Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 5,281	$ 5,088
Revenues	5,281	5,088
U.S.
Disaggregation of Revenue [Line Items]
Revenues	3,818	3,547
Europe
Disaggregation of Revenue [Line Items]
Revenues	938	1,057
Other International
Disaggregation of Revenue [Line Items]
Revenues	525	484
Atripla
Disaggregation of Revenue [Line Items]
Revenues	171	314
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Revenues	133	228
Atripla | Europe
Disaggregation of Revenue [Line Items]
Revenues	16	51
Atripla | Other International
Disaggregation of Revenue [Line Items]
Revenues	22	35
Biktarvy
Disaggregation of Revenue [Line Items]
Revenues	793	35
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Revenues	739	35
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Revenues	48	0
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Revenues	6	0
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Revenues	115	190
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Revenues	44	67
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Revenues	62	109
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Revenues	9	14
Descovy
Disaggregation of Revenue [Line Items]
Revenues	342	361
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Revenues	233	274
Descovy | Europe
Disaggregation of Revenue [Line Items]
Revenues	68	75
Descovy | Other International
Disaggregation of Revenue [Line Items]
Revenues	41	12
Genvoya
Disaggregation of Revenue [Line Items]
Revenues	1,015	1,082
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Revenues	728	853
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Revenues	193	186
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Revenues	94	43
Odefsey
Disaggregation of Revenue [Line Items]
Revenues	397	342
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Revenues	282	279
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Revenues	106	58
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Revenues	9	5
Stribild
Disaggregation of Revenue [Line Items]
Revenues	96	174
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Revenues	67	133
Stribild | Europe
Disaggregation of Revenue [Line Items]
Revenues	18	29
Stribild | Other International
Disaggregation of Revenue [Line Items]
Revenues	11	12
Truvada
Disaggregation of Revenue [Line Items]
Revenues	606	652
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Revenues	551	507
Truvada | Europe
Disaggregation of Revenue [Line Items]
Revenues	33	97
Truvada | Other International
Disaggregation of Revenue [Line Items]
Revenues	22	48
Other HIV
Disaggregation of Revenue [Line Items]
Revenues	17	13
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Revenues	11	9
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Revenues	1	1
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Revenues	5	3
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Revenues	66	7
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Revenues	42	0
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Revenues	24	7
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0
AmBisome
Disaggregation of Revenue [Line Items]
Revenues	93	107
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Revenues	8	17
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Revenues	57	56
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Revenues	28	34
Ledipasvir/Sofosbuvir
Disaggregation of Revenue [Line Items]
Revenues	225	348
Ledipasvir/Sofosbuvir | U.S.
Disaggregation of Revenue [Line Items]
Revenues	117	234
Ledipasvir/Sofosbuvir | Europe
Disaggregation of Revenue [Line Items]
Revenues	27	56
Ledipasvir/Sofosbuvir | Other International
Disaggregation of Revenue [Line Items]
Revenues	81	58
Letairis
Disaggregation of Revenue [Line Items]
Revenues	197	204
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Revenues	197	204
Letairis | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Letairis | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0
Ranexa
Disaggregation of Revenue [Line Items]
Revenues	155	195
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Revenues	155	195
Ranexa | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Ranexa | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0
Sofosbuvir/Velpatasvir
Disaggregation of Revenue [Line Items]
Revenues	491	536
Sofosbuvir/Velpatasvir | U.S.
Disaggregation of Revenue [Line Items]
Revenues	230	269
Sofosbuvir/Velpatasvir | Europe
Disaggregation of Revenue [Line Items]
Revenues	154	198
Sofosbuvir/Velpatasvir | Other International
Disaggregation of Revenue [Line Items]
Revenues	107	69
Vemlidy
Disaggregation of Revenue [Line Items]
Revenues	101	58
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Revenues	65	47
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Revenues	4	3
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Revenues	32	8
Viread
Disaggregation of Revenue [Line Items]
Revenues	72	97
Viread | U.S.
Disaggregation of Revenue [Line Items]
Revenues	12	7
Viread | Europe
Disaggregation of Revenue [Line Items]
Revenues	14	30
Viread | Other International
Disaggregation of Revenue [Line Items]
Revenues	46	60
Vosevi
Disaggregation of Revenue [Line Items]
Revenues	63	107
Vosevi | U.S.
Disaggregation of Revenue [Line Items]
Revenues	45	86
Vosevi | Europe
Disaggregation of Revenue [Line Items]
Revenues	16	16
Vosevi | Other International
Disaggregation of Revenue [Line Items]
Revenues	2	5
Yescarta
Disaggregation of Revenue [Line Items]
Revenues	96	40
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Revenues	90	40
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Revenues	6	0
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0
Zydelig
Disaggregation of Revenue [Line Items]
Revenues	27	33
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Revenues	11	14
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Revenues	15	18
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Revenues	1	1
Other(3)
Disaggregation of Revenue [Line Items]
Revenues	62	106
Other(3) | U.S.
Disaggregation of Revenue [Line Items]
Revenues	36	29
Other(3) | Europe
Disaggregation of Revenue [Line Items]
Revenues	20	15
Other(3) | Other International
Disaggregation of Revenue [Line Items]
Revenues	6	62
Product sales
Disaggregation of Revenue [Line Items]
Revenues	5,200	5,001
Product sales | U.S.
Disaggregation of Revenue [Line Items]
Revenues	3,796	3,527
Product sales | Europe
Disaggregation of Revenue [Line Items]
Revenues	882	1,005
Product sales | Other International
Disaggregation of Revenue [Line Items]
Revenues	522	469
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Revenues	81	87
Revenues	81	87
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Revenues	22	20
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues	56	52
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 3	$ 15