Segment Information - Summary of Product Sales by Product (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment			1
Product Sales [Line Items]
Product sales	$ 6,402	$ 7,405	$ 19,825	$ 22,737
Total antiviral products
Product Sales [Line Items]
Product sales	5,843	6,841	18,123	21,150
Genvoya
Product Sales [Line Items]
Product sales	988	461	2,614	921
Harvoni
Product Sales [Line Items]
Product sales	973	1,860	3,726	7,441
Epclusa
Product Sales [Line Items]
Product sales	882	640	2,945	704
Truvada
Product Sales [Line Items]
Product sales	811	858	2,337	2,698
Atripla
Product Sales [Line Items]
Product sales	439	650	1,366	1,998
Descovy
Product Sales [Line Items]
Product sales	316	88	853	149
Odefsey
Product Sales [Line Items]
Product sales	296	105	781	174
Viread
Product Sales [Line Items]
Product sales	274	303	834	862
Complera/Eviplera
Product Sales [Line Items]
Product sales	237	411	744	1,160
Stribild
Product Sales [Line Items]
Product sales	229	621	831	1,527
Sovaldi
Product Sales [Line Items]
Product sales	219	825	847	3,460
Vosevi
Product Sales [Line Items]
Product sales	123	0	123	0
Other antiviral
Product Sales [Line Items]
Product sales	56	19	122	56
Letairis
Product Sales [Line Items]
Product sales	213	215	654	593
Ranexa
Product Sales [Line Items]
Product sales	164	170	517	467
AmBisome
Product Sales [Line Items]
Product sales	92	91	276	262
Zydelig
Product Sales [Line Items]
Product sales	40	39	110	129
Other
Product Sales [Line Items]
Product sales	$ 50	$ 49	$ 145	$ 136