REVENUES - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 6,217	$ 5,143	$ 12,640	$ 10,691
U.S.
Disaggregation of Revenue [Line Items]
Total revenues	4,233	3,784	8,493	7,790
Europe
Disaggregation of Revenue [Line Items]
Total revenues	1,192	786	2,528	1,761
Other International
Disaggregation of Revenue [Line Items]
Total revenues	792	573	1,619	1,140
Total product sales
Disaggregation of Revenue [Line Items]
Total revenues	6,152	5,067	12,492	10,534
Total product sales | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	4,213	3,770	8,453	7,759
Total product sales | Europe
Disaggregation of Revenue [Line Items]
Total revenues	1,147	724	2,422	1,651
Total product sales | Other International
Disaggregation of Revenue [Line Items]
Total revenues	792	573	1,617	1,124
Total HIV
Disaggregation of Revenue [Line Items]
Total revenues	3,938	4,000	7,588	8,134
Total HIV | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	3,044	3,238	5,830	6,491
Total HIV | Europe
Disaggregation of Revenue [Line Items]
Total revenues	596	512	1,174	1,151
Total HIV | Other International
Disaggregation of Revenue [Line Items]
Total revenues	298	250	584	492
Atripla
Disaggregation of Revenue [Line Items]
Total revenues	60	103	91	198
Atripla | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	52	95	75	176
Atripla | Europe
Disaggregation of Revenue [Line Items]
Total revenues	4	5	8	12
Atripla | Other International
Disaggregation of Revenue [Line Items]
Total revenues	4	3	8	10
Biktarvy
Disaggregation of Revenue [Line Items]
Total revenues	1,994	1,604	3,818	3,297
Biktarvy | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	1,586	1,350	3,051	2,762
Biktarvy | Europe
Disaggregation of Revenue [Line Items]
Total revenues	237	153	453	334
Biktarvy | Other International
Disaggregation of Revenue [Line Items]
Total revenues	171	101	314	201
Complera/Eviplera
Disaggregation of Revenue [Line Items]
Total revenues	62	72	125	148
Complera/Eviplera | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	20	27	45	51
Complera/Eviplera | Europe
Disaggregation of Revenue [Line Items]
Total revenues	39	42	73	89
Complera/Eviplera | Other International
Disaggregation of Revenue [Line Items]
Total revenues	3	3	7	8
Descovy
Disaggregation of Revenue [Line Items]
Total revenues	435	417	794	875
Descovy | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	357	337	639	700
Descovy | Europe
Disaggregation of Revenue [Line Items]
Total revenues	44	46	86	107
Descovy | Other International
Disaggregation of Revenue [Line Items]
Total revenues	34	34	69	68
Genvoya
Disaggregation of Revenue [Line Items]
Total revenues	706	816	1,379	1,640
Genvoya | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	551	646	1,057	1,258
Genvoya | Europe
Disaggregation of Revenue [Line Items]
Total revenues	100	109	206	260
Genvoya | Other International
Disaggregation of Revenue [Line Items]
Total revenues	55	61	116	122
Odefsey
Disaggregation of Revenue [Line Items]
Total revenues	382	382	749	791
Odefsey | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	258	273	498	542
Odefsey | Europe
Disaggregation of Revenue [Line Items]
Total revenues	111	98	224	225
Odefsey | Other International
Disaggregation of Revenue [Line Items]
Total revenues	13	11	27	24
Stribild
Disaggregation of Revenue [Line Items]
Total revenues	51	59	97	112
Stribild | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	35	39	66	73
Stribild | Europe
Disaggregation of Revenue [Line Items]
Total revenues	11	12	22	29
Stribild | Other International
Disaggregation of Revenue [Line Items]
Total revenues	5	8	9	10
Truvada
Disaggregation of Revenue [Line Items]
Total revenues	108	387	243	793
Truvada | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	94	370	213	753
Truvada | Europe
Disaggregation of Revenue [Line Items]
Total revenues	6	6	13	14
Truvada | Other International
Disaggregation of Revenue [Line Items]
Total revenues	8	11	17	26
Other HIV
Disaggregation of Revenue [Line Items]
Total revenues	11	28	28	36
Other HIV | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	5	11	11	14
Other HIV | Europe
Disaggregation of Revenue [Line Items]
Total revenues	4	1	5	3
Other HIV | Other International
Disaggregation of Revenue [Line Items]
Total revenues	2	16	12	19
Revenue share - Symtuza
Disaggregation of Revenue [Line Items]
Total revenues	129	132	264	244
Revenue share - Symtuza | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	86	90	175	162
Revenue share - Symtuza | Europe
Disaggregation of Revenue [Line Items]
Total revenues	40	40	84	78
Revenue share - Symtuza | Other International
Disaggregation of Revenue [Line Items]
Total revenues	3	2	5	4
Total HCV
Disaggregation of Revenue [Line Items]
Total revenues	549	448	1,059	1,177
Total HCV | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	327	220	585	618
Total HCV | Europe
Disaggregation of Revenue [Line Items]
Total revenues	93	70	228	218
Total HCV | Other International
Disaggregation of Revenue [Line Items]
Total revenues	129	158	246	341
Ledipasvir/Sofosbuvir
Disaggregation of Revenue [Line Items]
Total revenues	62	67	118	179
Ledipasvir/Sofosbuvir | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	30	24	49	77
Ledipasvir/Sofosbuvir | Europe
Disaggregation of Revenue [Line Items]
Total revenues	3	4	19	15
Ledipasvir/Sofosbuvir | Other International
Disaggregation of Revenue [Line Items]
Total revenues	29	39	50	87
Sofosbuvir/Velpatasvir
Disaggregation of Revenue [Line Items]
Total revenues	442	335	823	899
Sofosbuvir/Velpatasvir | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	262	165	476	476
Sofosbuvir/Velpatasvir | Europe
Disaggregation of Revenue [Line Items]
Total revenues	82	57	157	179
Sofosbuvir/Velpatasvir | Other International
Disaggregation of Revenue [Line Items]
Total revenues	98	113	190	244
