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Acquisitions, Research Collaborations and License Agreements - Narrative (Details) $ / shares in Units, € in Millions, shares in Millions, $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
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Apr. 30, 2021 USD ($) | Mar. 31, 2021 USD ($) | Jan. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Oct. 31, 2020 USD ($) | Sep. 30, 2020 USD ($) $ / shares shares | Sep. 30, 2020 EUR (€) | Jul. 31, 2020 USD ($) | Jun. 30, 2020 USD ($) | Jan. 31, 2020 USD ($) | Dec. 31, 2021 USD ($) $ / shares | Sep. 30, 2021 USD ($) | Dec. 31, 2020 USD ($) | Sep. 30, 2020 USD ($) $ / shares shares | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) $ / shares shares | Dec. 31, 2020 USD ($) | Jan. 16, 2020 USD ($) | Dec. 31, 2019 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  | $ 2,445.0 |  | $ 3,349.0 | $ 9,177.0 | $ 7,609.0 |  |  |
Reduction to research and development expenses |  |  |  |  | $ 6.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent consideration |  |  |  | $ 841.0 |  | $ 829.0 |  |  |  |  |  | 902.0 | $ 841.0 | 829.0 | 902.0 | 829.0 | $ 841.0 |  | $ 767.0
Goodwill |  |  |  | 18,882.0 |  |  |  |  |  |  |  | 18,862.0 | 18,882.0 |  | 18,862.0 |  | 18,882.0 |  |
Decrease in contingent consideration liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (73.0) | (71.0) |  |  |
Inventories |  |  |  | 5,554.0 |  |  |  |  |  |  |  | $ 5,603.0 | 5,554.0 |  | 5,603.0 |  | 5,554.0 |  |
Pandion Therapeutics |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration transferred, asset acquisition | $ 1,900.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Transaction cost, asset acquisition | 147.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,700.0 |  |  |  |
OncoImmune |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration transferred, asset acquisition |  |  |  | 423.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net assets (liabilities) |  |  |  | (22.0) |  |  |  |  |  |  |  |  | $ (22.0) |  |  |  | $ (22.0) |  |
Amount paid for investment |  |  |  | $ 50.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  | 20.00% |  |  |  |  |  |  |  |  | 20.00% |  |  |  | 20.00% |  |
Value of investment |  |  |  | $ 33.0 |  |  |  |  |  |  |  |  | $ 33.0 |  |  |  | $ 33.0 |  |
Premium on shares acquired |  |  |  | 17.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 462.0 |  |
Dunboyne |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration transferred, asset acquisition |  |  |  |  |  | 302.0 | € 256 |  |  |  |  |  |  |  |  |  |  |  |
Net assets (liabilities) |  |  |  |  |  | 13.0 |  |  |  |  |  |  |  | 13.0 |  | 13.0 |  |  |
Property, plant and equipment |  |  |  |  |  | 289.0 |  |  |  |  |  |  |  | 289.0 |  | 289.0 |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Premium on shares acquired |  |  |  |  |  | 22.0 |  |  |  |  |  |  |  |  |  |  |  |  |
COVID-19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Charges related to program discontinuation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 207.0 |  |  |  |
Sentinel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration transferred, asset acquisition |  |  |  |  |  |  |  | $ 410.0 |  |  |  |  |  |  |  |  |  |  |
Inventories |  |  |  |  |  |  |  | 9.0 |  |  |  |  |  |  |  |  |  |  |
Sentinel | Technology Rights |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquired intangible assets |  |  |  |  |  |  |  | $ 401.0 |  |  |  |  |  |  |  |  |  |  |
Acceleron Pharma Inc. | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price in acquisition of business (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 180 |  |  |  |  |  |  |  |
Payment to acquire business |  |  |  |  |  |  |  |  |  |  | $ 11,500.0 |  |  |  |  |  |  |  |
Termination fee to be paid by acquiree in acquisition of business |  |  |  |  |  |  |  |  |  |  | 345.0 |  |  |  |  |  |  |  |
Acceleron Pharma Inc. | Minimum | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse termination fee in acquisition of business |  |  |  |  |  |  |  |  |  |  | 650.0 |  |  |  |  |  |  |  |
Acceleron Pharma Inc. | Maximum | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse termination fee in acquisition of business |  |  |  |  |  |  |  |  |  |  | $ 750.0 |  |  |  |  |  |  |  |
Pandion Therapeutics |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net assets (liabilities) | $ 156.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Themis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment to acquire business |  |  |  |  |  |  |  |  | $ 366.0 |  |  |  |  |  |  |  |  |  |
Contingent consideration, maximum |  |  |  |  |  |  |  |  | 740.0 |  |  |  |  |  |  |  |  |  |
Contingent consideration |  |  |  |  |  |  |  |  | 85.0 |  |  |  |  |  |  |  |  |  |
In-process research and development |  |  |  |  |  |  |  |  | 113.0 |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  |  |  |  |  |  |  |  | 59.0 |  |  |  |  |  |  |  |  |  |
Deferred tax assets |  |  |  |  |  |  |  |  | 72.0 |  |  |  |  |  |  |  |  |  |
Other assets (liabilities), net |  |  |  |  |  |  |  |  | (32.0) |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  |  | $ 239.0 |  |  |  |  |  |  |  |  |  |
Future milestone payments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 450.0 |  |
Themis | COVID-19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment charge |  |  |  |  |  |  |  |  |  |  |  |  | 90.0 |  |  |  |  |  |
