DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Advertising Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Advertising Costs [Line Items]
Advertising expense	$ 219	$ 218	$ 210
Aflac Japan
Advertising Costs [Line Items]
Advertising expense	101	108	100
Aflac U.S.
Advertising Costs [Line Items]
Advertising expense	$ 118	$ 110	$ 110