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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income (loss) attributable to Gilead	$ (1,165)	$ 2,097	$ 2,690	$ 5,452
Shares used in per share calculation - basic (in shares)	1,267	1,296	1,271	1,302
Dilutive effect of stock options and equivalents (in shares)	0	11	7	11
Shares used in per share calculation - diluted (in shares)	1,267	1,307	1,278	1,313
Net income (loss) per share attributable to Gilead common stockholders - basic (usd per share)	$ (0.92)	$ 1.62	$ 2.12	$ 4.19
Net income (loss) per share attributable to Gilead common stockholders - diluted (usd per share)	$ (0.92)	$ 1.60	$ 2.10	$ 4.15