaboration
Expense incurred by the collaboration
Expense incurred by the collaboration
Expense incurred by the collaboration
Consolidated Entities [Axis]
Consolidated Entities [Axis]
Net income (loss) attributable to noncontrolling interests, net of tax
Net Income (Loss) Attributable to Noncontrolling Interest
(Gain) loss on fair value remeasurement of contingent consideration
Contingent consideration
Contingent consideration impairment
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings
Intangible assets
Intangible Assets Excluding Goodwill [Table Text Block]
Intangible assets excluding goodwill.
Accrued expenses and other
Schedule of Accrued Liabilities [Table Text Block]
Statistical Measurement [Domain]
Statistical Measurement [Domain]
Research and development expense asset acquired
Research and Development Expense
Changes in operating assets and liabilities, net:
Increase (Decrease) in Operating Capital [Abstract]
Royalties and licensing fees
Accrued Royalties, Current
Gain on derivative used in net investment hedge
Other Comprehensive Income (Loss), Net Investment Hedge, Gain (Loss), Reclassification, before Tax
Award Type [Domain]
Award Type [Domain]
Investment, Name [Domain]
Investment, Name [Domain]
Component of accrued expenses and other
Other Current Liabilities [Member]
Statement of Stockholders' Equity [Abstract]
Statement of Stockholders' Equity [Abstract]
Investments, Debt and Equity Securities [Abstract]
Investments, Debt and Equity Securities [Abstract]
Payments/Returns Relating To Sales in Prior Year
Payments Returns Applied Against Product Revenue Reserves Relating To Prior Year
Payments/ returns applied against product revenue reserves relating to prior year.
Effect of exchange rate changes on cash and cash equivalents
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations
Deferred tax liability
Deferred Income Tax Liabilities, Net
Accounts payable
Accounts Payable, Current
Investment, Name [Axis]
Investment, Name [Axis]
Corporate debt securities
Corporate Debt Securities [Member]
Denali Therapeutics
Denali Therapeutics Inc [Member]
Denali Therapeutics Inc
Statutory rate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
Royalty percentage to be received
Future Royalties Percentage To Be Received On Sale Of Product
Future royalties percentage to be received on sale of product.
Commitments, contingencies and guarantees
Commitments and Contingencies
Construction in progress
Construction in Progress, Gross
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Line Items]
Foreign currency and other adjustments
Restructuring Reserve, Foreign Currency Translation Gain (Loss)
SPINRAZA
SPINRAZA [Member]
SPINRAZA [Member]
Equity
Equity [Text Block]
TYSABRI
TYSABRI product [Member]
TYSABRI product [Member]
Accrued Expenses and Other
Accrued Liabilities, Current [Abstract]
Geographical [Axis]
Geographical [Axis]
2022 Cost Saving Initiative
2022 Cost Saving Initiatives [Member]
2022 Cost Saving Initiatives
Excess and obsolescence charges related to inventory
Inventory Write-down
Collaborative Arrangement and Arrangement Other than Collaborative [Axis]
Collaborative Arrangement and Arrangement Other than Collaborative [Axis]
Centers for Medicare and Medicaid Service
Centers for Medicare and Medicaid Service [Member]
Centers for Medicare and Medicaid Service
Income Taxes
Income Tax Disclosure [Text Block]
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA
Share Of Co Promotion Profits
Share of co promotion profits.
Variable Interest Entity [Line Items]
Variable Interest Entity [Line Items]
Canadian dollar
Canada, Dollars
Customer [Axis]
Customer [Axis]
Current liabilities:
Liabilities, Current [Abstract]
Accumulated impairment losses related to goodwill
Goodwill, Impaired, Accumulated Impairment Loss
Preferred stock, par value $0.001 per share
Preferred Stock, Value, Issued
Business Acquisition [Line Items]
Business Acquisition [Line Items]
Fair Value, Recurring and Nonrecurring [Table]
Fair Value, Recurring and Nonrecurring [Table]
Diluted earnings per share attributable to Biogen Inc.
Earnings Per Share, Diluted
Derivative liability, fair value
Derivative Liability, Subject to Master Netting Arrangement, before Offset
Property, Plant and Equipment [Table]
Property, Plant and Equipment [Table]
Hedging Relationship [Axis]
Hedging Relationship [Axis]
Treasury stock, at cost
Treasury Stock, Value
Accounts receivable, net
Accounts Receivable, after Allowance for Credit Loss, Current
Derivative contracts
Foreign Currency Contracts, Liability, Fair Value Disclosure
International reorganization
Effective Tax Rate Reconciliation, International Reorganization
Effective Tax Rate Reconciliation, International Reorganization
Summary of roll forward of the changes in goodwill
Goodwill [Roll Forward]
Significant Unobservable Inputs (Level 3)
Fair Value, Inputs, Level 3 [Member]
Beginning balance, treasury stock, shares
Ending balance, treasury stock, shares
Treasury Stock, Common, Shares
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Issuance of common stock under stock award plan
Stock Issued During Period, Value, Stock Options Exercised
Trading Symbol
Trading Symbol
Contractual adjustments
Contractual Adjustments [Member]
Contractual adjustments.
Restructuring Plan [Domain]
Restructuring Plan [Domain]
Marketable equity securities
Investments, Fair Value Disclosure
Collaborative Arrangement and Arrangement Other than Collaborative [Table]
Collaborative Arrangement and Arrangement Other than Collaborative [Table]
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Short-term debt securities
Debt Securities [Member]
Net income attributable to Biogen Inc.
Net income attributable to Biogen Inc.
Net Income (Loss)
Completed technology
Out Licensed Patents [Member]
Out-licensed patents.
Total current liabilities
Liabilities, Current
Derivative Contract [Domain]
Derivative Contract [Domain]
Distributor Two
Distributor Two [Member]
Distributor two.
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Abstract]
Adjustments Relating To Prior Years
Adjustments To Product Revenue Reserves Relating To Sales In Prior Years
Adjustments to product revenue reserves relating to sales in prior years.
Percentage of stake in entity
Equity Method Investment, Ownership Percentage Before Additional Purchase Transaction
Equity Method Investment, Ownership Percentage Before Additional Purchase Transaction
Due after one year through five years, amortized cost
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five
Indefinite-lived Intangible Assets, Major Class Name [Domain]
Indefinite-Lived Intangible Assets, Major Class Name [Domain]
Summary of financial assets with maturities of less than 90 days included within cash and cash equivalents
Schedule of Cash and Cash Equivalents [Table Text Block]
Total intangible assets, gross
Intangible Assets, Gross (Excluding Goodwill)
All Currencies [Domain]
All Currencies [Domain]
LIABILITIES AND EQUITY
Liabilities and Equity [Abstract]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets [Line Items]
Market stock units
Market Stock Units [Member]
Market stock units.
Biogen Idec Inc. shareholders' equity
Equity, Attributable to Parent [Abstract]
Gross unrealized losses
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax
Issuance of common stock under award plan, shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period
Mortgage and other asset backed securities Current
Mortgage And Other Asset Backed Securities Current [Member]
Mortgage and other asset backed securities Current.
