Selected Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2017	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
Quarterly Financial Data [Abstract]
Total revenues		$ 5,949	$ 6,512	$ 7,141	$ 6,505	$ 7,320	$ 7,500	$ 7,776	$ 7,794	$ 26,107	$ 30,390	$ 32,639
Gross profit on product sales		4,581	5,370	5,920	5,420	6,141	6,276	6,787	6,488
Net income		(3,836)	2,712	3,069	2,699	3,099	3,325	3,497	3,567	4,644	13,488	18,106
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
Net income per share attributable to Gilead common stockholders-basic (usd per share)		$ (2.96)	$ 2.08	$ 2.35	$ 2.07	$ 2.36	$ 2.52	$ 2.62	$ 2.58	$ 3.54	$ 10.08	$ 12.37
Earnings Per Share, Diluted		$ (2.96)	$ 2.06	$ 2.33	$ 2.05	$ 2.34	$ 2.49	$ 2.58	$ 2.53	$ 3.51	$ 9.94	$ 11.91
Estimated net charge related to enactment of TCJA	$ 5,500