INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) $ in Millions	Mar. 31, 2017 USD ($)
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	$ 90
Due after one year through five years	196
Due after 10 years	1,238
Total perpetual securities available for sale, amortized cost	1,524
Due in one year or less	87
Due after one year through five years	219
Due after 10 years	1,407
Total perpetual securities available for sale, fair value	1,713
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	57
Total perpetual securities available for sale, fair value	$ 57