Basic and diluted earnings per share
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Cost of sales, excluding amortization and impairment of acquired intangible assets
Cost of Goods and Services Sold
Income Tax Contingency [Table]
Income Tax Contingency [Table]
Range of durations of foreign currency forward contracts
Derivative, Remaining Maturity
Gain (loss) on foreign currency derivative instruments not designated as hedging instruments
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments
Reduction in royalty rate
Reduction in royalty rate
Reduction in royalty rate
Neurimmune tax impacts
Effective Tax Rate Reconciliation, NuerImmune Tax Impacts
Effective Tax Rate Reconciliation, NuerImmune Tax Impacts
Foreign exchange contract
Foreign Exchange Contract [Member]
Summary of significant accounting policies
Significant Accounting Policies [Text Block]
Contingent Commercialized Rights, Number Of Products
Contingent Commercialized Rights, Number Of Products
Contingent Commercialized Rights, Number Of Products
Quoted Prices in Active Markets (Level 1)
Fair Value, Inputs, Level 1 [Member]
Share-based compensation expense included in total costs and expenses
Share Based Compensation Expense Included In Costs And Expenses
Share based compensation expense included in costs and expenses.
Sale of Samsung Bioepis
Effective Tax Rate Reconciliation, Sale Of Samsung Bioepis
Effective Tax Rate Reconciliation, Sale Of Samsung Bioepis
Goodwill
Goodwill, beginning of period
Goodwill, end of period
Goodwill
Fair value of post-combination equity compensation
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized
Equity Components [Axis]
Equity Components [Axis]
Financial Instruments [Domain]
Financial Instruments [Domain]
IMRALDI
IMRALDI [Member]
IMRALDI [Member]
Accrued expense and other current liabilities
Increase (Decrease) in Accrued Liabilities
Hedging Relationship [Domain]
Hedging Relationship [Domain]
Short-term certificates of deposit
Certificates of Deposit [Member]
Investment Type [Axis]
Investment Type [Axis]
Disaggregation of Revenue [Abstract]
Disaggregation of Revenue [Abstract]
Purchased intangible assets
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation and Amortization, Percent
Percentage of revenues from major distributors
Entity Wide Percentage Of Revenue From Major Distributors
Entity wide percentage of revenue from major distributors.
Entity Small Business
Entity Small Business
Investment Type Categorization [Domain]
Investments [Domain]
Expected future amortization expense, 2027
Finite-Lived Intangible Asset, Expected Amortization, Year Four
Local Phone Number
Local Phone Number
Accounts receivable
Increase (Decrease) in Accounts Receivable
Forecast
Forecast [Member]
Schedule of Business Acquisitions by Acquisition, Contingent Consideration [Table]
Schedule of Business Acquisitions by Acquisition, Contingent Consideration [Table]
Derivative, Notional Amount
Derivative, Notional Amount
Reduction of accounts receivable
Accounts Receivable [Member]
Selling, general and administrative
Selling, general and administrative
Selling, General and Administrative Expenses [Member]
Investments in Variable Interest Entities [Abstract]
Investments in Variable Interest Entities [Abstract]
Investments In Variable Interest Entities.
Measurement Frequency [Axis]
Measurement Frequency [Axis]
Long-term operating lease liabilities
Operating Lease, Liability, Noncurrent
Summary of contractual maturities: available-for-sale securities
Investments Classified by Contractual Maturity Date [Table Text Block]
Other research and discovery
Other research and discovery [Member]
Other research and discovery [Member]
Accrued expenses and other
Accrued Liabilities [Member]
Depreciation
Depreciation
Debt Instrument, Name [Domain]
Debt Instrument, Name [Domain]
Plan assets for deferred compensation
Plan Assets For Deferred Compensation Fair Value Disclosure
Fair values as of the balance sheet date of all assets of deferred compensation plans.
Reclassification out of Accumulated Other Comprehensive Income [Axis]
Reclassification out of Accumulated Other Comprehensive Income [Axis]
GILTI
Effective Tax Rate Reconciliation, GILTI tax
Effective Tax Rate Reconciliation, GILTI tax
Income Statement Location [Axis]
Income Statement Location [Axis]
Collaborative Arrangement and Arrangement Other than Collaborative [Domain]
Collaborative Arrangement and Arrangement Other than Collaborative [Domain]
Research and development
Research and Development Expense (Excluding Acquired in Process Cost)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Subtotal
Subtotal
Share-Based Payment Arrangement, Expense, after Tax
Current Provisions Relating To Sales In Current Year
Current Provisions To Product Revenue Reserves Relating To Sales In Current Year
Current provisions to product revenue reserves relating to sales in current year.
Fumarate
Fumarate [Member]
Fumarate [Member]
Dilutive potential common shares
Weighted Average Number of Shares Outstanding, Diluted, Adjustment
Foreign Exchange Forward
Foreign Exchange Forward [Member]
3.150% Senior Notes due May 1, 2050
3.15% Senior Notes due May 1, 2050 [Member]
3.15% Senior Notes due May 1, 2050 [Member]
Gain on sale of equity interest in Samsung Bioepis
Gain (Loss) on Sale of Investments
Total revenue
Product revenues
Total revenues from anti-CD20 therapeutic programs
Revenues
BYOOVIZ
BYOOVIZ [Member]
BYOOVIZ
Collaborative Arrangement, Profit (Loss) Sharing Components [Domain]
Collaborative Arrangement, Profit (Loss) Sharing Components [Domain]
Collaborative Arrangement, Profit (Loss) Sharing Components
Product and Service [Domain]
Product and Service [Domain]
Discounts
Reserve for Cash Discounts [Member]
Reserve for Cash Discounts [Member]
Number of wholesalers
Number of Wholesalers
Number of Wholesalers
Inventory
Increase (Decrease) in Inventories
4.050% Senior Notes due 2025
Senior Notes Four Point Zero Five Percent Due Twenty Twenty Five [Member]
Senior Notes Four Point Zero Five Percent Due Twenty Twenty Five [Member]
Research and development
Research and development
Research and Development Expense [Member]
Cash flows from investing activities:
Net Cash Provided by (Used in) Investing Activities [Abstract]
Restructuring reserve, beginning
Restructuring reserve, ending
Restructuring Reserve
Notes payable, fair value
Notes Payable, Fair Value Disclosure
Award Type [Axis]
Award Type [Axis]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Expected profit share percentage
Equity Method Investments, Expected Profit Share
Equity Method Investments, Expected Profit Share
Document Quarterly Report
Document Quarterly Report
Interest expense
Interest Expense
Payable Due To Termination Agreement
Accrued Payment To Termination Agreement
Accrued Payment To Termination Agreement
Fair Value Hierarchy and NAV [Domain]
Fair Value Hierarchy and NAV [Domain]
Other Consolidated Financial Statement Detail
Additional Financial Information Disclosure [Text Block]
Hedging Designation [Axis]
Hedging Designation [Axis]
Expected future amortization expense, 2023 (remaining three months)
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year
Use of estimates
Use of Estimates, Policy [Policy Text Block]
Derivatives [Line Items]
Derivatives, Fair Value [Line Items]
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities.
