DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Rollforward of Deferred Policy Acquisition Costs by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred policy acquisition costs:
Balance, beginning of year	$ 10,128
Capitalization	1,200	$ 1,500	$ 1,500
Amortization	(1,214)	(1,282)	(1,245)
Balance, end of year	10,441	10,128
Aflac Japan
Deferred policy acquisition costs:
Balance, beginning of year	6,584	6,384
Capitalization	665	825
Amortization	(644)	(709)	(710)
Foreign currency translation and other	386	84
Balance, end of year	6,991	6,584	6,384
Aflac U.S.
Deferred policy acquisition costs:
Balance, beginning of year	3,544	3,491
Capitalization	486	626
Amortization	(570)	(573)	(534)
Foreign currency translation and other	(10)	0
Balance, end of year	$ 3,450	$ 3,544	$ 3,491