CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net (Loss) Income Attributable to Merck & Co., Inc.	$ (56)	$ 2,184	$ 3,440	$ 4,515
Other Comprehensive Income (Loss) Net of Taxes:
Net unrealized loss on derivatives, net of reclassifications	(66)	(74)	(441)	(367)
Net unrealized gain (loss) on investments, net of reclassifications	135	(30)	213	96
Benefit plan net gain (loss) and prior service credit (cost), net of amortization	13	(144)	86	(280)
Cumulative translation adjustment	67	82	423	447
Other comprehensive income (loss), net of taxes	149	(166)	281	(104)
Comprehensive Income Attributable to Merck & Co., Inc.	$ 93	$ 2,018	$ 3,721	$ 4,411