POLICY LIABILITIES - Liability for Future Policy Benefits (Detail) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 90,335	$ 86,368
Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		3.20%	3.30%	3.40%
Aflac U.S.
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		5.30%	5.30%	5.40%
Intercompany eliminations
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts	[1]	$ (532)	$ (583)
Liability for future policy benefits, interest rate		2.00%
Health insurance | Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 50,941	49,496
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		$ 8,646	8,442
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		7.00%
Life insurance | Aflac Japan
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability amounts		$ 30,520	28,318
Life insurance | Aflac Japan | Lower Limit
Liability for Future Policy Benefit, by Product Segment [Line Items]
Liability for future policy benefits, interest rate		1.00%
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		$ 760	$ 695
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