Decrease in contingent consideration liability |  |  |  |  |  |  |  |  |  |  |  |  | 45.0 |  |  |  |  |  |
ArQule |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment to acquire business |  |  |  |  |  |  |  |  |  | $ 2,700.0 |  |  |  |  |  |  |  |  |
In-process research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,280.0 |
Cash and cash equivalents |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 145.0 |
Other assets (liabilities), net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 34.0 |
Goodwill |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 512.0 |
Share-based compensation payments attributable to precombination service |  |  |  |  |  |  |  |  |  | 138.0 |  |  |  |  |  |  |  |  |
Transaction costs |  |  |  |  |  |  |  |  |  | $ 95.0 |  |  |  |  |  |  |  |  |
Development Milestones | Themis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent consideration, maximum |  |  |  | 60.0 |  |  |  |  |  |  |  |  | 60.0 |  |  |  | 60.0 |  |
Regulatory Milestones | Themis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent consideration, maximum |  |  |  | 196.0 |  |  |  |  |  |  |  |  | 196.0 |  |  |  | 196.0 |  |
Sales-Based Milestones | Themis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent consideration, maximum |  |  |  | $ 194.0 |  |  |  |  |  |  |  |  | $ 194.0 |  |  |  | $ 194.0 |  |
Gilead Sciences | oral and injectable formulations programs | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit share by counterparty |  | 60.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit share |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gilead Sciences | oral formulation | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit share by counterparty |  | 65.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit share |  | 35.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales threshold |  | $ 2,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gilead Sciences | injectable formulation | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit share by counterparty |  | 65.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit share |  | 35.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales threshold |  | $ 3,500.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Artiva Biotherapeutics, Inc. | Licensing Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront and milestone payments |  |  | $ 30.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront and milestone payments to be made |  |  | $ 15.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Artiva Biotherapeutics, Inc. | Minimum | Licensing Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Royalty rate |  |  | 7.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Artiva Biotherapeutics, Inc. | Maximum | Licensing Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Royalty rate |  |  | 14.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Artiva Biotherapeutics, Inc. | Development Milestones | Licensing Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  | $ 217.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Artiva Biotherapeutics, Inc. | Regulatory Milestones | Licensing Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  | 570.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Artiva Biotherapeutics, Inc. | Sales-Based Milestones | Licensing Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  | $ 1,050.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Seagen |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 622.0 |  | $ 622.0 |  |  |
Upfront and milestone payments |  |  |  |  |  | 600.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  |  |  |  | 2,600.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Amount paid for investment |  |  |  |  |  | $ 1,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares acquired through equity investment | shares |  |  |  |  |  | 5 |  |  |  |  |  |  |  | 5 |  | 5 |  |  |
Share price (in dollars per share) | $ / shares |  |  |  |  |  | $ 200 |  |  |  |  |  |  |  | $ 200 |  | $ 200 |  |  |
Seagen | Tukysa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront and milestone payments |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 210.0 |  | $ 210.0 |  |  |
Seagen | Tukysa | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Royalty rate |  |  |  |  |  | 20.00% | 20.00% |  |  |  |  |  |  |  |  |  |  |  |
Seagen | Tukysa | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Royalty rate |  |  |  |  |  | 33.00% | 33.00% |  |  |  |  |  |  |  |  |  |  |  |
Seagen | Development Milestones |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  |  |  |  | $ 850.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Seagen | Regulatory Milestones | Tukysa |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  |  |  |  | 65.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Seagen | Sales-Based Milestones |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent milestone payments collaborative arrangement |  |  |  |  |  | $ 1,750.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Sentinel | Technology Rights |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life of acquired finite-lived intangible assets |  |  |  |  |  |  |  | 15 years |  |  |  |  |  |  |  |  |  |  |

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