Revenues - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Revenue	$ 5,088	$ 6,505
U.S.
Disaggregation Of Revenue [Line Items]
Revenue	3,547	4,469
Europe
Disaggregation Of Revenue [Line Items]
Revenue	1,057	1,359
Other International
Disaggregation Of Revenue [Line Items]
Revenue	484	677
Biktarvy
Disaggregation Of Revenue [Line Items]
Revenue	35	0
Biktarvy | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	35	0
Biktarvy | Europe
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Biktarvy | Other International
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Descovy
Disaggregation Of Revenue [Line Items]
Revenue	361	251
Descovy | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	274	209
Descovy | Europe
Disaggregation Of Revenue [Line Items]
Revenue	75	37
Descovy | Other International
Disaggregation Of Revenue [Line Items]
Revenue	12	5
Genvoya
Disaggregation Of Revenue [Line Items]
Revenue	1,082	769
Genvoya | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	853	669
Genvoya | Europe
Disaggregation Of Revenue [Line Items]
Revenue	186	87
Genvoya | Other International
Disaggregation Of Revenue [Line Items]
Revenue	43	13
Odefsey
Disaggregation Of Revenue [Line Items]
Revenue	342	227
Odefsey | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	279	203
Odefsey | Europe
Disaggregation Of Revenue [Line Items]
Revenue	58	23
Odefsey | Other International
Disaggregation Of Revenue [Line Items]
Revenue	5	1
Atripla
Disaggregation Of Revenue [Line Items]
Revenue	314	452
Atripla | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	228	316
Atripla | Europe
Disaggregation Of Revenue [Line Items]
Revenue	51	94
Atripla | Other International
Disaggregation Of Revenue [Line Items]
Revenue	35	42
Complera/Eviplera
Disaggregation Of Revenue [Line Items]
Revenue	190	253
Complera/Eviplera | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	67	112
Complera/Eviplera | Europe
Disaggregation Of Revenue [Line Items]
Revenue	109	125
Complera/Eviplera | Other International
Disaggregation Of Revenue [Line Items]
Revenue	14	16
Stribild
Disaggregation Of Revenue [Line Items]
Revenue	174	309
Stribild | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	133	226
Stribild | Europe
Disaggregation Of Revenue [Line Items]
Revenue	29	67
Stribild | Other International
Disaggregation Of Revenue [Line Items]
Revenue	12	16
Truvada
Disaggregation Of Revenue [Line Items]
Revenue	652	714
Truvada | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	507	464
Truvada | Europe
Disaggregation Of Revenue [Line Items]
Revenue	97	189
Truvada | Other International
Disaggregation Of Revenue [Line Items]
Revenue	48	61
Vemlidy
Disaggregation Of Revenue [Line Items]
Revenue	58	11
Vemlidy | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	47	11
Vemlidy | Europe
Disaggregation Of Revenue [Line Items]
Revenue	3	0
Vemlidy | Other International
Disaggregation Of Revenue [Line Items]
Revenue	8	0
Viread
Disaggregation Of Revenue [Line Items]
Revenue	97	260
Viread | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	7	117
Viread | Europe
Disaggregation Of Revenue [Line Items]
Revenue	30	71
Viread | Other International
Disaggregation Of Revenue [Line Items]
Revenue	60	72
Epclusa
Disaggregation Of Revenue [Line Items]
Revenue	536	892
Epclusa | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	269	735
Epclusa | Europe
Disaggregation Of Revenue [Line Items]
Revenue	198	138
Epclusa | Other International
Disaggregation Of Revenue [Line Items]
Revenue	69	19
Harvoni
Disaggregation Of Revenue [Line Items]
Revenue	348	1,371
Harvoni | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	234	926
Harvoni | Europe
Disaggregation Of Revenue [Line Items]
Revenue	56	243
Harvoni | Other International
Disaggregation Of Revenue [Line Items]
Revenue	58	202
Vosevi
Disaggregation Of Revenue [Line Items]
Revenue	107	0
Vosevi | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	86	0
Vosevi | Europe
Disaggregation Of Revenue [Line Items]
Revenue	16	0
Vosevi | Other International
Disaggregation Of Revenue [Line Items]
Revenue	5	0
Other antiviral
Disaggregation Of Revenue [Line Items]
Revenue	79	332
Other antiviral | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	4	41
Other antiviral | Europe
Disaggregation Of Revenue [Line Items]
Revenue	13	110
Other antiviral | Other International
Disaggregation Of Revenue [Line Items]
Revenue	62	181
Yescarta
Disaggregation Of Revenue [Line Items]
Revenue	40	0
Yescarta | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	40	0
Yescarta | Europe
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Yescarta | Other International
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Zydelig
Disaggregation Of Revenue [Line Items]
Revenue	33	35
Zydelig | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	14	15
Zydelig | Europe
Disaggregation Of Revenue [Line Items]
Revenue	18	19
Zydelig | Other International
Disaggregation Of Revenue [Line Items]
Revenue	1	1
Letairis
Disaggregation Of Revenue [Line Items]
Revenue	204	211
Letairis | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	204	211
Letairis | Europe
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Letairis | Other International
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Ranexa
Disaggregation Of Revenue [Line Items]
Revenue	195	153
Ranexa | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	195	153
Ranexa | Europe
Disaggregation Of Revenue [Line Items]
Revenue	0	0
Ranexa | Other International
Disaggregation Of Revenue [Line Items]
Revenue	0	0
AmBisome
Disaggregation Of Revenue [Line Items]
Revenue	107	92
AmBisome | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	17	9
AmBisome | Europe
Disaggregation Of Revenue [Line Items]
Revenue	56	52
AmBisome | Other International
Disaggregation Of Revenue [Line Items]
Revenue	34	31
Other
Disaggregation Of Revenue [Line Items]
Revenue	47	45
Other | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	34	33
Other | Europe
Disaggregation Of Revenue [Line Items]
Revenue	10	11
Other | Other International
Disaggregation Of Revenue [Line Items]
Revenue	3	1
Total product sales
Disaggregation Of Revenue [Line Items]
Revenue	5,001	6,377
Total product sales | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	3,527	4,450
Total product sales | Europe
Disaggregation Of Revenue [Line Items]
Revenue	1,005	1,266
Total product sales | Other International
Disaggregation Of Revenue [Line Items]
Revenue	469	661
Royalty, contract and other revenues
Disaggregation Of Revenue [Line Items]
Revenue	87	128
Royalty, contract and other revenues | U.S.
Disaggregation Of Revenue [Line Items]
Revenue	20	19
Royalty, contract and other revenues | Europe
Disaggregation Of Revenue [Line Items]
Revenue	52	93
Royalty, contract and other revenues | Other International
Disaggregation Of Revenue [Line Items]
Revenue	$ 15	$ 16