| Document and Entity Information Document | Sep. 10, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 10, 2020 |
| Entity Registrant Name | Quest Diagnostics Inc |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-12215 |
| Entity Tax Identification Number | 16-1387862 |
| Entity Address, Address Line One | 500 Plaza Drive |
| Entity Address, City or Town | Secaucus, |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07094 |
| City Area Code | (973) |
| Local Phone Number | 520-2700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 Par Value |
| Trading Symbol | DGX |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001022079 |
| Amendment Flag | false |
