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Acquisitions, Divestitures, Research Collaborations and Licensing Agreements - Narrative (Details) $ in Millions		1 Months Ended		2 Months Ended	3 Months Ended
	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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