Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 5,685	$ 5,648	$ 10,966	$ 10,736
Revenues	5,685	5,648	10,966	10,736
U.S.
Disaggregation of Revenue [Line Items]
Revenues	4,073	4,083	7,891	7,630
Europe
Disaggregation of Revenue [Line Items]
Revenues	1,099	1,084	2,037	2,141
Other International
Disaggregation of Revenue [Line Items]
Revenues	513	481	1,038	965
Atripla
Disaggregation of Revenue [Line Items]
Revenues	152	349	323	663
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Revenues	122	274	255	502
Atripla | Europe
Disaggregation of Revenue [Line Items]
Revenues	26	39	42	90
Atripla | Other International
Disaggregation of Revenue [Line Items]
Revenues	4	36	26	71
Biktarvy
Disaggregation of Revenue [Line Items]
Revenues	1,116	185	1,909	220
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Revenues	1,023	183	1,762	218
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Revenues	73	2	121	2
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Revenues	20	0	26	0
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Revenues	123	199	238	389
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Revenues	42	82	86	149
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Revenues	72	103	134	212
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Revenues	9	14	18	28
Descovy
Disaggregation of Revenue [Line Items]
Revenues	358	403	700	764
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Revenues	246	311	479	585
Descovy | Europe
Disaggregation of Revenue [Line Items]
Revenues	69	78	137	153
Descovy | Other International
Disaggregation of Revenue [Line Items]
Revenues	43	14	84	26
Genvoya
Disaggregation of Revenue [Line Items]
Revenues	980	1,160	1,995	2,242
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Revenues	733	904	1,461	1,757
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Revenues	177	207	370	393
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Revenues	70	49	164	92
Odefsey
Disaggregation of Revenue [Line Items]
Revenues	387	385	784	727
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Revenues	266	303	548	582
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Revenues	111	77	217	135
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Revenues	10	5	19	10
Stribild
Disaggregation of Revenue [Line Items]
Revenues	108	187	204	361
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Revenues	78	144	145	277
Stribild | Europe
Disaggregation of Revenue [Line Items]
Revenues	24	34	42	63
Stribild | Other International
Disaggregation of Revenue [Line Items]
Revenues	6	9	17	21
Truvada
Disaggregation of Revenue [Line Items]
Revenues	718	765	1,324	1,417
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Revenues	657	649	1,208	1,156
Truvada | Europe
Disaggregation of Revenue [Line Items]
Revenues	41	86	74	183
Truvada | Other International
Disaggregation of Revenue [Line Items]
Revenues	20	30	42	78
Other HIV
Disaggregation of Revenue [Line Items]
Revenues	15	19	32	32
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Revenues	9	11	20	20
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Revenues	1	3	2	4
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Revenues	5	5	10	8
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Revenues	84	13	150	20
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Revenues	55	0	97	0
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Revenues	29	13	53	20
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
AmBisome
Disaggregation of Revenue [Line Items]
Revenues	105	103	198	210
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Revenues	10	14	18	31
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Revenues	60	55	117	111
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Revenues	35	34	63	68
Ledipasvir/Sofosbuvir
Disaggregation of Revenue [Line Items]
Revenues	193	331	418	679
Ledipasvir/Sofosbuvir | U.S.
Disaggregation of Revenue [Line Items]
Revenues	86	230	203	464
Ledipasvir/Sofosbuvir | Europe
Disaggregation of Revenue [Line Items]
Revenues	22	22	49	78
Ledipasvir/Sofosbuvir | Other International
Disaggregation of Revenue [Line Items]
Revenues	85	79	166	137
Letairis
Disaggregation of Revenue [Line Items]
Revenues	204	244	401	448
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Revenues	204	244	401	448
Letairis | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Letairis | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Ranexa
Disaggregation of Revenue [Line Items]
Revenues	19	208	174	403
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Revenues	19	208	174	403
Ranexa | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Ranexa | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Sofosbuvir/Velpatasvir
Disaggregation of Revenue [Line Items]
Revenues	493	500	984	1,036
Sofosbuvir/Velpatasvir | U.S.
Disaggregation of Revenue [Line Items]
Revenues	219	239	449	508
Sofosbuvir/Velpatasvir | Europe
Disaggregation of Revenue [Line Items]
Revenues	156	168	310	366
Sofosbuvir/Velpatasvir | Other International
Disaggregation of Revenue [Line Items]
Revenues	118	93	225	162
Vemlidy
Disaggregation of Revenue [Line Items]
Revenues	116	76	217	134
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Revenues	71	59	136	106
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Revenues	5	3	9	6
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Revenues	40	14	72	22
Viread
Disaggregation of Revenue [Line Items]
Revenues	75	82	147	179
Viread | U.S.
Disaggregation of Revenue [Line Items]
Revenues	9	16	21	23
Viread | Europe
Disaggregation of Revenue [Line Items]
Revenues	28	32	42	62
Viread | Other International
Disaggregation of Revenue [Line Items]
Revenues	38	34	84	94
Vosevi
Disaggregation of Revenue [Line Items]
Revenues	75	109	138	216
Vosevi | U.S.
Disaggregation of Revenue [Line Items]
Revenues	53	86	98	172
Vosevi | Europe
Disaggregation of Revenue [Line Items]
Revenues	15	20	31	36
Vosevi | Other International
Disaggregation of Revenue [Line Items]
Revenues	7	3	9	8
Yescarta
Disaggregation of Revenue [Line Items]
Revenues	120	68	216	108
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Revenues	99	68	189	108
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Revenues	21	0	27	0
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Zydelig
Disaggregation of Revenue [Line Items]
Revenues	26	39	53	72
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Revenues	12	17	23	31
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Revenues	14	22	29	40
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Revenues	0	0	1	1
Other(3)
Disaggregation of Revenue [Line Items]
Revenues	140	115	202	221
Other(3) | U.S.
Disaggregation of Revenue [Line Items]
Revenues	41	27	77	56
Other(3) | Europe
Disaggregation of Revenue [Line Items]
Revenues	97	41	117	56
Other(3) | Other International
Disaggregation of Revenue [Line Items]
Revenues	2	47	8	109
Product sales
Disaggregation of Revenue [Line Items]
Revenues	5,607	5,540	10,807	10,541
Product sales | U.S.
Disaggregation of Revenue [Line Items]
Revenues	4,054	4,069	7,850	7,596
Product sales | Europe
Disaggregation of Revenue [Line Items]
Revenues	1,041	1,005	1,923	2,010
Product sales | Other International
Disaggregation of Revenue [Line Items]
Revenues	512	466	1,034	935
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Revenues	78	108	159	195
Revenues	78	108	159	195
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Revenues	19	14	41	34
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues	58	79	114	131
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 1	$ 15	$ 4	$ 30