Taxes on Income - Reconciliation Between Effective Tax Rate and US Statutory Rate (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Amount
U.S. statutory rate applied to income before taxes	$ 6,049		$ 1,941		$ 3,059
Differential arising from:
Foreign earnings	(1,486)		(1,316)		(1,955)
AstraZeneca option exercise	(774)		0		0
Sale of Sirna Therapeutics, Inc.	(357)		0		0
Tax settlements	(89)		(497)		(113)
The American Taxpayer Relief Act of 2012	0		(269)		0
Unremitted foreign earnings	(209)		(81)		(11)
Amortization of purchase accounting adjustments	865		934		905
Divestiture of Merck Consumer Care	440		0
Restructuring	289		224		62
U.S. health care reform legislation	134		65		60
Intangible asset impairment charges	148		56		40
Vioxx and ENHANCE litigation settlements	0		0		98
State taxes	7		44		31
Other	332	[1]	(73)	[1]	264	[1]
Taxes on income	$ 5,349		$ 1,028		$ 2,440
Tax Rate
U.S. statutory rate applied to income before taxes	35.00%		35.00%		35.00%
Differential arising from:
Foreign earnings	(8.60%)		(23.70%)		(22.40%)
AstraZeneca option exercise	(4.50%)		0.00%		0.00%
Sale of Sirna Therapeutics, Inc.	(2.10%)		0.00%		0.00%
Tax settlements	(0.50%)		(9.00%)		(1.30%)
The American Taxpayer Relief Act of 2012			(4.80%)
Unremitted foreign earnings	(1.20%)		(1.50%)		(0.10%)
Amortization of purchase accounting adjustments	5.00%		16.80%		10.30%
Divestiture of Merck Consumer Care	2.50%		0.00%		0.00%
Restructuring	1.70%		4.00%		0.70%
U.S. health care reform legislation	0.80%		1.20%		0.70%
Intangible asset impairment charges	0.90%		1.00%		0.50%
Vioxx and ENHANCE litigation settlements	0.00%		0.00%		1.20%
State taxes	0.00%		0.80%		0.30%
Other	1.90%	[1]	(1.30%)	[1]	3.00%	[1]
Total, Tax Rate	30.90%		18.50%		27.90%

[1] Other includes the tax effect of contingency reserves, research credits, tax rate changes and miscellaneous items.