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Collaborative Arrangement and Arrangement Other than Collaborative [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Short-term debt securities Debt Securities [Member] Distributor Two Distributor Two [Member] Distributor two. 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. 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Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Income before income tax provision and the income tax expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Contingent discount on common shares Payables To Divestiture Of Interest In Joint Venture, Contingent Discount on Shares, Percent Payables To Divestiture Of Interest In Joint Venture, Contingent Discount on Shares, Percent 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] Operating lease liability, current Operating Lease, Liability, Current Shares issued under ESPP (in shares) Shares issued under the 2015 ESPP (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Proceeds from sales and maturities of marketable securities Proceeds from maturities and sales Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale Preferred stock, par value $0.001 per share Preferred Stock, Value, Outstanding 2026 Lessee, Operating Lease, Liability, to be Paid, Year Three Research and development asset [Domain] Research and development asset [Domain] Research and development asset [Domain] Net Finite-Lived Intangible Assets, Net Priority review voucher Priority Review Voucher [Member] Priority Review Voucher Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] New Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Revenue from anti-CD20 therapeutic programs Revenues From Anti-CD20 Therapeutic Programs [Member] Revenues From Anti-CD20 Therapeutic Programs Collaborative Arrangement, Profit (Loss) Sharing Components [Axis] Collaborative Arrangement, Profit (Loss) Sharing Components [Axis] Collaborative Arrangement, Profit (Loss) Sharing Components Counterparty Name [Domain] Counterparty Name [Domain] Accumulated Amortization Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Separately recognized transactions, additional disclosures, acquisition cost expensed Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed 2025 Lessee, Operating Lease, Liability, to be Paid, Year Two Facility Location [Domain] Facility Location [Domain] -- None. No documentation exists for this element. -- Option exercise fee Research And Development Expense, Option Exercise Fee Research And Development Expense, Option Exercise Fee Interest income Investment Income, Interest Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Foreign Income (Loss) from Continuing Operations before Income Taxes, Foreign Consideration transferred Business Combination, Consideration Transferred Ratio of total number of shares reserved under the plan Ratio Of Number Of Shares Reserved Under Plan Ratio of total number of shares reserved under the plan. 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Cost and expense: Costs and Expenses [Abstract] Option exercise fee Contract Option Exercise Fee Contract Option Exercise Fee Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period Title of 12(b) Security Title of 12(b) Security Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Due from joint venture Payables To Divestiture Of Interest In Joint Venture Payables To Divestiture Of Interest In Joint Venture 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. Depreciation, amortization and other Deferred Tax Liabilities Depreciation Amortization Other Deferred tax liabilities depreciation amortization other. Extinguishment of Debt [Axis] Extinguishment of Debt [Axis] Sublease income Sublease Income Acquisitions Business Combination Disclosure [Text Block] Cost and net Indefinite-Lived Intangible Assets (Excluding Goodwill) Summary of unrealized gain (loss) on derivative instruments that are included in AOCI Derivative Instruments, Unrealized Gain (Loss) [Table Text Block] Derivative Instruments, Unrealized Gain (Loss) Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Weighted average grant date fair value, nonvested Beginning balance, unvested (in dollars per share) Ending balance, unvested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] Entity Tax Identification Number Entity Tax Identification Number Other Segment Geographical Groups Of Countries Group Other [Member] Segment geographical groups of countries group other. Net lease cost Lease, Cost Payment Due At First Anniversary Payment Due At First Anniversary [Member] Payment Due At First Anniversary Inventory, other reserves and accruals Deferred Tax Assets, Inventory Capitalized share-based compensation costs Share-Based Payment Arrangement, Amount Capitalized Statistical Measurement [Axis] Statistical Measurement [Axis] Administrative Space Administrative Space [Member] Administrative Space Balance Sheet Location [Domain] Balance Sheet Location [Domain] Entity Interactive Data Current Entity Interactive Data Current Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] 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] Product revenue, net Total product revenue Product [Member] Completed Technology Completed Technology [Member] Completed Technology Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Outstanding equity awards Payments to Acquire Businesses, Gross, Outstanding Equity Awards Payments to Acquire Businesses, Gross, Outstanding Equity Awards Purchase of common stock Purchase of common stock Purchase of common stock Share-based Compensation Arrangement by Share-based Payment Award Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Total Interferon Interferon [Member] Interferon