Marketable debt securities
Debt Securities, Available-for-Sale [Abstract]
Entity File Number
Entity File Number
Ionis, Sangamo, Denali and Sage
Ionis, Sangamo, Denali and Sage [Member]
Ionis, Sangamo, Denali and Sage
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table]
Summary of assets and liabilities recorded at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Divestitures [Abstract]
Divestitures [Abstract]
Divestitures [Abstract]
Discount rates
Measurement Input, Discount Rate [Member]
Gains (losses) on securities available for sale
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member]
Accounts payable
Accounts Payable
Proceeds from maturities and sales
Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale
Entity Shell Company
Entity Shell Company
Equity Method Investment, Amount Sold
Equity Method Investment, Amount Sold
Business Acquisition, Acquiree [Domain]
Business Acquisition, Acquiree [Domain]
Research and development asset [Domain]
Research and development asset [Domain]
Research and development asset [Domain]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment [Line Items]
Net
Finite-Lived Intangible Assets, Net
New accounting pronouncements
New Accounting Pronouncements, Policy [Policy Text Block]
Collaborative Arrangement, Profit (Loss) Sharing Components [Axis]
Collaborative Arrangement, Profit (Loss) Sharing Components [Axis]
Collaborative Arrangement, Profit (Loss) Sharing Components
Percentage of co promotion operating profits first fifty million
Percentage Of Co Promotion Operating Profits First Fifty Million
Percentage of co promotion operating profits first fifty million.
Income tax assets and liabilities
Increase (Decrease) in Income Taxes Payable
Counterparty Name [Domain]
Counterparty Name [Domain]
Schedule of Restructuring and Related Costs [Table]
Schedule of Restructuring and Related Costs [Table]
Cash and cash equivalents
Cash and cash equivalents, beginning of the period
Cash and cash equivalents, end of the period
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents
Asset Class [Axis]
Asset Class [Axis]
Accumulated Amortization
Finite-Lived Intangible Assets, Accumulated Amortization
Facility Location [Domain]
Facility Location [Domain]
-- None. No documentation exists for this element. --
Debt Instrument, Fair Value Disclosure
Debt Instrument, Fair Value Disclosure
Biologics Manufacturing
Biologics Manufacturing [Member]
Biologics Manufacturing
Interest income
Investment Income, Interest
Severance Costs
Severance Costs
Security Exchange Name
Security Exchange Name
Total
Assets, Fair Value Disclosure
Notes payable
Long-Term Debt
Selling, general and administrative
Selling, General and Administrative Expense
Co-promotion profit sharing formula
Co Promotion Profit Sharing Formula [Table Text Block]
Co-promotion profit sharing formula.
Accumulated other comprehensive income (loss)
Accumulated other comprehensive income (loss), net of tax beginning balance
Balance, January 1, 2018
Accumulated other comprehensive income (loss), net of tax ending balance
Accumulated Other Comprehensive Income (Loss), Net of Tax
Swiss franc
Switzerland, Francs
Other comprehensive income (loss), before reclassifications, net of tax
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax
Collaborative and Other Relationships
Collaborative Arrangement Disclosure [Text Block]
Options
Employee Stock Option [Member]
Currency translation adjustments
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Derivative Instruments
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Beginning Balance
Ending Balance
Total Reserves
Revenue-related reserves for discounts and allowances
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount
Derivative contracts
Foreign Currency Contract, Asset, Fair Value Disclosure
Total cost and expense
Costs and Expenses
Other
Proceeds from (Payments for) Other Financing Activities
Maximum
Maximum [Member]
Comprehensive income (loss) attributable to Biogen Inc.
Comprehensive Income (Loss), Net of Tax, Attributable to Parent
Restructuring and Related Costs
Restructuring and Related Costs [Table Text Block]
Cash equivalents
Cash Equivalents, at Carrying Value
Document Type
Document Type
Other revenues from anti-CD20 therapeutic programs
Other revenues from anti-CD20 therapeutic programs
Other revenues from anti-CD20 therapeutic programs consists of revenue on sales of RITUXAN outside the U.S., which consist of our share of pre-tax co-promotion profits in Canada and royalty revenue on sales of Ocrevus.
Reclassification out of Accumulated Other Comprehensive Income [Table]
Reclassification out of Accumulated Other Comprehensive Income [Table]
Facility Type [Domain]
Facility Type [Domain]
Facility Type
Overnight reverse repurchase agreements
Repurchase Agreements [Member]
Entity Address, Address Line One
Entity Address, Address Line One
BENEPALI
BENEPALI [Member]
BENEPALI [Member]
Repurchase of common stock pursuant to the 2020 Share Repurchase Program, at cost
Treasury stock, value, acquired, cost method
Treasury Stock, Value, Acquired, Cost Method
Antidilutive Securities, Name [Domain]
Antidilutive Securities, Name [Domain]
Proceeds from marketable debt securities
Realized Gain (Loss) on Investments [Table Text Block]
Share-based Payments
Share-Based Payment Arrangement [Text Block]
Net increase (decrease) in cash and cash equivalents
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect
Gain on sale of equity interest in Samsung Bioepis(1)
Equity Method Investment, Realized Gain (Loss) on Disposal
Basis of presentation
Basis of Accounting, Policy [Policy Text Block]
Other
Other Noncash Income (Expense)
Purchases of marketable securities
Payments to Acquire Debt Securities, Available-for-Sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Business Acquisition [Axis]
Business Acquisition [Axis]
Gross Unrealized Gains
Equity Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax
Equity Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax
Taxes payable
Taxes Payable, Current
Net losses recognized on the decrease in fair value of equity securities
Equity Securities, FV-NI, Unrealized Loss
Strategic Investments
Strategic Investments [Member]
Strategic investments.
Total reserves included in consolidated balance sheets
Summary Of Product Revenue Reserves Included In Consolidated Balance Sheets [Table Text Block]
Summary of total product revenue reserves included in consolidated balance sheets.
Trademarks and Trade Names
Trademarks and Trade Names [Member]
Inventory
Inventory
Inventory, Net Current and Noncurrent
Inventory, Net Current and Noncurrent
Restructuring charges
Restructuring Charges [Member]
Accrued expense and other
Total accrued expense and other
Other Liabilities, Current
Future Contingent Milestone Types [Domain]
Future Contingent Milestone Types [Domain]
[Domain] for Future Contingent Milestone Types [Axis]
Gain on sale of equity interest in Samsung Bioepis
Gain (Loss) on Disposition of Stock in Subsidiary or Equity Method Investee
Income Statement [Abstract]
Income Statement [Abstract]
Inventory [Line Items]
Inventory [Line Items]
Raw materials
Inventory, Raw Materials, Net of Reserves
Cost and expenses:
Costs and Expenses [Abstract]
Option exercise fee
Contract Option Exercise Fee
Contract Option Exercise Fee
Title of 12(b) Security
Title of 12(b) Security
Restructuring Cost and Reserve [Line Items]
Restructuring Cost and Reserve [Line Items]
Cash equivalents
Cash and Cash Equivalents, Fair Value Disclosure
Payables to divestiture of interest in joint venture
Payables To Divestiture Of Interest In Joint Venture
Payables To Divestiture Of Interest In Joint Venture
Schedule of Restructuring Reserve by Type of Cost
Schedule of Restructuring Reserve by Type of Cost [Table Text Block]
Limit of gross sale of GAZYVA to be achieved in any 12 months under option one
Threshold Of Gross Sales To Be Achieved In Any Twelve Consecutive Months Under Option One
Threshold of gross sales to be achieved in any twelve consecutive months under option one.
