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Acquisitions, Divestitures, Research Collaborations and Licensing Agreements - Narrative (Details) $ in Millions |  | 1 Months Ended | 2 Months Ended | 3 Months Ended |  |  |
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Jun. 02, 2021 | Mar. 31, 2024 USD ($) jurisdiction | Jan. 31, 2023 USD ($) | Jul. 31, 2024 USD ($) | Mar. 31, 2024 USD ($) jurisdiction | Mar. 31, 2023 USD ($) | Dec. 31, 2023 USD ($) | Oct. 31, 2023 USD ($) candidate | Feb. 28, 2023 candidate
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  | $ 3,992 | $ 4,276 |  |  |
Sales |  |  |  |  | 15,775 | 14,487 |  |  |
Cost of sales |  |  |  |  | 3,540 | 3,926 |  |  |
Other current assets |  | $ 7,950 |  |  | 7,950 |  | $ 8,368 |  |
Accrued and other current liabilities |  | 14,102 |  |  | 14,102 |  | 15,766 |  |
Related Party |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Other current assets |  | 462 |  |  | 462 |  | 632 |  |
Accrued and other current liabilities |  | $ 193 |  |  | 193 |  | $ 598 |  |
Manufacturing and Supply Agreements | Related Party |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Sales |  |  |  |  | 107 | 94 |  |  |
Cost of sales |  |  |  |  | $ 110 | 107 |  |  |
Minimum | Manufacturing and Supply Agreements | Related Party |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Period of continuing involvement after disposal | 4 years |  |  |  |  |  |  |  |
Maximum | Manufacturing and Supply Agreements | Related Party |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Period of continuing involvement after disposal | 10 years |  |  |  |  |  |  |  |
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Organon & Co. |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Number of jurisdictions remaining | jurisdiction |  | 1 |  |  | 1 |  |  |  |
Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Number of antibody drug conjugates obtained right and obligations | candidate |  |  |  |  |  |  |  |  | 7
Upfront payment made to collaborative partner |  |  |  |  |  | 175 |  |  |
Number of antibody drug conjugates terminated with collaborative partner | candidate |  |  |  |  |  |  |  | 2 |
Eligible future contingent development-related payments (up to) |  |  |  |  |  |  |  | $ 600 |
Eligible future contingent regulatory milestone payments (up to) |  |  |  |  |  |  |  | 1,600 |
Eligible future contingent sales-based milestone payments (up to) |  |  |  |  |  |  |  | $ 3,100 |
Stock investment in counterparty |  |  | $ 100 |  |  |  |  |  |
Elanco Animal Health Incorporated Aqua Business | Forecast |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Payment to acquire business |  |  |  | $ 1,300 |  |  |  |  |
Harpoon Therapeutics, Inc. |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Consideration transferred, asset acquisition |  | $ 765 |  |  |  |  |  |  |
Asset acquisition, transaction costs |  | 56 |  |  |  |  |  |  |
Net assets acquired |  | $ 165 |  |  |  |  |  |  |
Research and development |  |  |  |  | $ 656 |  |  |  |
Imago Bio Sciences, Inc. |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Consideration transferred, asset acquisition |  |  | 1,350 |  |  |  |  |  |
Asset acquisition, transaction costs |  |  | 60 |  |  |  |  |  |
Net assets acquired |  |  | $ 219 |  |  |  |  |  |
Research and development |  |  |  |  |  | $ 1,200 |  |  |

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