Selected Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross profit on product sales	$ 4,111	$ 4,369	$ 4,344	$ 4,000	$ 4,581	$ 5,370	$ 5,920	$ 5,420
Net income	3	2,099	1,819	1,539	(3,836)	2,712	3,069	2,699	$ 5,460	$ 4,644	$ 13,488
Net income attributable to Gilead	$ 3	$ 2,097	$ 1,817	$ 1,538	$ (3,865)	$ 2,718	$ 3,073	$ 2,702	$ 5,455	$ 4,628	$ 13,501
Net income per share attributable to Gilead common stockholders-basic (usd per share)	$ 0.00	$ 1.62	$ 1.40	$ 1.18	$ (2.96)	$ 2.08	$ 2.35	$ 2.07	$ 4.20	$ 3.54	$ 10.08
Earnings Per Share, Diluted	$ 0.00	$ 1.60	$ 1.39	$ 1.17	$ (2.96)	$ 2.06	$ 2.33	$ 2.05	$ 4.17	$ 3.51	$ 9.94
Revenues	$ 5,795	$ 5,596	$ 5,648	$ 5,088	$ 5,949	$ 6,512	$ 7,141	$ 6,505	$ 22,127	$ 26,107	$ 30,390
Estimated net charge related to enactment of TCJA					$ 5,500
TCJAimpactBasicEPS					$ 4.20
TCJAImpactDilutedEPS					$ 4.16
ImpactBasicEPS	$ 1.31
ImpactDilutedEPS	$ 1.30
Impairment of Intangible Assets, Finite-lived	$ 820
Inventory write-down									572
impairmentTaxEffected [Member]
Finite-Lived Intangible Assets [Line Items]
Deferred Income Tax Expense (Benefit)	588
Inventory Reserve for Excess Raw Materials [Member]
Finite-Lived Intangible Assets [Line Items]
Inventory write-down	$ 410								$ 440