DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Rollforward of Deferred Policy Acquisition Costs by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred policy acquisition costs:
Balance, beginning of year	$ 9,505
Capitalization	1,500	$ 1,500	$ 1,400
Amortization	(1,245)	(1,132)	(1,141)
Balance, end of year	9,875	9,505
Aflac Japan
Deferred policy acquisition costs:
Balance, beginning of year	6,150	5,765
Capitalization	833	839
Amortization	(710)	(630)	(644)
Foreign currency translation and other	111	176
Balance, end of year	6,384	6,150	5,765
Aflac U.S.
Deferred policy acquisition costs:
Balance, beginning of year	3,355	3,228
Capitalization	669	629
Amortization	(534)	(502)	(497)
Foreign currency translation and other	1	0
Balance, end of year	$ 3,491	$ 3,355	$ 3,228