POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (166)	$ (136)	$ (302)	$ (303)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense			$ 188
Percentage of total prior year claims and claims adjustment expense			62.00%
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			$ 187
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency			62.00%