POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (167)	$ (192)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (91)
Percentage of total prior year claims and claims adjustment expense	54.00%