Related Party, Type [Domain]
Related Party, Type [Domain]
Cost and Net
Indefinite-lived Intangible Assets (Excluding Goodwill)
Indefinite-Lived Intangible Assets (Excluding Goodwill)
TECFIDERA
TECFIDERA [Member]
TECFIDERA [Member]
Derivative Instruments, Unrealized Gain (Loss)
Derivative Instruments, Unrealized Gain (Loss) [Table Text Block]
Derivative Instruments, Unrealized Gain (Loss)
Numerator:
Net Income (Loss) Attributable to Parent [Abstract]
Other current assets
Other Assets, Current
Class of Stock [Line Items]
Class of Stock [Line Items]
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Abstract]
Share-based Payment Arrangement [Abstract]
Share-Based Payment Arrangement [Abstract]
Entity Tax Identification Number
Entity Tax Identification Number
Investment in Samsung Bioepis
Equity Method Investments
Percentage of future development costs
Percentage Of Future Development Costs
Percentage Of Future Development Costs
OCREVUS
OCREVUS [Member]
OCREVUS
Inventory
Inventory, current
Inventory, Net
Payment Due At First Anniversary
Payment Due At First Anniversary [Member]
Payment Due At First Anniversary
Capitalized share-based compensation costs
Share-Based Payment Arrangement, Amount Capitalized
Statistical Measurement [Axis]
Statistical Measurement [Axis]
Administrative Space
Administrative Space [Member]
Administrative Space
Inventory, noncurrent
Inventory, Noncurrent
Net (distribution) contribution to noncontrolling interest
Proceeds from (Payments to) Noncontrolling Interests
Financial Instrument [Axis]
Financial Instrument [Axis]
Balance Sheet Location [Domain]
Balance Sheet Location [Domain]
Dispositions
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]
Entity Interactive Data Current
Entity Interactive Data Current
Disaggregation of Revenue [Table]
Disaggregation of Revenue [Table]
Derivative Maturity [Axis]
Derivative Maturity [Axis]
Derivative Maturity [Axis]
Summary of activity related to the UCB collaboration
Summary of Activity Related to the UCB Collaboration [Table Text Block]
Summary of Activity Related to the UCB Collaboration
Schedule of Available-for-sale Securities [Table]
Debt Securities, Available-for-Sale [Table]
Gross Unrealized Losses
Equity Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, Before Tax
Equity Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, Before Tax
Purchases of treasury stock
Payments for Repurchase of Common Stock
Product, net
Product [Member]
Entity Common Stock, Shares Outstanding
Entity Common Stock, Shares Outstanding
Retirement of common stock pursuant to the 2020 Share Repurchase Program, at cost
Treasury Stock, Retired, Cost Method, Amount
Japan, Yen
Japan, Yen
Inventory Disclosure [Abstract]
Inventory Disclosure [Abstract]
Parent
Total share-based compensation expense, net of tax
Parent [Member]
Number of square feet
Number of Square Feet
Number of Square Feet
Fair Value Hierarchy and NAV [Axis]
Fair Value Hierarchy and NAV [Axis]
Performance stock units settled in stock
Performance Stock Units Settled in Stock [Member]
Performance Stock Units Settled in Stock [Member]
Interferon
Interferon [Member]
Interferon
Other income (expense), net
Schedule of Other Nonoperating Income (Expense) [Table Text Block]
Retained earnings
Retained Earnings (Accumulated Deficit)
FUMADERM And ADUHELM
FUMADERM And ADUHELM [Member]
FUMADERM And ADUHELM
Corporate debt securities Non-current
Corporate Debt Securities Non Current [Member]
Corporate Debt Securities Non Current.
Samsung Bioepis
Samsung Biosimilar Agreement [Member]
Samsung bio-similar agreement.
Entity Incorporation, State or Country Code
Entity Incorporation, State or Country Code
Current assets:
Assets, Current [Abstract]
Research and development costs, percentage
Research and Development Costs, Percentage
Research and Development Costs, Percentage
Short-term derivative
Short-term derivative [Member]
Short-term derivative [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Acquisition, Contingent Consideration [Line Items]
Entity Address, State or Province
Entity Address, State or Province
Counterparty Name [Axis]
Counterparty Name [Axis]
Summary of fair and carrying value of debt instruments
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block]
Risk-adjusted discount rates
Other Assets, Measurement Input
Other Assets, Measurement Input
Cash flow from operating activities:
Net Cash Provided by (Used in) Operating Activities [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Expected future amortization expense, 2024
Finite-Lived Intangible Asset, Expected Amortization, Year One
Summary of share-based compensation expense associated with each of our share-based compensating programs
Share-Based Payment Arrangement, Cost by Plan [Table Text Block]
Beginning balance, shares
Ending balance, shares
Common Stock, Shares, Outstanding
Unrealized gains (losses) on securities available for sale, net of tax
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax
Unrealized Gain on Derivatives
Unrealized Gain on Derivatives
Unrealized Gain on Derivatives
(Gain) loss on strategic investments
Increase (Decrease) in Equity Securities, FV-NI
Gains (losses) on net investment hedges, net of tax
Derivatives used in Net Investment Hedge, Net of Tax, Period Increase (Decrease)
Gain on interest rate swap
Gain (Loss) on Derivative Instruments, Net, Pretax
Loss Contingency, Estimate of Possible Loss
Loss Contingency, Estimate of Possible Loss
Other
Stockholders' Equity, Other
Notes Payable
Notes Payable
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other
Goodwill, Other Increase (Decrease)
Fair Value by Asset Class
Asset Class [Domain]
Schedule of Variable Interest Entities [Table]
Schedule of Variable Interest Entities [Table]
Derivative asset, fair value
Derivative Asset, Subject to Master Netting Arrangement, before Offset
Other
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
Net cash flow provided by (used in) investing activities
Net Cash Provided by (Used in) Investing Activities
Fair Value
Equity Securities, FV-NI, Current
Customer [Domain]
Customer [Domain]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax
Reclassification out of Accumulated Other Comprehensive Income
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]
Components of inventory
Schedule of Inventory, Current [Table Text Block]
Interest in subsidiary (less than given percentage)
Interest In Subsidiary
Interest in subsidiary.
Debt Instrument [Axis]
Debt Instrument [Axis]
Neurimmune
Neurimmune [Member]
Neurimmune.
Litigation settlement agreement
Litigation Settlement, Expense
Effective tax rate
Effective Income Tax Rate Reconciliation, Percent
E2609 and BAN2401
E2609 and BAN2401 [Member]
E2609 and BAN2401 [Member]
Equity Securities, FV-NI, Gain (Loss), Alternative [Abstract]
Equity Securities, FV-NI, Gain (Loss), Alternative [Abstract]
Measurement Input Type [Domain]
Measurement Input Type [Domain]
Total liabilities
Liabilities
Summary of share based compensation expense associated with different programs [Abstract]
Summary of share based compensation expense associated with different programs [Abstract]
Summary of share-based compensation expense associated with different programs.
