Net Income (Loss) Per Share Attributable to Gilead Common Stockholders - Schedule of the Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to Gilead	$ (3,339)	$ 1,880	$ (1,788)	$ 3,855
Shares used in per share calculation - basic (in shares)	1,255	1,270	1,258	1,273
Dilutive effect of stock options and equivalents (in shares)	0	7	0	7
Shares used in per share calculation - diluted (in shares)	1,255	1,277	1,258	1,280
Net income per share attributable to Gilead common stockholders - basic (usd per share)	$ (2.66)	$ 1.48	$ (1.42)	$ 3.03
Net income per share attributable to Gilead common stockholders - diluted (usd per share)	$ (2.66)	$ 1.47	$ (1.42)	$ 3.01