CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income Attributable to Merck & Co., Inc.	$ 3,002	$ 2,670	$ 6,221	$ 5,585
Other Comprehensive (Loss) Income Net of Taxes:
Net unrealized loss on derivatives, net of reclassifications	(120)	(52)	(16)	(100)
Net unrealized gain (loss) on investments, net of reclassifications	0	44	(18)	126
Benefit plan net gain and prior service credit, net of amortization	39	11	99	26
Cumulative translation adjustment	79	(19)	(265)	131
Other comprehensive income (loss), net of taxes	(2)	(16)	(200)	183
Comprehensive Income Attributable to Merck & Co., Inc.	$ 3,000	$ 2,654	$ 6,021	$ 5,768