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INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail)
$ in Millions
Sep. 30, 2017
USD ($)
Aflac Japan  
Investments Classified by Economic Maturity Date [Line Items]  
Due in one year or less $ 84
Due after one year through five years 194
Due after 10 years 1,232
Total perpetual securities available for sale, amortized cost 1,510
Due in one year or less 85
Due after one year through five years 236
Due after 10 years 1,482
Total perpetual securities available for sale, fair value 1,803
Aflac U.S.  
Investments Classified by Economic Maturity Date [Line Items]  
Due in one year or less 0
Due after one year through five years 0
Due after 10 years 39
Total perpetual securities available for sale, amortized cost 39
Due in one year or less 0
Due after one year through five years 0
Due after 10 years 60
Total perpetual securities available for sale, fair value $ 60