Revenues - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 6,577	$ 5,604	$ 17,268	$ 16,570
U.S.
Disaggregation of Revenue [Line Items]
Revenues	5,100	4,219	12,890	12,110
Europe
Disaggregation of Revenue [Line Items]
Revenues	937	871	2,698	2,908
Other International
Disaggregation of Revenue [Line Items]
Revenues	540	514	1,680	1,552
Atripla
Disaggregation of Revenue [Line Items]
Product revenues	113	149	311	472
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	99	132	275	387
Atripla | Europe
Disaggregation of Revenue [Line Items]
Product revenues	5	10	17	52
Atripla | Other International
Disaggregation of Revenue [Line Items]
Product revenues	9	7	19	33
Biktarvy
Disaggregation of Revenue [Line Items]
Product revenues	1,891	1,259	5,188	3,168
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	1,584	1,106	4,346	2,868
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Product revenues	194	108	528	229
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Product revenues	113	45	314	71
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Product revenues	70	93	218	331
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	26	40	77	126
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Product revenues	35	45	124	179
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Product revenues	9	8	17	26
Descovy
Disaggregation of Revenue [Line Items]
Product revenues	508	363	1,383	1,063
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	424	256	1,124	735
Descovy | Europe
Disaggregation of Revenue [Line Items]
Product revenues	49	63	156	200
Descovy | Other International
Disaggregation of Revenue [Line Items]
Product revenues	35	44	103	128
Genvoya
Disaggregation of Revenue [Line Items]
Product revenues	846	978	2,486	2,973
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	669	761	1,927	2,222
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Product revenues	116	152	376	522
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Product revenues	61	65	183	229
Odefsey
Disaggregation of Revenue [Line Items]
Product revenues	437	436	1,228	1,220
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	309	317	851	865
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Product revenues	116	111	341	328
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Product revenues	12	8	36	27
Stribild
Disaggregation of Revenue [Line Items]
Product revenues	42	94	154	298
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	27	63	100	208
Stribild | Europe
Disaggregation of Revenue [Line Items]
Product revenues	13	18	42	60
Stribild | Other International
Disaggregation of Revenue [Line Items]
Product revenues	2	13	12	30
Truvada
Disaggregation of Revenue [Line Items]
Product revenues	509	721	1,302	2,045
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	492	688	1,245	1,896
Truvada | Europe
Disaggregation of Revenue [Line Items]
Product revenues	6	14	20	88
Truvada | Other International
Disaggregation of Revenue [Line Items]
Product revenues	11	19	37	61
Other HIV
Disaggregation of Revenue [Line Items]
Product revenues	13	5	49	37
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	10	3	24	23
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Product revenues	1	1	4	3
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Product revenues	2	1	21	11
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Product revenues	118	104	362	254
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	82	68	244	165
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Product revenues	34	36	112	89
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Product revenues	2	0	6	0
AmBisome
Disaggregation of Revenue [Line Items]
Product revenues	111	99	325	297
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	18	9	46	27
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Product revenues	58	57	166	174
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Product revenues	35	33	113	96
Ledipasvir/Sofosbuvir
Disaggregation of Revenue [Line Items]
Product revenues	84	124	263	542
Ledipasvir/Sofosbuvir | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	36	54	113	257
Ledipasvir/Sofosbuvir | Europe
Disaggregation of Revenue [Line Items]
Product revenues	11	14	26	63
Ledipasvir/Sofosbuvir | Other International
Disaggregation of Revenue [Line Items]
Product revenues	37	56	124	222
Letairis
Disaggregation of Revenue [Line Items]
Product revenues	78	121	241	522
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	78	121	241	522
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	0	31	9	205
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	0	31	9	205
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	330	516	1,229	1,500
Sofosbuvir/Velpatasvir | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	170	282	646	731
Sofosbuvir/Velpatasvir | Europe
Disaggregation of Revenue [Line Items]
Product revenues	74	118	253	428
Sofosbuvir/Velpatasvir | Other International
Disaggregation of Revenue [Line Items]
Product revenues	86	116	330	341
Veklury
Disaggregation of Revenue [Line Items]
Product revenues	873	0	873	0
Veklury | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	785	0	785	0
Veklury | Europe
Disaggregation of Revenue [Line Items]
Product revenues	60	0	60	0
Veklury | Other International
Disaggregation of Revenue [Line Items]
Product revenues	28	0	28	0
Vemlidy
Disaggregation of Revenue [Line Items]
Product revenues	177	134	464	351
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	99	78	248	214
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Product revenues	8	6	22	15
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Product revenues	70	50	194	122
Viread
Disaggregation of Revenue [Line Items]
Product revenues	32	57	137	204
Viread | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	3	7	10	28
Viread | Europe
Disaggregation of Revenue [Line Items]
Product revenues	8	15	27	57
Viread | Other International
Disaggregation of Revenue [Line Items]
Product revenues	21	35	100	119
Vosevi
Disaggregation of Revenue [Line Items]
Product revenues	45	63	132	201
Vosevi | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	33	42	93	140
Vosevi | Europe
Disaggregation of Revenue [Line Items]
Product revenues	9	12	26	43
Vosevi | Other International
Disaggregation of Revenue [Line Items]
Product revenues	3	9	13	18
Yescarta
Disaggregation of Revenue [Line Items]
Product revenues	138	118	434	334
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	85	86	283	275
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Product revenues	51	32	144	59
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Product revenues	2	0	7	0
Zydelig
Disaggregation of Revenue [Line Items]
Product revenues	17	26	55	79
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	8	13	24	36
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Product revenues	9	13	30	42
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Product revenues	0	0	1	1
Other
Disaggregation of Revenue [Line Items]
Product revenues	61	25	184	227
Other | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	39	42	124	119
Other | Europe
Disaggregation of Revenue [Line Items]
Product revenues	20	(21)	54	96
Other | Other International
Disaggregation of Revenue [Line Items]
Product revenues	2	4	6	12
Total product sales
Disaggregation of Revenue [Line Items]
Product revenues	6,493	5,516	17,027	16,323
Revenues	6,493	5,516	17,027	16,323
Total product sales | U.S.
Disaggregation of Revenue [Line Items]
Product revenues	5,076	4,199	12,835	12,049
Total product sales | Europe
Disaggregation of Revenue [Line Items]
Product revenues	877	804	2,528	2,727
Total product sales | Other International
Disaggregation of Revenue [Line Items]
Product revenues	540	513	1,664	1,547
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Revenues	84	88	241	247
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Revenues	24	20	55	61
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues	60	67	170	181
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 1	$ 16	$ 5