INVESTMENTS - Contractual Maturities of Investments in Fixed Maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Held to maturity:
Total fixed maturities held to maturity, amortized cost	$ 31,430	$ 33,350
Held to maturity:
Total fixed maturities held to maturity, fair value	38,072	$ 40,021
Aflac Japan
Available for sale:
Due in one year or less	234
Due after one year through five years	7,155
Due after five years through 10 years	7,812
Due after 10 years	45,028
Mortgage- and asset-backed securities	283
Total fixed maturities available for sale, amortized cost	60,512
Held to maturity:
Due in one year or less	885
Due after one year through five years	434
Due after five years through 10 years	1,634
Due after 10 years	28,451
Mortgage- and asset-backed securities	26
Total fixed maturities held to maturity, amortized cost	31,430
Available for sale:
Due in one year or less	243
Due after one year through five years	7,391
Due after five years through 10 years	8,385
Due after 10 years	51,269
Mortgage- and asset-backed securities	322
Total fixed maturities available for sale, fair value	67,610
Held to maturity:
Due in one year or less	903
Due after one year through five years	455
Due after five years through 10 years	1,802
Due after 10 years	34,885
Mortgage- and asset-backed securities	27
Total fixed maturities held to maturity, fair value	38,072
Aflac U.S.
Available for sale:
Due in one year or less	86
Due after one year through five years	508
Due after five years through 10 years	2,726
Due after 10 years	8,482
Mortgage- and asset-backed securities	40
Total fixed maturities available for sale, amortized cost	11,842
Held to maturity:
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	0
Mortgage- and asset-backed securities	0
Total fixed maturities held to maturity, amortized cost	0
Available for sale:
Due in one year or less	89
Due after one year through five years	542
Due after five years through 10 years	2,946
Due after 10 years	9,927
Mortgage- and asset-backed securities	41
Total fixed maturities available for sale, fair value	13,545
Held to maturity:
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	0
Mortgage- and asset-backed securities	0
Total fixed maturities held to maturity, fair value	$ 0