POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (131)	$ (126)	$ (456)	$ (386)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense			$ (325)
Percentage of total prior year claims and claims adjustment expense			71.00%
Liability for unpaid claims and claims adjustment expense, foreign currency translation gain (loss)			$ (13)
Prior year claims and claims adjustment expense excluding effect of foreign currency			$ (312)
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency			68.00%