INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) $ in Millions	Jun. 30, 2017 USD ($)
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	$ 85
Due after one year through five years	197
Due after 10 years	1,239
Total perpetual securities available for sale, amortized cost	1,521
Due in one year or less	82
Due after one year through five years	229
Due after 10 years	1,473
Total perpetual securities available for sale, fair value	1,784
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	59
Total perpetual securities available for sale, fair value	$ 59