Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues									$ 22,127	$ 26,107	$ 30,390
Revenues	$ 5,795	$ 5,596	$ 5,648	$ 5,088	$ 5,949	$ 6,512	$ 7,141	$ 6,505	22,127	26,107	30,390
U.S.
Disaggregation of Revenue [Line Items]
Revenues									16,269	18,194	19,354
Europe
Disaggregation of Revenue [Line Items]
Revenues									4,006	5,311	6,365
Other International
Disaggregation of Revenue [Line Items]
Revenues									1,852	2,602	4,671
Atripla
Disaggregation of Revenue [Line Items]
Revenues									1,206	1,806	2,605
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Revenues									967	1,288	1,898
Atripla | Europe
Disaggregation of Revenue [Line Items]
Revenues									131	335	520
Atripla | Other International
Disaggregation of Revenue [Line Items]
Revenues									108	183	187
Biktarvy
Disaggregation of Revenue [Line Items]
Revenues									1,184	0	0
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Revenues									1,144	0	0
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Revenues									39	0	0
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Revenues									1	0	0
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Revenues									653	966	1,457
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Revenues									276	406	821
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Revenues									327	503	580
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Revenues									50	57	56
Descovy
Disaggregation of Revenue [Line Items]
Revenues									1,581	1,218	298
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Revenues									1,217	958	226
Descovy | Europe
Disaggregation of Revenue [Line Items]
Revenues									308	226	69
Descovy | Other International
Disaggregation of Revenue [Line Items]
Revenues									56	34	3
Genvoya
Disaggregation of Revenue [Line Items]
Revenues									4,624	3,674	1,484
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Revenues									3,631	3,033	1,301
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Revenues									794	534	160
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Revenues									199	107	23
Odefsey
Disaggregation of Revenue [Line Items]
Revenues									1,598	1,106	329
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Revenues									1,242	964	302
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Revenues									335	132	27
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Revenues									21	10	0
Stribild
Disaggregation of Revenue [Line Items]
Revenues									644	1,053	1,914
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Revenues									505	811	1,523
Stribild | Europe
Disaggregation of Revenue [Line Items]
Revenues									97	195	314
Stribild | Other International
Disaggregation of Revenue [Line Items]
Revenues									42	47	77
Truvada
Disaggregation of Revenue [Line Items]
Revenues									2,997	3,134	3,566
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Revenues									2,605	2,266	2,384
Truvada | Europe
Disaggregation of Revenue [Line Items]
Revenues									260	644	913
Truvada | Other International
Disaggregation of Revenue [Line Items]
Revenues									132	224	269
Other HIV
Disaggregation of Revenue [Line Items]
Revenues									61	58	47
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Revenues									40	43	41
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Revenues									7	6	6
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Revenues									14	9	0
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Revenues									79	0	0
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Revenues									27	0	0
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Revenues									52	0	0
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
AmBisome
Disaggregation of Revenue [Line Items]
Revenues									420	366	356
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Revenues									46	28	20
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Revenues									229	207	209
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Revenues									145	131	127
Epclusa
Disaggregation of Revenue [Line Items]
Revenues									1,966	3,510	1,752
Epclusa | U.S.
Disaggregation of Revenue [Line Items]
Revenues									934	2,404	1,591
Epclusa | Europe
Disaggregation of Revenue [Line Items]
Revenues									654	869	141
Epclusa | Other International
Disaggregation of Revenue [Line Items]
Revenues									378	237	20
Harvoni
Disaggregation of Revenue [Line Items]
Revenues									1,222	4,370	9,081
Harvoni | U.S.
Disaggregation of Revenue [Line Items]
Revenues									802	3,053	4,941
Harvoni | Europe
Disaggregation of Revenue [Line Items]
Revenues									144	704	1,810
Harvoni | Other International
Disaggregation of Revenue [Line Items]
Revenues									276	613	2,330
Letairis
Disaggregation of Revenue [Line Items]
Revenues									943	887	819
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Revenues									943	887	819
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									758	717	677
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Revenues									758	717	677
Ranexa | Europe
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Ranexa | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Vemlidy
Disaggregation of Revenue [Line Items]
Revenues									321	122	3
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Revenues									245	111	3
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Revenues									12	5	0
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Revenues									64	6	0
Viread
Disaggregation of Revenue [Line Items]
Revenues									307	1,046	1,186
Viread | U.S.
Disaggregation of Revenue [Line Items]
Revenues									50	514	591
Viread | Europe
Disaggregation of Revenue [Line Items]
Revenues									82	238	302
Viread | Other International
Disaggregation of Revenue [Line Items]
Revenues									175	294	293
Vosevi
Disaggregation of Revenue [Line Items]
Revenues									396	293	0
Vosevi | U.S.
Disaggregation of Revenue [Line Items]
Revenues									304	267	0
Vosevi | Europe
Disaggregation of Revenue [Line Items]
Revenues									78	22	0
Vosevi | Other International
Disaggregation of Revenue [Line Items]
Revenues									14	4	0
Yescarta
Disaggregation of Revenue [Line Items]
Revenues									264	7	0
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Revenues									263	7	0
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Revenues									1	0	0
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Zydelig
Disaggregation of Revenue [Line Items]
Revenues									133	149	168
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Revenues									61	69	91
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Revenues									70	77	76
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Revenues									2	3	1
Other(3)
Disaggregation of Revenue [Line Items]
Revenues									320	1,180	4,211
Other(3) | U.S.
Disaggregation of Revenue [Line Items]
Revenues									137	283	2,036
Other(3) | Europe
Disaggregation of Revenue [Line Items]
Revenues									76	314	949
Other(3) | Other International
Disaggregation of Revenue [Line Items]
Revenues									107	583	1,226
Product sales
Disaggregation of Revenue [Line Items]
Revenues									21,677	25,662	29,953
Product sales | U.S.
Disaggregation of Revenue [Line Items]
Revenues									16,197	18,109	19,265
Product sales | Europe
Disaggregation of Revenue [Line Items]
Revenues									3,696	5,011	6,076
Product sales | Other International
Disaggregation of Revenue [Line Items]
Revenues									1,784	2,542	4,612
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Revenues									450	445	437
Revenues									450	445	437
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Revenues									72	85	89
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues									310	300	289
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Revenues									$ 68	$ 60	$ 59