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INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail)
$ in Millions
Dec. 31, 2017
USD ($)
Aflac Japan  
Investments Classified by Economic Maturity Date [Line Items]  
Due after one year through five years $ 194
Due after 10 years 1,229
Total perpetual securities available for sale 1,423
Due after one year through five years 233
Due after 10 years 1,495
Total perpetual securities available for sale 1,728
Aflac U.S.  
Investments Classified by Economic Maturity Date [Line Items]  
Due after one year through five years 0
Due after 10 years 39
Total perpetual securities available for sale 39
Due after one year through five years 0
Due after 10 years 61
Total perpetual securities available for sale $ 61