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Accumulated Other Comprehensive Income
AOCI Attributable to Parent [Member]
Measurement Frequency [Domain]
Measurement Frequency [Domain]
Property, Plant and Equipment
Property, Plant and Equipment Disclosure [Text Block]
Gains (losses) on net investment hedge
Accumulated Other Comprehensive Income (Loss), Derivative Qualifying as Hedge, Excluded Component, Including Portion Attributable to Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss) [Table]
Accumulated Other Comprehensive Income (Loss) [Table]
Disposal Groups, Including Discontinued Operations [Table]
Disposal Groups, Including Discontinued Operations [Table]
Unfunded status of postretirement benefit plans
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Collaboration profit sharing
Collaboration Profit Sharing [Member]
Collaboration Profit Sharing
Income tax effect
Share-Based Payment Arrangement, Expense, Tax Benefit
Collaboration expense
Collaboration expenses accrual
Collaboration expenses accrual
Number of reportable segments
Number of Reportable Segments
Net income per share:
Earnings Per Share [Abstract]
Earnings Per Share [Abstract]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Decrease in unrecognized tax benefits is reasonably possible
Decrease in Unrecognized Tax Benefits is Reasonably Possible
Reduction in contingent consideration
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Asset
Cumulative translation loss
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax
Other revenues
Other revenues [Table Text Block]
Other revenues [Table Text Block]
Common stock, par value $0.0005 per share
Common Stock, Value, Issued
Derivative Maturity [Domain]
Derivative Maturity [Domain]
[Domain] for Derivative Maturity [Axis]
Capital contribution from noncontrolling interest
Noncontrolling Interest, Capital Contribution
Noncontrolling Interest, Capital Contribution
Future Contingent Milestone Types [Axis]
Future Contingent Milestone Types [Axis]
Future Contingent Milestone Types [Axis]
Employee stock purchase plan
Employee Stock Purchase Plan [Member]
Employee stock purchase plan.
Due after one year through five years, estimated fair value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Litigation
Legal Matters and Contingencies [Text Block]
Total current assets
Assets, Current
Preferred stock
Preferred Stock [Member]
Analysis of change In reserves
Analysis Of Amount Of And Change In Product Revenue Reserves [Table Text Block]
Analysis of amount of and change in product revenue reserves.
Royalty operating profit threshold for highest royalty rate percentage
Royalty operating profit threshold for highest royalty rate percentage
Royalty operating profit threshold for highest royalty rate percentage
Asset impairment charges
Asset Impairment Charges
Accounts receivable
Accounts Receivable, after Allowance for Credit Loss
Contingent consideration obligations
Fair value, beginning of period
Fair value, end of period
Business Combination, Contingent Consideration, Liability
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Abstract]
Litigation settlement agreement
Effective Tax Rate Reconciliation, Litigation Agreement
Effective Tax Rate Reconciliation, Litigation Agreement
Equity in (income) loss of investee, net of tax
Income (Loss) from Equity Method Investments, Net of Tax
Income (Loss) from Equity Method Investments, Net of Tax
Amounts payable
Accounts Payable, To Collaborator
Accounts Payable, To Collaborator
Other, net
Other Nonoperating Income (Expense)
Entity Filer Category
Entity Filer Category
2.250% Senior Notes due May 1, 2030
2.25% Senior Notes due May 1, 2030 [Member]
2.25% Senior Notes due May 1, 2030 [Member]
Restructuring Type [Axis]
Restructuring Type [Axis]
Statement [Table]
Statement [Table]
Current Fiscal Year End Date
Current Fiscal Year End Date
Stock Repurchase Program, Authorized Amount
Stock Repurchase Program, Authorized Amount
Intangible Assets and Goodwill
Goodwill and Intangible Assets Disclosure [Text Block]
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
UCB Pharma S.A.
UCB Pharma S.A. [Member]
UCB Pharma S.A. [Member]
Financial Instruments
Cash, Cash Equivalents, and Marketable Securities [Text Block]
Schedule of Accumulated Other Comprehensive Income (Loss)
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Other current assets, receivable
Other Assets, Current, Fair Value Disclosure,
Other Assets, Current, Fair Value Disclosure,
State taxes
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent
Government securities
US Treasury and Government [Member]
Expected future amortization expense, 2028
Finite-Lived Intangible Asset, Expected Amortization, Year Five
Summary of roll forward of the changes in goodwill
Schedule of Goodwill [Table Text Block]
Mortgage and other asset backed securities
Asset-Backed Securities [Member]
Royalty Attributed To OCREVUS
Royalty Attributed To OCREVUS [Member]
Royalty Attributed To OCREVUS
Net cash flow provided by (used in) operating activities
Net Cash Provided by (Used in) Operating Activities
Biosimilars
Biosimilars [Member]
Biosimilars
Estimated future amortization for acquired intangible assets
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]
Marketable securities
Debt Securities, Available-for-Sale, Current
Other
Other Accrued Liabilities, Current
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table]
Other changes in operating assets and liabilities, net
Increase (Decrease) in Other Operating Assets and Liabilities, Net
Depreciation and amortization
Depreciation, Depletion and Amortization
Other (income) expense, net
Other (income) expense
Other (income) expense
Other Operating Income (Expense), Net
Unrealized Loss on Derivatives
Unrealized Loss on Derivatives
Unrealized Loss on Derivatives
Euro
Euro Member Countries, Euro
Statement of Financial Position [Abstract]
Statement of Financial Position [Abstract]
Total Biogen Inc. shareholders’ equity
Equity, Attributable to Parent
Realized gains
Debt Securities, Available-for-Sale, Realized Gain
Commercial paper
Commercial Paper [Member]
Schedule of Finite-Lived Intangible Assets [Table]
Schedule of Finite-Lived Intangible Assets [Table]
Nightstar
Nightstar [Member]
Nightstar [Member]
Deferred tax assets, unrecognized tax benefit
Deferred Tax Assets, Valuation Allowance
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Four
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Four
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Four
Finite-Lived Intangible Assets, Major Class Name [Domain]
Finite-Lived Intangible Assets, Major Class Name [Domain]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Currency translation adjustment
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax
Schedule of Stock by Class [Table]
Schedule of Stock by Class [Table]
After Second GAZYVA Threshold Date
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Three
Percentage of co promotion operating profits greater than first fifty million option two sub option three.
Gains (losses) on cash flow hedges
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Government securities Current
Government Securities Current [Member]
Government securities Current.
Revenues from anti-CD20 therapeutic programs
Revenues from anti-CD20 therapeutic programs
Revenues from anti-CD20 therapeutic programs [Table Text Block]
Revenues from anti-CD20 therapeutic programs
Investments in Variable Interest Entities
Variable Interest Entity Disclosure [Text Block]
Acquisitions of intangible assets
Payments to Acquire Intangible Assets
Collaboration agreement term
Collaboration Agreement Term
Collaboration Agreement Term
2023 and 2022 Cost Saving Initiatives
2023 and 2022 Cost Saving Initiatives [Member]
2023 and 2022 Cost Saving Initiatives
Not designated as hedging instrument
Not Designated as Hedging Instrument [Member]
Summary of activity related to Aducanumab collaboration
Summary of Activity Related to Aducanumab Collaboration [Table Text Block]
[Table Text Block] for Summary of Activity Related to Aducanumab Collaboration [Table]
Restructuring, Business Transformation and Other Cost Saving Initiatives
Restructuring and Related Activities Disclosure [Text Block]
Genentech
Roche Group Genentech Member
Roche group Genentech.
Hedging Designation [Domain]
Hedging Designation [Domain]
5.200% Senior Notes due 2045
Senior Notes Five Point Two Percent Due Twenty Forty Five [Member]
Senior Notes Five Point Two Percent Due Twenty Forty Five [Member]
Significant Other Observable Inputs (Level 2)
Fair Value, Inputs, Level 2 [Member]
Potential future milestone payments commitment to third party
Potential Future Milestone Payments Commitment To Third Party Approximately
Potential future milestone payments commitment to third party approximately.
