POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (136)	$ (167)
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	67.00%
Liability for unpaid claims and claims adjustment expense, foreign currency translation gain (loss), prior year claims adjustment expense	$ 1
Prior year claims and claims adjustment expense excluding effect of foreign currency	$ 90
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency	66.00%