INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	$ 261
Due after one year through five years	449
Due after 10 years	1,340
Total perpetual securities available for sale, amortized cost	2,050
Due in one year or less	254
Due after one year through five years	453
Due after 10 years	1,401
Total perpetual securities available for sale, fair value	2,108
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	58
Total perpetual securities available for sale, fair value	$ 58