Revenues - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 5,143	$ 5,685	$ 10,691	$ 10,966
U.S.
Disaggregation of Revenue [Line Items]
Revenues	3,784	4,073	7,790	7,891
Europe
Disaggregation of Revenue [Line Items]
Revenues	786	1,099	1,761	2,037
Other International
Disaggregation of Revenue [Line Items]
Revenues	573	513	1,140	1,038
Atripla
Disaggregation of Revenue [Line Items]
Product revenues	103	152	198	323
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	95	122	176	255
Atripla | Europe
Disaggregation of Revenue [Line Items]
Product revenues	5	26	12	42
Atripla | Other International
Disaggregation of Revenue [Line Items]
Product revenues	3	4	10	26
Biktarvy
Disaggregation of Revenue [Line Items]
Product revenues	1,604	1,116	3,297	1,909
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	1,350	1,023	2,762	1,762
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Product revenues	153	73	334	121
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Product revenues	101	20	201	26
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Product revenues	72	123	148	238
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	27	42	51	86
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Product revenues	42	72	89	134
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Product revenues	3	9	8	18
Descovy
Disaggregation of Revenue [Line Items]
Product revenues	417	358	875	700
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	337	246	700	479
Descovy | Europe
Disaggregation of Revenue [Line Items]
Product revenues	46	69	107	137
Descovy | Other International
Disaggregation of Revenue [Line Items]
Product revenues	34	43	68	84
Genvoya
Disaggregation of Revenue [Line Items]
Product revenues	816	980	1,640	1,995
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	646	733	1,258	1,461
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Product revenues	109	177	260	370
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Product revenues	61	70	122	164
Odefsey
Disaggregation of Revenue [Line Items]
Product revenues	382	387	791	784
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	273	266	542	548
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Product revenues	98	111	225	217
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Product revenues	11	10	24	19
Stribild
Disaggregation of Revenue [Line Items]
Product revenues	59	108	112	204
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	39	78	73	145
Stribild | Europe
Disaggregation of Revenue [Line Items]
Product revenues	12	24	29	42
Stribild | Other International
Disaggregation of Revenue [Line Items]
Product revenues	8	6	10	17
Truvada
Disaggregation of Revenue [Line Items]
Product revenues	387	718	793	1,324
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	370	657	753	1,208
Truvada | Europe
Disaggregation of Revenue [Line Items]
Product revenues	6	41	14	74
Truvada | Other International
Disaggregation of Revenue [Line Items]
Product revenues	11	20	26	42
Other HIV
Disaggregation of Revenue [Line Items]
Product revenues	28	15	36	32
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	11	9	14	20
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Product revenues	1	1	3	2
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Product revenues	16	5	19	10
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Product revenues	132	84	244	150
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	90	55	162	97
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Product revenues	40	29	78	53
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Product revenues	2	0	4	0
AmBisome
Disaggregation of Revenue [Line Items]
Product revenues	95	105	214	198
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	10	10	28	18
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Product revenues	49	60	108	117
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Product revenues	36	35	78	63
Ledipasvir/Sofosbuvir
Disaggregation of Revenue [Line Items]
Product revenues	67	193	179	418
Ledipasvir/Sofosbuvir | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	24	86	77	203
Ledipasvir/Sofosbuvir | Europe
Disaggregation of Revenue [Line Items]
Product revenues	4	22	15	49
Ledipasvir/Sofosbuvir | Other International
Disaggregation of Revenue [Line Items]
Product revenues	39	85	87	166
Letairis
Disaggregation of Revenue [Line Items]
Product revenues	80	204	163	401
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	80	204	163	401
Letairis | Europe
Disaggregation of Revenue [Line Items]
Product revenues	0	0	0	0
Letairis | Other International
Disaggregation of Revenue [Line Items]
Product revenues	0	0	0	0
Ranexa
Disaggregation of Revenue [Line Items]
Product revenues	1	19	9	174
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	1	19	9	174
Ranexa | Europe
Disaggregation of Revenue [Line Items]
Product revenues	0	0	0	0
Ranexa | Other International
Disaggregation of Revenue [Line Items]
Product revenues	0	0	0	0
Sofosbuvir/Velpatasvir
Disaggregation of Revenue [Line Items]
Product revenues	335	493	899	984
Sofosbuvir/Velpatasvir | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	165	219	476	449
Sofosbuvir/Velpatasvir | Europe
Disaggregation of Revenue [Line Items]
Product revenues	57	156	179	310
Sofosbuvir/Velpatasvir | Other International
Disaggregation of Revenue [Line Items]
Product revenues	113	118	244	225
Vemlidy
Disaggregation of Revenue [Line Items]
Product revenues	151	116	287	217
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	76	71	149	136
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Product revenues	7	5	14	9
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Product revenues	68	40	124	72
Viread
Disaggregation of Revenue [Line Items]
Product revenues	65	75	105	147
Viread | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	3	9	7	21
Viread | Europe
Disaggregation of Revenue [Line Items]
Product revenues	8	28	19	42
Viread | Other International
Disaggregation of Revenue [Line Items]
Product revenues	54	38	79	84
Vosevi
Disaggregation of Revenue [Line Items]
Product revenues	39	75	87	138
Vosevi | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	27	53	60	98
Vosevi | Europe
Disaggregation of Revenue [Line Items]
Product revenues	6	15	17	31
Vosevi | Other International
Disaggregation of Revenue [Line Items]
Product revenues	6	7	10	9
Yescarta
Disaggregation of Revenue [Line Items]
Product revenues	156	120	296	216
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	95	99	198	189
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Product revenues	56	21	93	27
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Product revenues	5	0	5	0
Zydelig
Disaggregation of Revenue [Line Items]
Product revenues	18	26	38	53
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	8	12	16	23
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Product revenues	9	14	21	29
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Product revenues	1	0	1	1
Other
Disaggregation of Revenue [Line Items]
Product revenues	60	140	123	202
Other | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	43	41	85	77
Other | Europe
Disaggregation of Revenue [Line Items]
Product revenues	16	97	34	117
Other | Other International
Disaggregation of Revenue [Line Items]
Product revenues	1	2	4	8
Total product sales
Disaggregation of Revenue [Line Items]
Product revenues	5,067	5,607	10,534	10,807
Revenues	5,067	5,607	10,534	10,807
Total product sales | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	3,770	4,054	7,759	7,850
Total product sales | Europe
Disaggregation of Revenue [Line Items]
Product revenues	724	1,041	1,651	1,923
Total product sales | Other International
Disaggregation of Revenue [Line Items]
Product revenues	573	512	1,124	1,034
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Revenues	76	78	157	159
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Revenues	14	19	31	41
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues	62	58	110	114
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 1	$ 16	$ 4