DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Advertising Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Advertising Costs [Line Items]
Advertising expense	$ 218	$ 210	$ 224
Aflac Japan
Advertising Costs [Line Items]
Advertising expense	108	100	100
Aflac U.S.
Advertising Costs [Line Items]
Advertising expense	$ 110	$ 110	$ 124