DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Lease and Rental Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease and Rental Expense [Line Items]
Lease and rental expense	$ 75	$ 75	$ 65
Aflac Japan
Lease and Rental Expense [Line Items]
Lease and rental expense	52	53	46
Aflac U.S.
Lease and Rental Expense [Line Items]
Lease and rental expense	21	21	18
All other
Lease and Rental Expense [Line Items]
Lease and rental expense	$ 2	$ 1	$ 1