| Document and Entity Information | Sep. 11, 2019 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0000005513 |
| Document Type | 8-K |
| Document Period End Date | Sep. 11, 2019 |
| Entity Registrant Name | UNUM GROUP |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-11294 |
| Entity Tax Identification Number | 62-1598430 |
| Entity Address, Address Line One | 1 Fountain Square |
| Entity Address, City or Town | Chattanooga |
| Entity Address, State or Province | TN |
| Entity Address, Postal Zip Code | 37402 |
| City Area Code | (423) |
| Local Phone Number | 294-1011 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common stock, $0.10 par value |
| Trading Symbol | UNM |
| Security Exchange Name | NYSE |
| Junior Notes [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 6.250% Junior Subordinated Notes due 2058 |
| Trading Symbol | UNMA |
| Security Exchange Name | NYSE |
