Selected Quarterly Financial Information (unaudited) Selected Quarterly Financial Information Narrative Details (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 [Line Items]
Up-front collaboration and licensing expenses related to Galapagos									$ 9,106	$ 5,018	$ 3,734
Income Tax Expense (Benefit)									(204)	2,339	8,885
Net gains from equity securities									(1,200)	(115)
Impairment charge related to IPR&D intangible asset	$ 800				$ 820				800	820	$ 0
Inventory write-downs									$ 649	$ 572
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
Upfront collaboration and licensing expense [Member]
Selected Quarterly Financial Information [Line Items]
Up-front collaboration and licensing expenses related to Galapagos		$ 3,920
Intangible Asset Transfer [Member]
Selected Quarterly Financial Information [Line Items]
Income Tax Expense (Benefit)	$ (1,200)				$ 588
Inventory write-downs for excess raw materials
Selected Quarterly Financial Information [Line Items]
Inventory write-downs	$ 500				$ 410				$ 547	$ 440
Upfront collaboration and licensing expense [Member]
Selected Quarterly Financial Information [Line Items]
Net income per share attributable to Gilead common stockholders - basic		$ 2.40
Net income per share attributable to Gilead common stockholders - diluted		$ 2.40
Unfavorable EPS Impact [Member]
Selected Quarterly Financial Information [Line Items]
Net income per share attributable to Gilead common stockholders - basic					$ (1.31)
Net income per share attributable to Gilead common stockholders - diluted					$ (1.30)
Favorable EPS Impact [Member]
Selected Quarterly Financial Information [Line Items]
Net income per share attributable to Gilead common stockholders - basic	$ 0.83
Net income per share attributable to Gilead common stockholders - diluted	$ 0.81
Intangible Asset Transfer [Member]
Selected Quarterly Financial Information [Line Items]
Net gains from equity securities	$ (929)