CONDENSED CONSOLIDATED STATEMENT OF INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Sales	$ 10,325	$ 10,536	$ 29,689	$ 29,692
Costs, Expenses and Other
Materials and production	3,274	3,409	9,369	10,559
Marketing and administrative	2,401	2,393	7,251	7,169
Research and development	4,383	1,664	7,927	5,475
Restructuring costs	153	161	470	386
Other (income) expense, net	(86)	22	30	88
Total Costs, Expenses and Other	10,125	7,649	25,047	23,677
Income Before Taxes	200	2,887	4,642	6,015
Taxes on Income	251	699	1,186	1,487
Net (Loss) Income	(51)	2,188	3,456	4,528
Less: Net Income Attributable to Noncontrolling Interests	5	4	16	13
Net (Loss) Income Attributable to Merck & Co., Inc.	$ (56)	$ 2,184	$ 3,440	$ 4,515
Basic (Loss) Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ (0.02)	$ 0.79	$ 1.26	$ 1.63
(Loss) Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	(0.02)	0.78	1.25	1.62
Dividends Declared per Common Share (in dollars per share)	$ 0.47	$ 0.46	$ 1.41	$ 1.38