Acquisitions, Research Collaborations and License Agreements (Details) - USD ($) $ in Millions		1 Months Ended				3 Months Ended		6 Months Ended		14 Months Ended	20 Months Ended
	Jan. 31, 2023	Jun. 30, 2023	Feb. 28, 2023	Jan. 31, 2023	May 31, 2022	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Research and development						$ 13,321	$ 2,798	$ 17,597	$ 5,374
Prometheus Biosciences, Inc.
Business Acquisition [Line Items]
Consideration transferred, asset acquisition		$ 11,000
Consideration transferred, to settle share-based equity awards		1,200
Consideration transferred, to settle equity awards, unvested		700
Net assets acquired		877
Cash recorded for asset acquisition		368
Investments recorded for asset acquisition		296
Deferred tax assets recorded for asset acquisition		218
Other net liabilities recorded for asset acquisition		$ 5
Research and development						$ 10,200		10,200
Imago Bio Sciences, Inc.
Business Acquisition [Line Items]
Consideration transferred, asset acquisition				$ 1,350
Net assets acquired	$ 219
Research and development								$ 1,200
Asset acquisition costs				60
Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Business Acquisition [Line Items]
Upfront and milestone payments made to collaborative partner			$ 175				$ 30		$ 30
Eligible future contingent development-related payments (up to)			1,000
Eligible future contingent regulatory milestone payments (up to)			2,800
Eligible future contingent sales-based milestone payments (up to)			$ 5,500
Preferred stock investment in counterparty	$ 100			$ 100
Milestone payments to be made to a collaborative partner					$ 30
Milestone payment to be made to a collaborative partner					25
Research and development payments made to a collaborative partner										$ 81
Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Development Milestones
Business Acquisition [Line Items]
Eligible future contingent development-related payments (up to)					90
Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | First Commercial Sale Milestones
Business Acquisition [Line Items]
Eligible future contingent sales-based milestone payments (up to)					290
Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Sales-Based Milestones
Business Acquisition [Line Items]
Eligible future contingent sales-based milestone payments (up to)					$ 780
Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Forecast
Business Acquisition [Line Items]
Research and development payments to be made to a collaborative partner											$ 111