STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS - Additional Information (Detail) $ in Millions, ¥ in Billions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 JPY (¥)
Statutory Accounting Practices [Line Items]
Statutory accounting practices, statutory capital and surplus required	$ 1,400
Net Derivatives Notional Amount	25,751	$ 43,927
Aflac
Statutory Accounting Practices [Line Items]
Net Income, Nebraska state basis	2,600	2,800	$ 2,300
Capital and surplus, statutory accounting practices of the state or country basis	11,001	11,221
Amount available for dividend distribution without prior approval from regulatory agency	2,600
Dividends declared	2,600
Aflac Japan
Statutory Accounting Practices [Line Items]
Capital and surplus, statutory accounting practices of the state or country basis	6,700	$ 5,600
Twenty Seventeen profit repatriation
Statutory Accounting Practices [Line Items]
Intercompany transfer profit repatriation, reduction in amount received	$ 1
Foreign currency forwards and options | Twenty Seventeen profit repatriation
Statutory Accounting Practices [Line Items]
Net Derivatives Notional Amount | ¥				¥ 90.9
Foreign currency forwards and options | Future profit repatriation
Statutory Accounting Practices [Line Items]
Net Derivatives Notional Amount | ¥				¥ 49.5