Operating expense
Operating Expense [Member]
Net Investment Hedging
Net Investment Hedging [Member]
Entity Emerging Growth Company
Entity Emerging Growth Company
Intangible assets, net
Intangible assets, net
Intangible Assets, Net (Excluding Goodwill)
Other noncurrent assets
Other Noncurrent Assets [Member]
Solothurn, Switzerland
Solothurn, Switzerland [Member]
Solothurn, Switzerland [Member]
Loss Contingency, Information about Litigation Matters [Abstract]
Loss Contingency, Information about Litigation Matters [Abstract]
Facility Type [Axis]
Facility Type [Axis]
Facility Type
Summary of the effect of cash flow derivatives designated as hedging instruments on the condensed consolidated statements of income
Derivative Instruments, Gain (Loss) [Table Text Block]
Accelerated Depreciation and Other Costs
Accelerated Depreciation And Other Costs [Member]
Accelerated Depreciation And Other Costs
Document Fiscal Period Focus
Document Fiscal Period Focus
Workforce Reduction
Workforce Reduction [Member]
Workforce Reduction
Useful life
Finite-Lived Intangible Asset, Useful Life
Government securities Non-current
Government Securities Non-current [Member]
Government Securities Non Current.
Other revenues [Abstract]
Other revenues [Abstract]
Other revenues [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, by Antidilutive Securities [Axis]
Antidilutive Securities [Axis]
Share-based compensation
Share-Based Payment Arrangement, Noncash Expense
Common stock
Common Stock [Member]
Foreign Tax Authority
Foreign Tax Authority [Member]
Accrued income taxes
Accrued Income Taxes, Noncurrent
Marketable securities
Debt Securities, Available-for-Sale, Noncurrent
Unrealized gains (losses) on pension benefit obligation, net of tax
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax
SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis]
SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis]
City Area Code
City Area Code
Entity Address, Postal Zip Code
Entity Address, Postal Zip Code
Earnings per Share
Earnings Per Share [Text Block]
Product and Service [Axis]
Product and Service [Axis]
Investments, All Other Investments [Abstract]
Investments, All Other Investments [Abstract]
Royalty and other revenue
Royalty [Member]
Income Statement Location [Domain]
Income Statement Location [Domain]
Collaboration profit sharing/(loss reimbursement)
Collaboration profit (loss) sharing
Collaboration profit (loss) sharing
SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]
SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]
GAZYVA
GAZYVA [Member]
GAZYVA [Member]
Equity, ownership interest
Equity Method Investment, Ownership Percentage
Fair value of contingent consideration obligations
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
Document Fiscal Year Focus
Document Fiscal Year Focus
Geographical [Domain]
Geographical [Domain]
AVONEX
AVONEX [Member]
AVONEX
Total equity
Beginning balance
Ending balance
Equity, Including Portion Attributable to Noncontrolling Interest
LEQEMBI Collaboration
LEQEMBI Collaboration [Member]
LEQEMBI Collaboration
VUMERITY
VUMERITY [Member]
VUMERITY
Recognized net reductions to operating expense
Collaborative Arrangement, Profit (Loss) Sharing
Collaborative Arrangement, Profit (Loss) Sharing
Minimum
Minimum [Member]
Property, plant and equipment, net
Property, Plant and Equipment, Net
Weighted-average shares used in calculating:
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Share Repurchase Program [Domain]
Share Repurchase Program [Domain]
Performance stock units settled in cash
Performance Stock Units Settled in Cash [Member]
Performance Stock Units Settled in Cash [Member]
Payment Due At Second Anniversary
Payment Due At Second Anniversary [Member]
Payment Due At Second Anniversary
Finite-Lived Intangible Assets by Major Class [Axis]
Finite-Lived Intangible Assets by Major Class [Axis]
Other comprehensive income (loss), net of tax
Other Comprehensive Income (Loss), Net of Tax
Statement of Cash Flows [Abstract]
Statement of Cash Flows [Abstract]
Currency translation adjustments
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
PLEGRIDY
PLEGRIDY [Member]
PLEGRIDY
ASSETS
Assets [Abstract]
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets Disclosure [Abstract]
Total
Liabilities, Fair Value Disclosure
Foreign exchange (gains) losses, net
Gain (Loss), Foreign Currency Transaction, before Tax
Summary of Contractual Maturities: Available-for-Sale Securities
Available-for-Sale Securities, Debt Maturities [Abstract]
Summary of fair value and presentation of derivatives
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
Nonrelated Party
Nonrelated Party [Member]
Payments related to issuance of stock for share-based compensation arrangements, net
Payment, Tax Withholding, Share-Based Payment Arrangement
Contract manufacturing, royalty and other revenue
Product and Service, Other [Member]
Time-vested restricted stock units
Time Vested Restricted Stock Units [Member]
Time vested restricted stock units.
Other current assets
Other Current Assets [Member]
Net income
Net income
Net income
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Net cash flow provided by (used in) financing activities
Net Cash Provided by (Used in) Financing Activities
Deferred tax asset
Deferred Income Tax Assets, Net
Cash flows, revenue
Cash flows, revenue [Member]
Cash flows, revenue [Member]
Expense reflected within statements of income
Expense reflected within statements of income
Expense reflected within statements of income
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Other
Payments for (Proceeds from) Other Investing Activities
Retained earnings
Retained Earnings [Member]
Other Income (Expense), Net
Interest Income (Expense), Net [Abstract]
Share-based compensation expense included in condensed consolidated statements of income
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
Total liabilities and equity
Liabilities and Equity
Amortized Cost
Amortized Cost
Debt Securities, Available-for-Sale, Amortized Cost
Investments and other assets
Other Assets, Noncurrent
Operating lease assets
Operating Lease, Right-of-Use Asset
Unrealized gains (losses) on cash flow hedges, net of tax
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax
Basic earnings per share attributable to Biogen Inc.
Earnings Per Share, Basic
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash Equivalents, at Carrying Value [Abstract]
Schedule of Long-term Debt Instruments [Table]
Schedule of Long-Term Debt Instruments [Table]
2023 Cost Saving Initiatives
2023 Cost Saving Initiatives [Member]
2023 Cost Saving Initiatives
Accounting Policies [Abstract]
Accounting Policies [Abstract]
Amounts receivable
Accounts Receivable, From Collaborator
Accounts Receivable, From Collaborator
2020 Share Repurchase Program
2020 Share Repurchase Program [Member]
2020 Share Repurchase Program [Member]
Gain (loss) on sale
Gain (Loss) on Disposition of Assets
Share-based Compensation Expense included in consolidated statements of income
Share-Based Payment Arrangement, Recognized Amount [Abstract]
Currency [Axis]
Currency [Axis]
Mortgage and other asset backed securities Non-current
Mortgage And Other Asset Backed Securities Non Current [Member]
Mortgage And Other Asset Backed Securities Non Current.
Expected cost
Restructuring and Related Cost, Expected Cost
Payments/Returns Relating To Sales in Current Year
Payments Returns Applied Against Product Revenue Reserves Relating To Current Year
Payments/ returns applied against product revenue reserves relating to current year.
