| Document and Entity Information | Mar. 03, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | AFLAC INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000004977 |
| Document Type | 8-K |
| Document Period End Date | Mar. 3, 2021 |
| Entity Incorporation State Country Code | GA |
| Entity File Number | 001-07434 |
| Entity Tax Identification Number | 58-1167100 |
| Entity Address, Address Line One | 1932 Wynnton Road |
| Entity Address, City or Town | Columbus |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 31999 |
| City Area Code | 706 |
| Local Phone Number | 323.3431 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $.10 Par Value |
| Trading Symbol | AFL |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
