Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues									$ 22,449	$ 22,127	$ 26,107
Revenues	$ 5,879	$ 5,604	$ 5,685	$ 5,281	$ 5,795	$ 5,596	$ 5,648	$ 5,088	22,449	22,127	26,107
U.S.
Disaggregation of Revenue [Line Items]
Revenues									16,645	16,269	18,194
Europe
Disaggregation of Revenue [Line Items]
Revenues									3,811	4,006	5,311
Other International
Disaggregation of Revenue [Line Items]
Revenues									1,993	1,852	2,602
Atripla
Disaggregation of Revenue [Line Items]
Revenues									600	1,206	1,806
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Revenues									501	967	1,288
Atripla | Europe
Disaggregation of Revenue [Line Items]
Revenues									60	131	335
Atripla | Other International
Disaggregation of Revenue [Line Items]
Revenues									39	108	183
Biktarvy
Disaggregation of Revenue [Line Items]
Revenues									4,738	1,184	0
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Revenues									4,225	1,144	0
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Revenues									370	39	0
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Revenues									143	1	0
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Revenues									406	653	966
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Revenues									160	276	406
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Revenues									214	327	503
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Revenues									32	50	57
Descovy
Disaggregation of Revenue [Line Items]
Revenues									1,500	1,581	1,218
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Revenues									1,078	1,217	958
Descovy | Europe
Disaggregation of Revenue [Line Items]
Revenues									255	308	226
Descovy | Other International
Disaggregation of Revenue [Line Items]
Revenues									167	56	34
Genvoya
Disaggregation of Revenue [Line Items]
Revenues									3,931	4,624	3,674
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Revenues									2,984	3,631	3,033
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Revenues									664	794	534
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Revenues									283	199	107
Odefsey
Disaggregation of Revenue [Line Items]
Revenues									1,655	1,598	1,106
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Revenues									1,180	1,242	964
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Revenues									438	335	132
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Revenues									37	21	10
Stribild
Disaggregation of Revenue [Line Items]
Revenues									369	644	1,053
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Revenues									268	505	811
Stribild | Europe
Disaggregation of Revenue [Line Items]
Revenues									75	97	195
Stribild | Other International
Disaggregation of Revenue [Line Items]
Revenues									26	42	47
Truvada
Disaggregation of Revenue [Line Items]
Revenues									2,813	2,997	3,134
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Revenues									2,640	2,605	2,266
Truvada | Europe
Disaggregation of Revenue [Line Items]
Revenues									101	260	644
Truvada | Other International
Disaggregation of Revenue [Line Items]
Revenues									72	132	224
Other HIV
Disaggregation of Revenue [Line Items]
Revenues									47	61	58
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Revenues									30	40	43
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Revenues									5	7	6
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Revenues									12	14	9
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Revenues									379	79	0
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Revenues									249	27	0
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Revenues									130	52	0
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
AmBisome
Disaggregation of Revenue [Line Items]
Revenues									407	420	366
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Revenues									37	46	28
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Revenues									234	229	207
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Revenues									136	145	131
Ledipasvir/Sofosbuvir
Disaggregation of Revenue [Line Items]
Revenues									643	1,222	4,370
Ledipasvir/Sofosbuvir | U.S.
Disaggregation of Revenue [Line Items]
Revenues									312	802	3,053
Ledipasvir/Sofosbuvir | Europe
Disaggregation of Revenue [Line Items]
Revenues									71	144	704
Ledipasvir/Sofosbuvir | Other International
Disaggregation of Revenue [Line Items]
Revenues									260	276	613
Letairis
Disaggregation of Revenue [Line Items]
Revenues									618	943	887
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Revenues									618	943	887
Letairis | Europe
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Letairis | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Ranexa
Disaggregation of Revenue [Line Items]
Revenues									216	758	717
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Revenues									216	758	717
Ranexa | Europe
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Ranexa | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Sofosbuvir/Velpatasvir
Disaggregation of Revenue [Line Items]
Revenues									1,965	1,966	3,510
Sofosbuvir/Velpatasvir | U.S.
Disaggregation of Revenue [Line Items]
Revenues									971	934	2,404
Sofosbuvir/Velpatasvir | Europe
Disaggregation of Revenue [Line Items]
Revenues									553	654	869
Sofosbuvir/Velpatasvir | Other International
Disaggregation of Revenue [Line Items]
Revenues									441	378	237
Vemlidy
Disaggregation of Revenue [Line Items]
Revenues									488	321	122
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Revenues									309	245	111
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Revenues									21	12	5
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Revenues									158	64	6
Viread
Disaggregation of Revenue [Line Items]
Revenues									243	307	1,046
Viread | U.S.
Disaggregation of Revenue [Line Items]
Revenues									32	50	514
Viread | Europe
Disaggregation of Revenue [Line Items]
Revenues									69	82	238
Viread | Other International
Disaggregation of Revenue [Line Items]
Revenues									142	175	294
Vosevi
Disaggregation of Revenue [Line Items]
Revenues									257	396	293
Vosevi | U.S.
Disaggregation of Revenue [Line Items]
Revenues									178	304	267
Vosevi | Europe
Disaggregation of Revenue [Line Items]
Revenues									54	78	22
Vosevi | Other International
Disaggregation of Revenue [Line Items]
Revenues									25	14	4
Yescarta
Disaggregation of Revenue [Line Items]
Revenues									456	264	7
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Revenues									373	263	7
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Revenues									83	1	0
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Zydelig
Disaggregation of Revenue [Line Items]
Revenues									103	133	149
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Revenues									47	61	69
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Revenues									54	70	77
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Revenues									2	2	3
Other(3)
Disaggregation of Revenue [Line Items]
Revenues									285	320	1,180
Other(3) | U.S.
Disaggregation of Revenue [Line Items]
Revenues									157	137	283
Other(3) | Europe
Disaggregation of Revenue [Line Items]
Revenues									116	76	314
Other(3) | Other International
Disaggregation of Revenue [Line Items]
Revenues									12	107	583
Product sales
Disaggregation of Revenue [Line Items]
Revenues									22,119	21,677	25,662
Product sales | U.S.
Disaggregation of Revenue [Line Items]
Revenues									16,565	16,197	18,109
Product sales | Europe
Disaggregation of Revenue [Line Items]
Revenues									3,567	3,696	5,011
Product sales | Other International
Disaggregation of Revenue [Line Items]
Revenues									1,987	1,784	2,542
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Revenues									330	450	445
Revenues									330	450	445
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Revenues									80	72	85
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues									244	310	300
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Revenues									$ 6	$ 68	$ 60