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Cover - USD ($)
 12 Months Ended
Dec. 31, 2023
Jan. 31, 2024
Jun. 30, 2023
Document Information [Line Items]      
Document Type 10-K/A    
Document Annual Report true    
Document Transition Report false    
ICFR Auditor Attestation Flag true    
Amendment Flag true    
Amendment Description Merck & Co., Inc. (the “Company”) filed its Annual Report on Form 10-K for the fiscal year ended December 31, 2023 (the “Original Form 10-K”) with the Securities and Exchange Commission on February 26, 2024. The Company is filing this Amendment No. 1 (this “Amendment”) to the Original Form 10-K solely to correct the date of the Annual Meeting of Shareholders. In the Original Form 10-K, that date was inadvertently referenced as May 18, 2024. The date of the Annual Meeting of Shareholders is May 28, 2024. Accordingly, this Amendment is being filed solely to:     •   amend Part III, Items 10, 11, 12, 13 and 14 of the Original Form 10-K to correct the date of the Annual Meeting of Shareholders;     •   correct the date of the Annual Meeting of Shareholders on the cover of the filing; and     •   file new certifications of our principal executive officer and principal financial officer as exhibits to this Amendment under Item 15 of Part IV hereof pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended, and pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. This Amendment does not reflect any events occurring after the filing of the Original Form 10-K or modify or update the disclosure contained therein in any way other than as required to reflect the correction discussed above. Accordingly, this Amendment should be read in conjunction with the Original Form 10-K.    
Document Period End Date Dec. 31, 2023    
Entity Registrant Name Merck & Co., Inc.    
Entity Central Index Key 0000310158    
Entity File Number 1-6571    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Shell Company false    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Public Float     $ 292,929,000,000
Entity Address, Address Line One 126 East Lincoln Avenue    
Entity Address, City or Town Rahway    
Entity Address, State or Province NJ    
Entity Address, Postal Zip Code 07065    
Title of 12(b) Security Common Stock ($0.50 par value)    
Trading Symbol MRK    
Security Exchange Name NYSE    
City Area Code 908    
Local Phone Number 740-4000    
Entity Incorporation, State or Country Code NJ    
Entity Tax Identification Number 22-1918501    
Entity Interactive Data Current Yes    
Document Financial Statement Error Correction [Flag] false    
Entity Common Stock, Shares Outstanding   2,532,643,872  
Documents Incorporated by Reference [Text Block] Proxy Statement for the Annual Meeting of Shareholders to be held May 28, 2024, to be filed with the Securities and Exchange Commission within 120 days after the close of the fiscal year covered by this report    
Document Fiscal Year Focus 2023    
Document Fiscal Period Focus FY    
A 0.500 Notes due 2024 [Member]      
Document Information [Line Items]      
Title of 12(b) Security 0.500% Notes due 2024    
Trading Symbol MRK 24    
Security Exchange Name NYSE    
A 1.875 Notes due 2026 [Member]      
Document Information [Line Items]      
Title of 12(b) Security 1.875% Notes due 2026    
Trading Symbol MRK/26    
Security Exchange Name NYSE    
A 2.500 Notes due 2034 [Member]      
Document Information [Line Items]      
Title of 12(b) Security 2.500% Notes due 2034    
Trading Symbol MRK/34    
Security Exchange Name NYSE    
A 1.375 Notes due 2036 [Member]      
Document Information [Line Items]      
Title of 12(b) Security 1.375% Notes due 2036    
Trading Symbol MRK 36A    
Security Exchange Name NYSE