Equity - Shareholders' Equity (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended						9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Sep. 30, 2011 Common Stock [Member]	Dec. 31, 2010 Common Stock [Member]	Sep. 30, 2012 Other Paid-in Capital [Member]	Sep. 30, 2011 Other Paid-in Capital [Member]	Sep. 30, 2012 Retained Earnings [Member]	Sep. 30, 2011 Retained Earnings [Member]	Sep. 30, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Sep. 30, 2011 Accumulated Other Comprehensive Income (Loss) [Member]	Sep. 30, 2012 Treasury Stock [Member]	Sep. 30, 2011 Treasury Stock [Member]	Sep. 30, 2012 Noncontrolling Interest [Member]	Sep. 30, 2011 Noncontrolling Interest [Member]
Equity, Beginning Balance			$ 56,943	$ 56,805	$ 1,788	$ 1,788	$ 1,788	$ 1,788	$ 40,663	$ 40,701	$ 38,990	$ 37,536	$ (3,132)	$ (3,216)	$ (23,792)	$ (22,433)	$ 2,426	$ 2,429
Shares, Beginning Balance			3,577,103,522		3,577,000,000	3,577,000,000	3,577,000,000	3,577,000,000							536,000,000	495,000,000
Net Income Attributable to Merck & Co., Inc.	1,729	1,692	5,261	4,760							5,261	4,760
Cash dividends declared on common stock			(3,861)	(3,533)							(3,861)	(3,533)
Treasury stock shares purchased, shares															36,000,000	41,000,000
Treasury stock shares purchased			(1,439)	(1,359)											(1,439)	(1,359)
Share-based compensation plans and other, Shares															(39,000,000)	(11,000,000)
Share-based compensation plans and other			1,177	393					(192)	16					1,369	377
Other comprehensive income	86	63	92	503									92	503
Net income attributable to noncontrolling interests	34	32	89	89													89	89
Distributions attributable to noncontrolling interests			(50)	(62)													(50)	(62)
Equity, Ending Balance	$ 58,212	$ 57,596	$ 58,212	$ 57,596	$ 1,788	$ 1,788	$ 1,788	$ 1,788	$ 40,471	$ 40,717	$ 40,390	$ 38,763	$ (3,040)	$ (2,713)	$ (23,862)	$ (23,415)	$ 2,465	$ 2,456
Shares, Ending balance	3,577,103,522		3,577,103,522		3,577,000,000	3,577,000,000	3,577,000,000	3,577,000,000							533,000,000	525,000,000