DEFERRED POLICY ACQUISITION COSTS AND INSURANCE EXPENSES - Advertising Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Advertising Costs [Line Items]
Advertising expense	$ 184	$ 219	$ 218
Aflac Japan
Advertising Costs [Line Items]
Advertising expense	72	101	108
Aflac U.S.
Advertising Costs [Line Items]
Advertising expense	$ 112	$ 118	$ 110