Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 04, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized loss on investment of equity securities	$ 610,000,000	$ 1,700,000,000
Unrealized gain on investment of equity securities			$ 1,200,000,000
Other equity investments without readily determinable fair values	338,000,000	262,000,000
In-process research and development impairment	0	0	800,000,000
Kite Pharma, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
In-process research and development impairment			$ 800,000,000
Equity Securities Donation | Gilead Foundation
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Donation expense	212,000,000
Level 2 | MYR | Fair value, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability for MYR GmbH (“MYR”) contingent consideration	0	0
Level 3 | MYR | Fair value, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability for MYR GmbH (“MYR”) contingent consideration	317,000,000	0		$ 341,000,000
Fair value | MYR | Fair value, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability for MYR GmbH (“MYR”) contingent consideration	317,000,000	0
Fair value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term and long-term debt	28,600,000,000	34,600,000,000
Fair value | Level 3 | Immunomedics, Inc. | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Future royalties	1,300,000,000	1,100,000,000
Carrying value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term and long-term debt	25,600,000,000	30,300,000,000
Carrying value | Level 3 | Immunomedics, Inc. | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Future royalties	$ 1,100,000,000	$ 1,100,000,000