Spinal Muscular Atrophy
Spinal Muscular Atrophy [Member]
Spinal Muscular Atrophy
Pretax profit sharing formula
Pretax Profit Sharing Formula [Table Text Block]
Pretax Profit Sharing Formula [Table Text Block]
Entity Address, City or Town
Entity Address, City or Town
Related Party
Related Party [Member]
Gain/Loss on fair value of foreign currency forward contracts
Unrealized Gain (Losses) on Foreign Currency Derivatives, Net, before Tax
Amount of net unrealized gain (loss) related to the change in fair value of foreign currency exchange rate derivatives designated as cash flow hedging instruments. Recorded in accumulated other comprehensive income to the extent that the cash flow hedge is determined to be effective.
Inventory, Current [Table]
Inventory, Current [Table]
Percentage of future development costs related to Eisai
Percentage of future development costs related to Eisai
Percentage of future development costs related to Eisai
Issuance of common stock under stock option and stock purchase plans, shares
Stock Issued During Period, Shares, Treasury Stock Reissued
Schedule of Cash and Cash Equivalents [Table]
Schedule of Cash and Cash Equivalents [Table]
Consolidation
Consolidation, Policy [Policy Text Block]
RITUXAN
RITUXAN [Member]
RITUXAN.
Warehouse, Utilities and Support Space
Warehouse, Utilities and Support Space [Member]
Warehouse, Utilities and Support Space
Restructuring charges
Expense
Restructuring Charges
Document Transition Report
Document Transition Report
3.250% Senior Notes, Due February 15, 2051
3.250% Senior Notes, Due February 15, 2051 [Member]
3.250% Senior Notes, Due February 15, 2051
Schedule of Business Acquisitions, by Acquisition [Table]
Schedule of Business Acquisitions, by Acquisition [Table]
Amount remaining under 2019 Share Repurchase Program
Stock Repurchase Program, Remaining Authorized Repurchase Amount
Proceeds from sales and maturities of marketable securities
Proceeds from Sale and Maturity of Marketable Securities
Cash flows, operating expenses
Cash flows, operating expenses [Member]
Cash flows, operating expenses [Member]
Marketable debt securities
Fair value
Debt Securities, Available-for-Sale
Net gains recognized on the decrease in fair value of equity securities
Equity Securities, FV-NI, Unrealized Gain
Gross unrealized gains
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Summary of the effect of derivatives designated as net investment hedging instruments on our consolidated statement of income
Schedule of Net Investment Hedges in Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Net (gains) losses recognized on equity securities
Equity Securities, FV-NI, Gain (Loss)
Indefinite-lived Intangible Assets [Axis]
Indefinite-Lived Intangible Assets [Axis]
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Abstract]
Due after five years, estimated fair value
Available For Sale Securities Debt Maturities After Five Years Fair Value
This item represents the fair value of debt securities, which are expected to mature after five years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.
Derivative Instrument [Axis]
Derivative Instrument [Axis]
Other assets, receivable
Other Assets, Fair Value Disclosure
Adjustments to reconcile net income to net cash flow from operating activities:
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Measurement Input Type [Axis]
Measurement Input Type [Axis]
Due in one year or less, amortized cost
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One
Average maturity of marketable securities, months
Average Maturity Of Marketable Securities
Average remaining time to maturity of marketable debt securities, available-for-sale securities.
Corporate debt securities Current
Corporate Debt Securities Current [Member]
Corporate debt securities Current.
Equity Securities, Current
Equity Securities, Current [Member]
Equity Securities, Current
Comprehensive income (loss) attributable to noncontrolling interests, net of tax
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest
Until Second GAZYVA Threshold Date
Percentage Of Co Promotion Operating Profits Greater Than First Fifty Million Option Two Sub Option Two
Percentage of co promotion operating profits greater than first fifty million option two sub option two.
Overview
Business Overview [Policy Text Block]
Describes an overview of the company and its operations.
Additional paid-in capital
Additional Paid in Capital
Returns
Sales Returns and Allowances [Member]
Summary of Activity Related to BAN2401 and Elenbecestat Collaboration
Summary of Activity Related to E2609 and BAN2401 Collaboration [Table Text Block]
[Table Text Block] for Summary of Activity Related to E2609 and BAN2401 Collaboration [Table]
Other comprehensive income:
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Derivative contracts
Derivative Asset
Deferred income taxes
Deferred Income Tax Expense (Benefit)
Restructuring Plan [Axis]
Restructuring Plan [Axis]
Statement of Comprehensive Income [Abstract]
Statement of Comprehensive Income [Abstract]
Additional milestone payment
Additional Milestone Payment
Additional milestone payment.
ADUHELM
ADUHELM [Member]
ADUHELM
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table]
Expected future amortization expense, 2026
Finite-Lived Intangible Asset, Expected Amortization, Year Three
Due after five years, amortized cost
Available For Sale Securities Debt Maturities After Five Years Amortized Cost
This item represents debt securities, at cost, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any, which are expected to mature after five years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.
Total development expense incurred by the collaboration related to the advancement of LEQEMBI
Expense Incurred By Collaboration
Total expense incurred by collaboration.
Related Party, Type [Axis]
Related Party, Type [Axis]
Marketable equity securities
Debt Securities, Trading, and Equity Securities, FV-NI, Cost [Abstract]
Entity Registrant Name
Entity Registrant Name
Stock units
Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements
Taxes on foreign earnings
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent
Expected future amortization expense, 2025
Finite-Lived Intangible Asset, Expected Amortization, Year Two
Net unrealized (gains) losses recognized on equity securities
Net gains recognized on the increase in fair value of equity securities
Equity Securities, FV-NI, Unrealized Gain (Loss)
Cost of Sales
Cost of Sales [Member]
Severance Costs
Employee Severance [Member]
Noncontrolling interests
Equity, Attributable to Noncontrolling Interest
Credits and net operating loss utilization
Effective Income Tax Rate Reconciliation, Tax Credit, Percent
Payment
Payments for Restructuring
Document Period End Date
Document Period End Date
Accumulated depreciation
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment
Summary of assets and liabilities recorded at fair value
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
Revenue
Sales [Member]
Proceeds from divestiture of interest in joint venture
Proceeds from Divestiture of Interest in Joint Venture
Collaboration agreement term
Period Of Collaboration Agreement
Period Of Collaboration Agreement
Treasury stock
Treasury Stock, Common [Member]
Entity Central Index Key
Entity Central Index Key
Reclassification out of Accumulated Other Comprehensive Income
Reclassification out of Accumulated Other Comprehensive Income [Member]
Sales trigger gross sales threshold
Sales Trigger Gross Sales Threshold
Sales trigger gross sales threshold.
Liabilities:
Liabilities, Fair Value Disclosure [Abstract]
Compensation related to share-based payments
Share-based compensation expense
Share-Based Payment Arrangement, Expense
Effect of dilutive securities:
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Cost
Finite-Lived Intangible Assets, Gross
Income tax (benefit) expense
Income Tax Expense (Benefit)
Income Tax Expense (Benefit)
Finished goods
Inventory, Finished Goods, Net of Reserves
Rest of World
Non-US [Member]
Strategic investment portfolio
Strategic Investment Portfolio
Strategic investment portfolio.
