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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to Gilead	$ 1,880	$ 1,817	$ 3,855	$ 3,355
Shares used in per share calculation - basic (in shares)	1,270	1,298	1,273	1,302
Dilutive effect of stock options and equivalents (in shares)	7	10	7	12
Shares used in per share calculation - diluted (in shares)	1,277	1,308	1,280	1,314
Net income per share attributable to Gilead common stockholders - basic (usd per share)	$ 1.48	$ 1.40	$ 3.03	$ 2.58
Net income per share attributable to Gilead common stockholders - diluted (usd per share)	$ 1.47	$ 1.39	$ 3.01	$ 2.55