POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (133)	$ (138)	$ (325)	$ (260)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense			$ (210)
Percentage of total prior year claims and claims adjustment expense			65.00%
Liability for unpaid claims and claims adjustment expense, foreign currency translation gain (loss)			$ (10)
Prior year claims and claims adjustment expense excluding effect of foreign currency			$ (200)
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency			62.00%