INCOME TAXES - Components of Income Tax Expense (Benefit) Applicable to Pretax Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Provision of Income Taxes [Line Items]
Current									$ 1,288	$ 1,079	$ 1,236
Deferred									41	461	422
Total income tax expense	$ 380	$ 297	$ 301	$ 350	$ 372	$ 368	$ 428	$ 372	1,329	1,540	1,658
Aflac U.S.
Reconciliation of Provision of Income Taxes [Line Items]
Current									225	84	302
Deferred									(1)	336	123
Total income tax expense									224	420	425
Aflac Japan
Reconciliation of Provision of Income Taxes [Line Items]
Current									1,063	995	934
Deferred									42	125	299
Total income tax expense									$ 1,105	$ 1,120	$ 1,233