Net Income 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
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income attributable to Gilead	$ 1,975	$ 1,538
Shares used in per share calculation - basic (in shares)	1,276	1,307
Dilutive effect of stock options and equivalents (in shares)	7	13
Shares used in per share calculation - diluted (in shares)	1,283	1,320
Net income per share attributable to Gilead common stockholders - basic (usd per share)	$ 1.55	$ 1.18
Net income per share attributable to Gilead common stockholders - diluted (usd per share)	$ 1.54	$ 1.17