Acquisitions, Divestitures, Research Collaborations and License Agreements - Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Business Combinations [Abstract]
Sales	$ 39,584	$ 43,437
Net income attributable to Merck & Co., Inc.	$ 4,640	$ 10,887
Basic earnings per common share attributable to Merck & Co., Inc. common shareholders (in dollars per share)	$ 1.65	$ 3.76
Earnings per common share assuming dilution attributable to Merck & Co. Inc. common shareholders (in dollars per share)	$ 1.63	$ 3.72

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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