DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Lease and Rental Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Lease and Rental Expense [Line Items]
Lease and rental expense	$ 73	$ 75	$ 75
Aflac Japan
Lease and Rental Expense [Line Items]
Lease and rental expense	53	52	53
Aflac U.S.
Lease and Rental Expense [Line Items]
Lease and rental expense	16	21	21
All other
Lease and Rental Expense [Line Items]
Lease and rental expense	$ 4	$ 2	$ 1