DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Rollforward of Deferred Policy Acquisition Costs by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred policy acquisition costs:
Balance, beginning of year	$ 9,875
Capitalization	1,500	$ 1,500	$ 1,500
Amortization	(1,282)	(1,245)	(1,132)
Balance, end of year	10,128	9,875
Aflac Japan
Deferred policy acquisition costs:
Balance, beginning of year	6,384	6,150
Capitalization	825	833
Amortization	(709)	(710)	(630)
Foreign currency translation and other	84	111
Balance, end of year	6,584	6,384	6,150
Aflac U.S.
Deferred policy acquisition costs:
Balance, beginning of year	3,491	3,355
Capitalization	626	669
Amortization	(573)	(534)	(502)
Foreign currency translation and other	0	1
Balance, end of year	$ 3,544	$ 3,491	$ 3,355