Net Income Per Share Attributable to Gilead Common Shareholders - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to Gilead	$ (3,865)	$ 2,718	$ 3,073	$ 2,702	$ 3,108	$ 3,330	$ 3,497	$ 3,566	$ 4,628	$ 13,501	$ 18,108
Shares used in per share calculation - basic									1,307	1,339	1,464
Stock options and equivalents									12	13	23
Conversion spread related to the Convertible Notes									0	2	14
Warrants related to the Convertible Notes									0	4	20
Shares used in per share calculation - diluted									1,319	1,358	1,521
Net income per share attributable to Gilead common stockholders - basic	$ (2.96)	$ 2.08	$ 2.35	$ 2.07	$ 2.36	$ 2.52	$ 2.62	$ 2.58	$ 3.54	$ 10.08	$ 12.37
Net income per share attributable to Gilead common stockholders - diluted	$ (2.96)	$ 2.06	$ 2.33	$ 2.05	$ 2.34	$ 2.49	$ 2.58	$ 2.53	$ 3.51	$ 9.94	$ 11.91