POLICY LIABILITIES - Additional Information (Details) - Health insurance - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (320)	$ (136)
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (101)
Percentage of total prior year claims and claims adjustment expense	32.00%
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	$ (100)
Percentage of total prior year claims and claims adjustment expense excluding effect of foreign currency	31.00%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years claims and claims adjustment expense	$ (219)
Percentage of total prior year claims and claims adjustment expense	68.00%
Prior Year Claims And Claims Adjustment Expense From Refinement of Estimates	$ (137)