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Document and Entity Information - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Jan. 31, 2018 | Jun. 30, 2017
Document And Entity Information [Abstract] |  |  |
Document Type | 10-K |  |
Amendment Flag | false |  |
Document Period End Date | Dec. 31, 2017 |  |
Document Fiscal Year Focus | 2017 |  |
Document Fiscal Period Focus | FY |  |
Trading Symbol | MRK |  |
Entity Registrant Name | Merck & Co., Inc. |  |
Entity Central Index Key | 0000310158 |  |
Current Fiscal Year End Date | --12-31 |  |
Entity Well-known Seasoned Issuer | Yes |  |
Entity Current Reporting Status | Yes |  |
Entity Voluntary Filers | No |  |
Entity Filer Category | Large Accelerated Filer |  |
Entity Common Stock, Shares Outstanding |  | 2,696,190,502 |
Entity Public Float |  |  | $ 174,700

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