POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (105)	$ (134)	$ (408)	$ (437)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense			$ 264
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), prior year claims adjustment expense			$ 3
Prior year claims and claims adjustment expense excluding effect of foreign currency			$ 261
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency			64.00%