Measure: Measure [Axis] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Name Outstanding Recovery, Individual Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Advertising costs Advertising Expense Research and development costs, percentage Research and Development Costs, Percentage Research and Development Costs, Percentage Business Acquisition, Contingent Consideration [Line Items] Business Acquisition, Contingent Consideration [Line Items] Components of deferred tax assets and liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Shares issued under employee stock purchase plan Shares Issued Under Employee Stock Purchase Plan [Table Text Block] Shares issued under employee stock purchase plan. Counterparty Name [Axis] Counterparty Name [Axis] Derivative Instruments and Hedging Activities Derivatives, Policy [Policy Text Block] Antidilutive Securities Excluded from Computation of Earnings Per Share Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] 2023 Term loan three-year tranche 2023 Term Loan Three-Year Tranche [Member] 2023 Term Loan Three-Year Tranche 2024 Finite-Lived Intangible Asset, Expected Amortization, Year One Cash paid for amounts included in the measurement of lease liabilities Operating Lease, Payments 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] Common stock outstanding, beginning balance (in shares) Common stock outstanding, ending balance (in shares) Common stock outstanding (in 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 Income tax (benefit) expense: Income Tax Expense (Benefit), Continuing Operations [Abstract] Net Gains/(Losses) Recognized in Operating Income (in millions) Gain (Loss) on Derivative Instruments, Net, Pretax PEO PEO [Member] Loss contingency Loss Contingency, Estimate of Possible Loss Concentration of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Other Stockholders' Equity, Other Auditor Location Auditor Location Employee Benefit Plans Retirement Benefits [Text Block] Performance stock units settled in stock activity Performance Stock Units Settled in Stock [Table Text Block] Performance Stock Units Settled in Stock [Table Text Block] Defined Contribution Plan Disclosure [Line Items] Defined Contribution Plan Disclosure [Line Items] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Net cash flow provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Fair Value Equity Securities, FV-NI, Current Net Gains/(Losses) Reclassified from AOCI into Operating Income (in millions) Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Interest in subsidiary (less than given percentage) Interest In Subsidiary Interest in subsidiary. Summary of activity related to BAN2401 and Elenbecestat collaboration Summary Of Activity Related To Collaboration With Company Eight [Table Text Block] [Table Text Block] Summary Of Activity Related To Collaboration With Company Eight [Table Text Block] [Table Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Germany GERMANY Neurimmune Neurimmune Neurimmune [Member] Neurimmune. 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Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Neurimmune's tax basis in ADUHELM Deferred Tax Assets, Counterparty Tax Basis in Asset Deferred Tax Assets, Counterparty Tax Basis in Asset State Current State and Local Tax Expense (Benefit) Total current assets Assets, Current 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. Periodic pension cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) 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 Impairment of assets Asset Impairment Charges Contingent consideration obligations Fair value, beginning of year Fair value, end of year Business Combination, Contingent Consideration, Liability 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 Amortization Amortization Restructuring Type [Axis] Restructuring Type [Axis] Schedule of Stock Options Roll Forward Schedule of Stock Options Roll Forward [Table Text Block] Earnings per Share Earnings Per Share, Policy [Policy Text Block] Intangible Assets and Goodwill Goodwill and Intangible Assets Disclosure [Text Block] Financial Instruments Cash, Cash Equivalents, and Marketable Securities [Text Block] Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Other current assets, receivable Receivable from Samsung BioLogics 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 Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Government securities US Treasury and Government [Member] 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Five Deferred Compensation Plan Other Postretirement Benefits Plan [Member] Mortgage and other asset backed securities Asset-Backed Securities [Member] Net cash flow provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Internal reorganization Effective Income Tax Rate Reconciliation, Intellectual Property Rights Reorganization Effective Income Tax Rate Reconciliation, Intellectual Property Rights Reorganization Estimated future amortization of intangible assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Class of Stock [Axis] Class of Stock [Axis] 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 Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Sangamo Therapeutics, Inc. Agreement Sangamo Therapeutics, Inc. Agreement [Member] Sangamo Therapeutics, Inc. Agreement Number of days for calculation of average closing stock price Number Of Days For Calculation Of Average Closing Stock Price Number of days for calculation of average closing stock price. Depreciation and amortization Depreciation, Depletion and Amortization Other (income) expense Other Operating Income (Expense), Net Furniture and Fixtures Furniture and Fixtures [Member] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Lease Arrangement, Type [Domain] Lease Contractual Term [Domain] Payment terms of accounts receivable arising from product sales Payment Terms Of Accounts Receivable Payment terms of accounts receivable. General Business General Business Tax Credit Carryforward [Member] Business Combination and Asset Acquisition [Abstract] Realized gains Debt Securities, Available-for-Sale, Realized Gain Commercial paper Commercial Paper [Member] Other long-lived assets Long-lived assets Long-Lived Assets Valuation allowance Valuation allowance Deferred Tax Assets, Valuation Allowance Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] 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 After First Threshold Date until the Second Threshold Date 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. Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax Gains (losses) on cash flow hedges Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Sublease Sublease [Member] Sublease [Member] Investments in Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Deferred tax liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities 125 Broadway Building 125 Broadway Building [Member] 125 Broadway Building 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] Floating Rate 364-Day Tranche Floating Rate 364-Day Tranche [Member] Floating Rate 364-Day Tranche Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Entity Emerging Growth Company Entity Emerging Growth Company Intangible assets, net Net Intangible Assets, Net (Excluding Goodwill) Solothurn, Switzerland Solothurn, Switzerland [Member] Solothurn [Member] Other Other [Member] Other Contingent payable to blackstone Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability Loss Contingency, Information about Litigation Matters [Abstract] Loss Contingency, Information about Litigation Matters [Abstract] Facility Type [Axis] Facility Type [Axis] Facility Type Accelerated Depreciation and Other Costs Accelerated Depreciation And Other Costs [Member] Accelerated Depreciation And Other Costs Measurement Period Adjustments, Goodwill Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill Intangible assets: Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles 2024 Lessee, Operating Lease, Liability, to be Paid, Year One Government securities Non-current Government Securities Non-current [Member] Government Securities Non Current. Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Title Trading Arrangement, Individual Title Number of ophthalmolgy biosimilar products Number of Ophthalmolgy Biosimilar Products, Exclusive Rights Number of Ophthalmolgy Biosimilar Products, Exclusive Rights Numerator: Numerator [Abstract] Numerator. Common stock Common Stock [Member] 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 Individual: Individual [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Collaboration profit (loss) sharing Collaboration profit (loss) sharing Collaboration profit (loss) sharing Statute expirations Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Royalty and other revenue Royalty [Member] Income Statement Location [Domain] Income Statement Location [Domain] Income Statement Location [Domain] Investments, All Other Investments [Abstract] Investments, All Other Investments [Abstract] Estimated Fair Value Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] GAZYVA GAZYVA [Member] GAZYVA [Member] Fair value of contingent consideration obligations Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Total equity Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest Distribution to noncontrolling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Future contingent payment for annual worldwide net sales that exceeding threshold, percentage Future Contingent Payment For Annual Worldwide Net Sales That Exceed $2.0 Billion Future Contingent Payment For Annual Worldwide Net Sales That Exceed $2.0 Billion Net interest expense Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Minimum Minimum Minimum [Member] Property, plant and equipment, net Total property, plant and equipment, net Property, Plant and Equipment, Net Weighted-average shares used in calculating: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Performance stock units settled in cash PSUs 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 Other comprehensive income (loss), net of tax Net current period other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Employee benefit plan obligations Defined Benefit Plan, Benefit Obligation Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest [Member] ASSETS Assets [Abstract] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Proceeds from borrowings Proceeds from Issuance of Long-Term Debt Percentage of earnings of the target number of units granted based on actual stock performance Maximum Target Number Of Market Stock Units Granted Based On Stock Performance In Percent Maximum target number of market stock units granted based on stock performance in percent. 