CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income Attributable to Merck & Co., Inc.	$ 2,941	$ 1,901	$ 9,161	$ 7,487
Other Comprehensive Income (Loss) Net of Taxes:
Net unrealized (loss) gain on derivatives, net of reclassifications	(137)	91	(153)	(9)
Net unrealized (loss) gain on investments, net of reclassifications	0	(17)	(18)	109
Benefit plan net gain and prior service credit, net of amortization	62	15	161	41
Cumulative translation adjustment	85	(117)	(180)	14
Other comprehensive income (loss), net of taxes	10	(28)	(190)	155
Comprehensive Income Attributable to Merck & Co., Inc.	$ 2,951	$ 1,873	$ 8,971	$ 7,642