INCOME TAXES - Components of Income Tax Expense (Benefit) Applicable to Pretax Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Provision of Income Taxes [Line Items]
Current									$ 884	$ 1,288	$ 1,079
Deferred									524	41	461
Total income tax expense	$ 402	$ 334	$ 286	$ 386	$ 380	$ 297	$ 301	$ 350	1,408	1,329	1,540
Aflac U.S.
Reconciliation of Provision of Income Taxes [Line Items]
Current									234	225	84
Deferred									388	(1)	336
Total income tax expense									622	224	420
Aflac Japan
Reconciliation of Provision of Income Taxes [Line Items]
Current									650	1,063	995
Deferred									136	42	125
Total income tax expense									$ 786	$ 1,105	$ 1,120