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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to Gilead	$ 360	$ (1,165)	$ (1,428)	$ 2,690
Shares used in per share calculation - basic (in shares)	1,255	1,267	1,257	1,271
Dilutive effect of stock options and equivalents (in shares)	6	0	0	7
Shares used in per share calculation - diluted (in shares)	1,261	1,267	1,257	1,278
Net income per share attributable to Gilead common stockholders - basic (usd per share)	$ 0.29	$ (0.92)	$ (1.14)	$ 2.12
Net income per share attributable to Gilead common stockholders - diluted (usd per share)	$ 0.29	$ (0.92)	$ (1.14)	$ 2.10