REINSURANCE Additional Information (Detail) $ in Millions, ¥ in Billions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2016 USD ($)
Effects of Reinsurance [Line Items]
Percent change in spot yen/dollar exchange rate	3.00%
Percent change in ceded reserves	2.00%
Aflac Japan
Effects of Reinsurance [Line Items]
Committed reinsurance facility | ¥		¥ 110
Aflac Japan | Closed Block- Tranche Three
Effects of Reinsurance [Line Items]
Coinsurance reinsurance ceded percentage	30.00%
Reinsurance assumed percentage	27.00%
Aflac Japan | Closed Medical Block - Tranche Two
Effects of Reinsurance [Line Items]
Coinsurance reinsurance ceded percentage	16.70%
Aflac Japan | Closed Medical Block - Tranche One
Effects of Reinsurance [Line Items]
Coinsurance reinsurance ceded percentage	33.30%
Aflac Japan | Closed block
Effects of Reinsurance [Line Items]
Reinsurance assumed percentage	8.35%
Reinsurance deferred profit liability	$ 954
Reinsurance recoverable	908		$ 860
Letter of credit | Closed Block- Tranche Three
Effects of Reinsurance [Line Items]
Collateral posted for reinsurance	$ 90