| Cover | Feb. 04, 2025 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 04, 2025 |
| Entity File Number | 1-6571 |
| Entity Registrant Name | Merck & Co., Inc. |
| Entity Central Index Key | 0000310158 |
| Entity Tax Identification Number | 22-1918501 |
| Entity Incorporation, State or Country Code | NJ |
| 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 |
| City Area Code | 908 |
| Local Phone Number | 740-4000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock ($0.50 par value) |
| Trading Symbol | MRK |
| Security Exchange Name | NYSE |
| 1.875% Notes due 2026 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 1.875% Notes due 2026 |
| Trading Symbol | MRK/26 |
| Security Exchange Name | NYSE |
| 3.250% Notes due 2032 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 3.250% Notes due 2032 |
| Trading Symbol | MRK/32 |
| Security Exchange Name | NYSE |
| 2.500% Notes due 2034 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 2.500% Notes due 2034 |
| Trading Symbol | MRK/34 |
| Security Exchange Name | NYSE |
| 1.375% Notes due 2036 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 1.375% Notes due 2036 |
| Trading Symbol | MRK 36A |
| Security Exchange Name | NYSE |
| 3.500% Notes due 2037 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 3.500% Notes due 2037 |
| Trading Symbol | MRK/37 |
| Security Exchange Name | NYSE |
| 3.700% Notes due 2044 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 3.700% Notes due 2044 |
| Trading Symbol | MRK/44 |
| Security Exchange Name | NYSE |
| 3.750% Notes due 2054 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 3.750% Notes due 2054 |
| Trading Symbol | MRK/54 |
| Security Exchange Name | NYSE |
