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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to Gilead	$ 2,696	$ (1,165)	$ 1,880	$ 1,975	$ 3	$ 2,097	$ 1,817	$ 1,538	$ 5,386	$ 5,455	$ 4,628
Shares used in per share calculation - basic									1,270	1,298	1,307
Dilutive effect of stock options and equivalents									7	10	12
Shares used in per share calculation - diluted									1,277	1,308	1,319
Net income per share attributable to Gilead common stockholders - basic	$ 2.13	$ (0.92)	$ 1.48	$ 1.55	$ 0	$ 1.62	$ 1.40	$ 1.18	$ 4.24	$ 4.20	$ 3.54
Net income per share attributable to Gilead common stockholders - diluted	$ 2.12	$ (0.92)	$ 1.47	$ 1.54	$ 0	$ 1.60	$ 1.39	$ 1.17	$ 4.22	$ 4.17	$ 3.51