Earnings Per Share - Calculations of Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Basic Earnings per Common Share
Net Income Attributable to Merck & Co., Inc.	$ 4,404		$ 6,168		$ 6,272
Less: Income allocated to participating securities	0		3		15
Net income allocated to common shareholders	4,404		6,165		6,257
Average common shares outstanding	2,963		3,041		3,071
Basic Earnings per Common Share	$ 1.49		$ 2.03		$ 2.04
Earnings per Common Share Assuming Dilution
Net Income Attributable to Merck & Co., Inc.	4,404		6,168		6,272
Less: Income allocated to participating securities	0		3		15
Net income allocated to common shareholders	$ 4,404		$ 6,165		$ 6,257
Average common shares outstanding	2,963		3,041		3,071
Common shares issuable	33	[1]	35	[1]	23	[1]
Average common shares outstanding assuming dilution	2,996		3,076		3,094
Diluted Earnings per Common Share	$ 1.47		$ 2.00		$ 2.02

[1] Issuable primarily under share-based compensation plans.