Net Income Per Share Attributable to Gilead Common Shareholders - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Earnings Per Share [Abstract]
Net income attributable to Gilead	$ 3	$ 2,097	$ 1,817	$ 1,538	$ (3,865)	$ 2,718	$ 3,073	$ 2,702	$ 5,455	$ 4,628	$ 13,501
Shares used in per share calculation - basic									1,298	1,307	1,339
Stock options and equivalents									10	12	13
Conversion spread related to the Convertible Notes									0	0	2
Warrants related to the Convertible Notes									0	0	4
Shares used in per share calculation - diluted									1,308	1,319	1,358
Net income per share attributable to Gilead common stockholders - basic	$ 0.00	$ 1.62	$ 1.40	$ 1.18	$ (2.96)	$ 2.08	$ 2.35	$ 2.07	$ 4.20	$ 3.54	$ 10.08
Net income per share attributable to Gilead common stockholders - diluted	$ 0.00	$ 1.60	$ 1.39	$ 1.17	$ (2.96)	$ 2.06	$ 2.33	$ 2.05	$ 4.17	$ 3.51	$ 9.94