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(in dollars per share) Earnings Per Share, Basic Cash received under the 2015 ESPP Stock Issued During Period, Value, Employee Stock Purchase Plan Accounting Policies [Abstract] Accounting Policies [Abstract] Class of Treasury Stock [Table] Class of Treasury Stock [Table] Foreign currency and other adjustments Restructuring Reserve, Accrual Adjustment Gain (loss) on sale Gain (Loss) on Disposition of Assets Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Deferred tax asset, net Deferred Tax Assets, Net 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. Operating lease liabilities Operating lease liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Operating Lease Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Operating Lease Liabilities Payments made to termination agreement Payments Made To Termination Agreement Payments Made To Termination Agreement Measurement Period Adjustments, Inventory Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory Pretax profit sharing formula Pretax Profit Sharing Formula [Table Text Block] Pretax Profit Sharing Formula [Table Text Block] Current portion of notes payable and term loan Current Portion Of Notes Payable And Term Loan [Member] Current Portion Of Notes Payable And Term Loan Future contingent payment threshold Future Contingent Payment Threshold Future Contingent Payment Threshold Sale of Samsung Bioepis Effective Income Tax Rate Reconciliation, Disposition of Business, Percent Income taxes paid Income Taxes Paid Consolidation Consolidation, Policy [Policy Text Block] Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] RITUXAN RITUXAN [Member] RITUXAN. Warehouse, Utilities and Support Space Warehouse, Utilities and Support Space [Member] Warehouse, Utilities and Support Space Acquired in-process research and development Payments to Acquire in Process Research and Development, Operating Activities Payments to Acquire in Process Research and Development, Operating Activities Related cost-sharing reduction (as a percentage) Related Party Costs, Change Of Control, Reduction In Cost Sharing, Percentage Related Party Costs, Change Of Control, Reduction In Cost Sharing, Percentage Document Transition Report Document Transition Report Award Timing Predetermined Award Timing Predetermined [Flag] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Entity Public Float Entity Public Float 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] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Due after five years 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] Valuation allowance increase (decrease) Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Long-term debt, gross Notes payable and term loan Long-Term Debt, Gross All Trading Arrangements All Trading Arrangements [Member] Due in one year or less Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One All Adjustments to Compensation All Adjustments to Compensation [Member] Restructuring Reserve [Roll Forward] Restructuring Reserve [Roll Forward] Common stock, par value $0.0005 per share Common Stock, Value, Outstanding Assumptions used in valuation of market based stock units Assumptions Used In Valuation Of Market Based Stock Units [Table Text Block] Assumptions used in valuation of market based stock units. Corporate debt securities Current Corporate Debt Securities Current [Member] Corporate debt securities Current. Intangible asset, fair value Finite-Lived Intangible Assets, Fair Value Disclosure Compensation Amount Outstanding Recovery Compensation Amount Repayments of short-term debt, maturing in more than three months Repayments of Short-Term Debt, Maturing in More than Three Months After LUNSUMIO Approval until the First Threshold Date 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. Gain (Loss) on Termination of Lease Gain (Loss) on Termination of Lease Business Overview Business Overview [Policy Text Block] Describes an overview of the company and its operations. New Anti Cd20 New Anti Cd20 [Member] New Anti-CD20. Returns Sales Returns and Allowances [Member] Other comprehensive income: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Deferred income taxes Total deferred Deferred Income Tax Expense (Benefit) Subsequent Event Type [Axis] Subsequent Event Type [Axis] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] ADUHELM ADUHELM [Member] ADUHELM Forfeited (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Document Financial Statement Error Correction Document Financial Statement Error Correction [Flag] Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Due after five years 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. Accrued milestone payment Accrued Milestone Payments Accrued Milestone Payments Total development expense incurred by the collaboration related to the advancement of LEQEMBI Expense Incurred By Collaboration Total expense incurred by collaboration. Equity Method of Accounting Equity Method Investments [Policy Text Block] Acquired and in-licensed rights and patents Acquired And In Licensed Rights And Patents [Member] Acquired And In Licensed Rights And Patents 2024 Long-Term Debt, Maturity, Year One Acorda Acorda [Member] Acorda. Average stock price on grant date maximum Average Stock Price On Grant Date In Dollars Maximum Average stock price on grant date in dollars maximum. Marketable equity securities: Debt Securities, Trading, and Equity Securities, FV-NI, Cost [Abstract] Machinery and equipment Machinery and Equipment, Gross Dilutive securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Net unrealized (gains) losses recognized on equity securities Equity Securities, FV-NI, Unrealized Gain (Loss) Proceeds from divestiture of Hillerød, Denmark manufacturing operations Proceeds from Sale of Property, Plant, and Equipment Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Percent GILTI Deferred tax liabilities, GILTI tax calculation Deferred tax liabilities, GILTI tax calculation Payment Payments for Restructuring Document Period End Date Document Period End Date Amortization and impairment of acquired intangible assets Amortization and Impairment of Acquired Intangible Assets Amortization and Impairment of Acquired Intangible Assets Adoption Date Trading Arrangement Adoption Date Revenue Sales [Member] Collaboration agreement term Period Of Collaboration Agreement Period Of Collaboration Agreement Treasury stock Treasury Stock, Common [Member] Collaboration profit sharing/(loss reimbursement) Collaboration Profit (Loss) Sharing Payments are made to Elan for their share of rest of world net operating profits to effect an equal sharing of collaboration operating profit. These payments include the reimbursement of our portion of third-party royalties that Elan pays on behalf of the collaboration, relating to sales outside of the U.S. These amounts are reflected in the collaboration profit sharing line in our consolidated statement of income. As sales of TYSABRI outside the U.S. increase, our collaboration profit sharing expense will increase. 