Designated as hedging instrument
Designated as Hedging Instrument [Member]
FLIXABI
FLIXABI [Member]
FLIXABI [Member]
Collaboration expense
Employee-related Liabilities, Current
Fair Value Measurements
Fair Value Disclosures [Text Block]
Other Restructuring
Other Restructuring [Member]
Amounts reclassified from accumulated other comprehensive income, net of tax
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax
Total other comprehensive income (loss), net of tax
Other comprehensive income (loss), net of tax
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
Revenues by product
Disaggregation of Revenue [Table Text Block]
Inventory, Idle Capacity Charges And Contractual Commitments
Inventory, Idle Capacity Charges And Contractual Commitments [Member]
Inventory, Idle Capacity Charges And Contractual Commitments
Equity [Abstract]
Equity [Abstract]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale [Line Items]
Inventory
Inventory Disclosure [Text Block]
Entity [Domain]
Entity [Domain]
Facility Location [Axis]
Facility Location [Axis]
-- None. No documentation exists for this element. --
BIIB054
BIIB054 [Member]
BIIB054
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents [Line Items]
Amendment Flag
Amendment Flag
Legal Entity [Axis]
Legal Entity [Axis]
Unrealized Gain (Loss) on Derivatives
Unrealized Gain (Loss) on Derivatives
Money market funds
Money Market Funds [Member]
Comprehensive income (loss) attributable to noncontrolling interests, net of tax
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest
Due in one year or less, estimated fair value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One
Assets:
Assets, Fair Value Disclosure [Abstract]
Retirement of common stock pursuant to the 2020 Share Repurchase Program, at cost (in shares)
Stock Repurchased and Retired During Period, Shares
Repurchase of common stock pursuant to the 2020 Share Repurchase Program, at cost (in shares)
Repurchase of common stock, at cost (in shares)
Treasury Stock, Shares, Acquired
Estimated additional payments upon achievement of development and commercial milestones
Estimated Additional Payments Upon Achievement Of Development And Commercial Milestones
Estimated additional payments upon achievement of development and commercial milestones.
Proceeds from sales of strategic investments
Proceeds from Sale of Other Investments
Sage Therapeutics
Sage Therapeutics Inc. [Member]
Sage Therapeutics Inc.
Gain (loss) on investments in equity securities
Gain (Loss) on Securities [Table Text Block]
Proceeds from sale of equity interest in Samsung Bioepis
Proceeds from Sale of Equity Method Investments
Diluted earnings per share attributable to Biogen Inc.
Shares used in calculating diluted earnings per share
Weighted Average Number of Shares Outstanding, Diluted
Amortization and impairment of acquired intangible assets
Amortization and Impairment of Acquired Intangible Assets
Amortization and Impairment of Acquired Intangible Assets
MS Product Revenues
MS Product Revenues [Member]
MS Product Revenues [Member]
Limit of gross sale of GAZYVA to be achieved in preceding 12 months under option one
Threshold Of Gross Sales Of To Be Achieved In Preceding Twelve Consecutive Months Under Option One
Threshold of gross sales of to be achieved in preceding twelve consecutive months under option one.
Intangible assets
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Revenues
Revenue from Contract with Customer [Text Block]
Research and development asset [Axis]
Research and development asset [Axis]
Research and development asset [Axis]
Realized losses
Debt Securities, Available-for-Sale, Realized Loss
Purchases of property, plant and equipment
Payments to Acquire Property, Plant, and Equipment
Contract manufacturing revenue
Contract manufacturing and other revenue [Member]
Other corporate revenues [Member]
Additional paid-in capital
Additional Paid-in Capital [Member]
Less: Net (gains) losses realized on equity securities
Net gains (losses) realized during the period on equity securities
Equity Securities, FV-NI, Realized Gain (Loss)
Balance Sheet Location [Axis]
Balance Sheet Location [Axis]
Total assets
Assets
(Gain) loss on equity method investments
(Gain) loss on equity method investments
Income (Loss) from Equity Method Investments
Share Repurchase Program [Axis]
Share Repurchase Program [Axis]
Cover [Abstract]
Cover [Abstract]
Issuance of common stock under stock option and stock purchase plans
Stock Issued During Period, Value, Treasury Stock Reissued
U.S.
UNITED STATES
Fair Value, Recurring
Fair Value, Measurements Recurring
Fair Value, Recurring [Member]
FAMPYRA
FAMPYRA [Member]
FAMPYRA [Member]
Restructuring and Related Activities [Abstract]
Other long-term liabilities
Other Liabilities, Noncurrent
Other income (expense)
Other Nonoperating Income (Expense) [Member]
Income Tax Contingency [Line Items]
Income Tax Contingency [Line Items]
Operating Expenses
Operating Expenses
Eisai
Eisai [Member]
Eisai [Member]
Cash flows from financing activities:
Net Cash Provided by (Used in) Financing Activities [Abstract]
Income before income tax expense and equity in loss of investee, net of tax
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest
Co-promotion operating profit threshold for Rituxan in US and Canada to determine share of co promotion operating profit prior to amendment
Co Promotion Operating Profit Threshold To Determine Share Of Co Promotion Operating Profit Prior To Amendment
Co promotion operating profit threshold to determine share of co promotion operating profit prior to amendment.
Equity Component [Domain]
Equity Component [Domain]
Distributor One
Distributor One [Member]
Distributor one.
Amortized Cost
Equity Securities, FV-NI, Cost
Mosunetuzumab
Mosunetuzumab [Member]
Mosunetuzumab
Work in process
Inventory, Work in Process, Net of Reserves
Gain (loss) recognized in net income, excluded component
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Scenario [Axis]
Scenario [Axis]
Debt Instrument [Line Items]
Debt Instrument [Line Items]
Basic earnings per share attributable to Biogen Inc.
Weighted average number of common shares outstanding
Weighted Average Number of Shares Outstanding, Basic
Entity Current Reporting Status
Entity Current Reporting Status
(Gains) losses on investments, net
Realized Investment Gains (Losses)
Basic and diluted earnings per share
Basic And Diluted Earnings Per Share [Abstract]
Basic and diluted earnings per share.
Summary of Activity Related to Denali Therapeutics Collaboration
Summary of Activity Related to Denali Therapeutics Collaboration [Table Text Block]
Summary of Activity Related to Denali Therapeutics Collaboration
Consolidated Entities [Domain]
Consolidated Entities [Domain]
Summary of Activity Related to Sage Therapeutics
Summary of Activity Related to Sage Therapeutics [Table Text Block]
Summary of Activity Related to Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity Securities, Non-Current
Equity Securities, Non-Current [Member]
Equity Securities, Non-Current
Statement [Line Items]
Statement [Line Items]
Scenario [Domain]
Scenario [Domain]
Gains (losses) on net investment hedge, excluded component
Derivatives used in net investment hedge, net of tax, excluded component increase (decrease)
Derivatives used in net investment hedge, net of tax, excluded component increase (decrease)
Marketable debt and equity securities
Debt Securities, Available-for-Sale [Table Text Block]
Type of Restructuring [Domain]
Type of Restructuring [Domain]
Equity:
Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Reclassification out of Accumulated Other Comprehensive Income [Domain]
Reclassification out of Accumulated Other Comprehensive Income [Domain]
Noncontrolling interest
Noncontrolling Interest [Member]
Accelerated Depreciation and Other Costs
Other Restructuring Costs
Revenue from anti-CD20 therapeutic programs
Revenues from anti-cd20 therapeutic programs [Member]
Revenues from anti-cd20 therapeutic programs