Other HCV
Disaggregation of Revenue [Line Items]
Total revenues	45	46	118	99
Other HCV | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	35	31	60	65
Other HCV | Europe
Disaggregation of Revenue [Line Items]
Total revenues	8	9	52	24
Other HCV | Other International
Disaggregation of Revenue [Line Items]
Total revenues	2	6	6	10
Total HBV/HDV
Disaggregation of Revenue [Line Items]
Total revenues	237	219	457	405
Total HBV/HDV | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	90	80	171	165
Total HBV/HDV | Europe
Disaggregation of Revenue [Line Items]
Total revenues	24	17	47	37
Total HBV/HDV | Other International
Disaggregation of Revenue [Line Items]
Total revenues	123	122	239	203
Vemlidy
Disaggregation of Revenue [Line Items]
Total revenues	200	151	381	287
Vemlidy | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	86	76	163	149
Vemlidy | Europe
Disaggregation of Revenue [Line Items]
Total revenues	8	7	16	14
Vemlidy | Other International
Disaggregation of Revenue [Line Items]
Total revenues	106	68	202	124
Viread
Disaggregation of Revenue [Line Items]
Total revenues	28	65	59	105
Viread | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	3	3	7	7
Viread | Europe
Disaggregation of Revenue [Line Items]
Total revenues	8	8	15	19
Viread | Other International
Disaggregation of Revenue [Line Items]
Total revenues	17	54	37	79
Other HBV/HBD
Disaggregation of Revenue [Line Items]
Total revenues	9	3	17	13
Other HBV/HBD | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	1	1	1	9
Other HBV/HBD | Europe
Disaggregation of Revenue [Line Items]
Total revenues	8	2	16	4
Other HBV/HBD | Other International
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Veklury
Disaggregation of Revenue [Line Items]
Total revenues	829	0	2,285	0
Veklury | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	416	0	1,236	0
Veklury | Europe
Disaggregation of Revenue [Line Items]
Total revenues	264	0	652	0
Veklury | Other International
Disaggregation of Revenue [Line Items]
Total revenues	149	0	397	0
Total Cell Therapy
Disaggregation of Revenue [Line Items]
Total revenues	219	157	410	297
Total Cell Therapy | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	140	95	259	198
Total Cell Therapy | Europe
Disaggregation of Revenue [Line Items]
Total revenues	70	57	135	94
Total Cell Therapy | Other International
Disaggregation of Revenue [Line Items]
Total revenues	9	5	16	5
Tecartus
Disaggregation of Revenue [Line Items]
Total revenues	41	1	72	1
Tecartus | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	32	0	59	0
Tecartus | Europe
Disaggregation of Revenue [Line Items]
Total revenues	9	1	13	1
Tecartus | Other International
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Yescarta
Disaggregation of Revenue [Line Items]
Total revenues	178	156	338	296
Yescarta | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	108	95	200	198
Yescarta | Europe
Disaggregation of Revenue [Line Items]
Total revenues	61	56	122	93
Yescarta | Other International
Disaggregation of Revenue [Line Items]
Total revenues	9	5	16	5
Trodelvy
Disaggregation of Revenue [Line Items]
Total revenues	89	0	161	0
Trodelvy | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	89	0	161	0
Trodelvy | Europe
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Trodelvy | Other International
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Total Other
Disaggregation of Revenue [Line Items]
Total revenues	291	243	532	521
Total Other | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	107	137	211	287
Total Other | Europe
Disaggregation of Revenue [Line Items]
Total revenues	100	68	186	151
Total Other | Other International
Disaggregation of Revenue [Line Items]
Total revenues	84	38	135	83
AmBisome
Disaggregation of Revenue [Line Items]
Total revenues	156	95	277	214
AmBisome | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	13	10	25	28
AmBisome | Europe
Disaggregation of Revenue [Line Items]
Total revenues	69	49	135	108
AmBisome | Other International
Disaggregation of Revenue [Line Items]
Total revenues	74	36	117	78
Letairis
Disaggregation of Revenue [Line Items]
Total revenues	57	80	111	163
Letairis | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	57	80	111	163
Letairis | Europe
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Letairis | Other International
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Ranexa
Disaggregation of Revenue [Line Items]
Total revenues	2	1	5	9
Ranexa | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	2	1	5	9
Ranexa | Europe
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Ranexa | Other International
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Zydelig
Disaggregation of Revenue [Line Items]
Total revenues	22	18	37	38
Zydelig | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	8	8	16	16
Zydelig | Europe
Disaggregation of Revenue [Line Items]
Total revenues	13	9	20	21
Zydelig | Other International
Disaggregation of Revenue [Line Items]
Total revenues	1	1	1	1
Other
Disaggregation of Revenue [Line Items]
Total revenues	54	49	102	97
Other | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	27	38	54	71
Other | Europe
Disaggregation of Revenue [Line Items]
Total revenues	18	10	31	22
Other | Other International
Disaggregation of Revenue [Line Items]
Total revenues	9	1	17	4
Royalty, contract and other revenues
Disaggregation of Revenue [Line Items]
Total revenues	65	76	148	157
Royalty, contract and other revenues | U.S.
Disaggregation of Revenue [Line Items]
Total revenues	20	14	40	31
Royalty, contract and other revenues | Europe
Disaggregation of Revenue [Line Items]
Total revenues	45	62	106	110
Royalty, contract and other revenues | Other International
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 0	$ 2	$ 16