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. Gain on sale of building Gain on sale of building Gain (Loss) on Disposition of Property Plant Equipment Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Income tax (benefit) expense Income tax (benefit) expense Total income tax (benefit) expense Income Tax Expense (Benefit) Rest of World Non-US [Member] Deferred compensation liability Deferred Compensation Liability, Classified, Noncurrent Designated as Hedging Instrument Designated as Hedging Instrument [Member] FLIXABI FLIXABI [Member] FLIXABI [Member] Swiss Federal Tax Administration (FTA) Swiss Federal Tax Administration (FTA) [Member] Fair Value Measurements Fair Value Disclosures [Text Block] Number of operating segments Number of Operating Segments Amounts reclassified from AOCI Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Equity [Abstract] Equity [Abstract] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Inventory Inventory Disclosure [Text Block] Weighted average remaining lease term in years Operating Lease, Weighted Average Remaining Lease Term Total assets acquired and liabilities assumed Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Unrealized gain (loss) on derivative instruments Net unrealized gains (losses) Unrealized Gain (Loss) on Derivatives Money market funds Money Market Funds [Member] Tax credit carryforward, amount Tax Credit Carryforward, Amount Proceeds from sale of building Payments to Acquire Businesses, Net of Cash Acquired Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Credit Facility [Domain] Credit Facility [Domain] Retirement of common stock pursuant to the share repurchase program, at cost (in shares) Stock Repurchased and Retired During Period, Shares Repurchase of common stock pursuant to the 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. Property, plant and equipment, useful life Property, Plant and Equipment, Useful Life Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Claims asserted Loss Contingency, Damages Sought, Value Measurement Period Adjustments, Total identifiable net assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Net Proceeds from sales of strategic investments Proceeds from Sale of Equity Method Investments Auditor Information [Abstract] Auditor Information [Abstract] Development of product candidate expense Research and Development Expense, Development Of Product Candidate Research and Development Expense, Development Of Product Candidate Subtotal: Multiple Sclerosis MS Product Revenues [Member] MS Product Revenues [Member] Cancellable future commitments Other Commitment Tax credits Deferred Tax Liabilities, Tax Credit Carryforwards Deferred Tax Liabilities, Tax Credit Carryforwards Intangible Assets, Net (Excluding Goodwill) [Abstract] Intangible Assets, Net (Excluding Goodwill) [Abstract] Revenue Revenue from Contract with Customer [Text Block] Average stock price on grant date minimum Average Stock Price On Grant Date In Dollars Minimum Average stock price on grant date in dollars minimum. Settlement payment Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Contract manufacturing revenue Contract manufacturing and other revenue [Member] Other corporate revenues [Member] Additional paid-in capital Additional Paid-in Capital [Member] Document Annual Report Document Annual Report Less: Net (gains) losses realized on equity securities Equity Securities, FV-NI, Realized Gain (Loss) Balance Sheet Location [Axis] Balance Sheet Location [Axis] (Gain) loss on equity method investment Income (loss) from equity method investments Biogen's share of reimbursement from Eisai of ADUHELM milestone payments reflected in collaboration profit sharing/(loss reimbursement) in our consolidated statements of income Income (Loss) from Equity Method Investments Loss Contingencies [Line Items] Loss Contingencies [Line Items] Cover [Abstract] Cover [Abstract] United States U.S. UNITED STATES Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Fair Value, Recurring Fair value, measurements, recurring Fair Value, Recurring [Member] Other long-term liabilities Other Liabilities, Noncurrent Total lease payments Lessee, Operating Lease, Liability, to be Paid Supplemental cash flow information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Remaining performance obligation, amount Revenue, Remaining Performance Obligation, Amount Other (income) expense, net Other Nonoperating Income (Expense) [Member] Operating expenses Operating expense Operating Expenses Eisai Eisai [Member] Eisai [Member] Segment Information Segment Reporting Disclosure [Text Block] Acquired in-process research and development Acquired In-Process Research And Development Acquired In-Process Research And Development Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] 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. Secured Debt Secured Debt [Member] Operating lease, renewal term Lessee, Operating Lease, Renewal Term Equity Component [Domain] Equity Component [Domain] Distributor One Distributor One [Member] Distributor one. Other assets and liabilities, net Business Combination, Recognized Identifiable