Selected Quarterly Financial Information (unaudited) Selected Quarterly Financial Information Table (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Revenues	$ 5,879	$ 5,604	$ 5,685	$ 5,281	$ 5,795	$ 5,596	$ 5,648	$ 5,088	$ 22,449	$ 22,127	$ 26,107
Gross Profit	4,113	4,481	4,607	4,243	4,111	4,369	4,344	4,000
Net income	2,689	(1,168)	1,875	1,968	3	2,099	1,819	1,539	5,364	5,460	4,644
Net Income (Loss) Attributable to Parent	$ 2,696	$ (1,165)	$ 1,880	$ 1,975	$ 3	$ 2,097	$ 1,817	$ 1,538	$ 5,386	$ 5,455	$ 4,628
Net income per share attributable to Gilead common stockholders - basic	$ 2.13	$ (0.92)	$ 1.48	$ 1.55	$ 0	$ 1.62	$ 1.40	$ 1.18	$ 4.24	$ 4.20	$ 3.54
Net income per share attributable to Gilead common stockholders - diluted	$ 2.12	$ (0.92)	$ 1.47	$ 1.54	$ 0	$ 1.60	$ 1.39	$ 1.17	$ 4.22	$ 4.17	$ 3.51