POLICY LIABILITIES - Liability for Future Policy Benefits (Detail) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 97,783	$ 90,335
Intercompany eliminations
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts	[1]	$ (545)	$ (532)
Liability for future policy benefits, interest rate		2.00%
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		3.10%	3.20%	3.30%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		5.20%	5.30%	5.30%
Health insurance | Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 54,659	$ 50,941
Health insurance | Aflac Japan | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		0.60%
Health insurance | Aflac Japan | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		6.75%
Health insurance | Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 8,834	8,646
Health insurance | Aflac U.S. | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		3.00%
Health insurance | Aflac U.S. | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		8.00%
Life insurance | Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 33,993	30,520
Life insurance | Aflac Japan | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		0.60%
Life insurance | Aflac Japan | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		4.50%
Life insurance | Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 842	$ 760
Life insurance | Aflac U.S. | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		2.50%
Life insurance | Aflac U.S. | Upper Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		6.00%

[1] Elimination entry necessary due to recapture of a portion of policy liabilities ceded externally, as a result of the reinsurance retrocession transaction as described in Note 8 of the Notes to the Consolidated Financial Statements