DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Advertising Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Advertising Costs [Line Items]
Advertising expense	$ 210	$ 224	$ 211
Aflac Japan
Advertising Costs [Line Items]
Advertising expense	100	100	82
Aflac U.S.
Advertising Costs [Line Items]
Advertising expense	$ 110	$ 124	$ 129