POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (215)	$ (105)	$ (739)	$ (408)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense			$ (369)
Percentage of total prior year claims and claims adjustment expense			49.90%
Liability for unpaid claims and claims adjustment expense, foreign currency translation gain (loss), prior year claims adjustment expense			$ (11)
Prior year claims and claims adjustment expense excluding effect of foreign currency			$ (380)
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency			51.00%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense			$ (370)
Percentage of total prior year claims and claims adjustment expense			50.10%
Prior Year Claims And Claims Adjustment Expense From Refinement of Estimates			$ (143)