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BUSINESS SEGMENT AND FOREIGN INFORMATION - Additional Information (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
segment
Dec. 31, 2019
USD ($)
Segment Reporting Information [Line Items]    
Number of reportable insurance business segments | segment 2  
Total receivables related to Aflac Japan's operations $ 796 $ 828
Aflac Japan    
Segment Reporting Information [Line Items]    
Total receivables related to Aflac Japan's operations $ 201 $ 258
Percentage of total receivables related to Aflac Japan's operations 25.20% 31.20%
Maximum | Machinery and equipment    
Segment Reporting Information [Line Items]    
Property, Plant and Equipment, Useful Life 20 years  
Maximum | Building    
Segment Reporting Information [Line Items]    
Property, Plant and Equipment, Useful Life 50 years  
Maximum | Furniture and fixtures    
Segment Reporting Information [Line Items]    
Property, Plant and Equipment, Useful Life 20 years