DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Rollforward of Deferred Policy Acquisition Costs by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred policy acquisition costs:
Balance, beginning of year	$ 8,993
Capitalization	1,500	$ 1,400	$ 1,300
Amortization	(1,132)	(1,141)	(1,066)
Balance, end of year	9,505	8,993
Aflac Japan
Deferred policy acquisition costs:
Balance, beginning of year	5,765	5,370
Capitalization	839	864
Amortization	(630)	(644)	(578)
Foreign currency translation and other	176	175
Balance, end of year	6,150	5,765	5,370
Aflac U.S.
Deferred policy acquisition costs:
Balance, beginning of year	3,228	3,141
Capitalization	629	583
Amortization	(502)	(497)	(488)
Foreign currency translation and other	0	1
Balance, end of year	$ 3,355	$ 3,228	$ 3,141