Assets Acquired and (Liabilities) Assumed, Assets, Other Assets And Liabilities, Net Business Combination, Recognized Identifiable Assets Acquired and (Liabilities) Assumed, Assets, Other Assets And Liabilities, Net State and Local Jurisdiction State and Local Jurisdiction [Member] Work in process Inventory, Work in Process, Net of Reserves Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] 2015 Senior Notes 2015 Senior Notes [Member] 2015 Senior Notes Entity Current Reporting Status Entity Current Reporting Status Consolidated Entities [Domain] Consolidated Entities [Domain] Prepaid research and discovery services Prepaid Expense and Other Assets 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] Marketable equity securities, non-current Equity Securities, Non-Current [Member] Equity Securities, Non-Current Property, Plant and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Scenario [Domain] Scenario [Domain] Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract] Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Outstanding borrowings Long-Term Line of Credit Net Gains/(Losses) Recognized in Other Comprehensive Income (Amounts Excluded from Effectiveness Testing) (in millions) 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) Income before income tax (benefit) expense: Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest [Abstract] Type of Restructuring [Domain] Type of Restructuring [Domain] Equity: Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Reata Pharmaceuticals, Inc Reata Pharmaceuticals, Inc [Member] Reata Pharmaceuticals, Inc Accelerated Depreciation and Other Costs Other Restructuring Costs 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] Liabilities associated with uncertain tax positions Liability for Uncertainty in Income Taxes, Current Property, plant and equipment, additions Property, Plant and Equipment, Additions 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 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Pay vs Performance Disclosure [Line Items] Entity Voluntary Filers Entity Voluntary Filers License fee License Fee License Fee Statistical Measurement [Domain] Statistical Measurement [Domain] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Royalties and licensing fees Accrued Royalties, Current Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Beginning balance, unvested (in shares) Ending balance, unvested shares (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Remaining lease term Lessee, Operating Lease, Remaining Lease Term Indebtedness Debt Disclosure [Text Block] Component of accrued expense and other Other Current Liabilities [Member] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Revolving Credit Facility Revolving Credit Facility [Member] Payments/credits relating to sales in prior years 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 MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Performance Units (PUs) Performance units Performance Shares [Member] Segment Reporting [Abstract] Segment Reporting [Abstract] Accounts payable Accounts Payable, Current Weighted average remaining contractual term for options exercisable Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Restatement Determination Date: Restatement Determination Date [Axis] Equity Method Investee, Name [Axis] Investment, Name [Axis] Investment, Name [Axis] Corporate debt securities Corporate Debt Securities [Member] Other (income) expense, net Other (income) expense Nonoperating Income (Expense) Statutory rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Accrued expense and other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accrued expense And Other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accrued expense And Other Commitments, contingencies and guarantees (Notes 22 and 23) Commitments and Contingencies Impairment of intangible assets Impairment of Intangible Assets, Indefinite-Lived (Excluding Goodwill) Construction in progress Construction in Progress, Gross 2020 Share Repurchase Program Share Repurchase Program 5 [Member] Share Repurchase Program 5 Tax Credit Carryforward [Table] Tax Credit Carryforward [Table] TYSABRI TYSABRI product [Member] TYSABRI product [Member] Expected license fee and regulatory milestone payments Expected License Fee And Regulatory Milestone Payments Expected license fee and regulatory milestone payments. Schedule of Goodwill [Table] Schedule of Goodwill [Table] Geographical [Axis] Geographical [Axis] 2022 Cost Saving Initiative 2022 Cost Saving Initiatives [Member] 2022 Cost Saving Initiatives Reata acquisition-related accrued expense Settlement Liabilities, Current Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Foreign Plan Foreign Plan [Member] Income Taxes Income Tax Disclosure [Text Block] Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1) Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO(1) Share Of Co Promotion Profits Share of co promotion profits. 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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 Acquisitions of intangible assets Payments to Acquire Intangible Assets QALSODY QALSODY [Member] QALSODY 2017 Tax Act U.S. 2017 Tax Act [Member] U.S. 2017 Tax Act Not designated as hedging instrument Not Designated as Hedging Instrument [Member] Restructuring 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 September 15, 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 approximately Potential future milestone payments commitment, approximately Potential Future Milestone Payments Commitment To Third Party Approximately Potential future milestone payments commitment to third party approximately. 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