INVESTMENTS - Contractual Maturities of Investments in Fixed Maturities (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Held to maturity:
Total fixed maturities held to maturity, amortized cost	$ 31,998	$ 33,350
Held to maturity:
Total fixed maturities held to maturity, fair value	38,599	$ 40,021
Aflac Japan
Available for sale:
Due in one year or less	175
Due after one year through five years	5,734
Due after five years through 10 years	9,078
Due after 10 years	43,860
Mortgage- and asset-backed securities	290
Total fixed maturities available for sale, amortized cost	59,137
Held to maturity:
Due in one year or less	488
Due after one year through five years	923
Due after five years through 10 years	1,638
Due after 10 years	28,922
Mortgage- and asset-backed securities	27
Total fixed maturities held to maturity, amortized cost	31,998
Available for sale:
Due in one year or less	181
Due after one year through five years	6,029
Due after five years through 10 years	9,668
Due after 10 years	49,502
Mortgage- and asset-backed securities	330
Total fixed maturities available for sale, fair value	65,710
Held to maturity:
Due in one year or less	497
Due after one year through five years	970
Due after five years through 10 years	1,810
Due after 10 years	35,293
Mortgage- and asset-backed securities	29
Total fixed maturities held to maturity, fair value	38,599
Aflac U.S.
Available for sale:
Due in one year or less	53
Due after one year through five years	637
Due after five years through 10 years	3,253
Due after 10 years	8,443
Mortgage- and asset-backed securities	40
Total fixed maturities available for sale, amortized cost	12,426
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	54
Due after one year through five years	682
Due after five years through 10 years	3,529
Due after 10 years	9,698
Mortgage- and asset-backed securities	42
Total fixed maturities available for sale, fair value	14,005
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