REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,652	$ 4,772
Net premium income	4,593	4,681
Direct benefits and claims	2,776	3,028
Benefits and claims, net	2,735	2,939
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	8	10
Assumed benefits and claims from other companies	(8)	(10)
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(19)	(24)
Assumed premiums earned	26	0
Ceded benefits and claims	(8)	(25)
Assumed benefits and claims from other companies	24	0
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,123	3,150
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(114)	(116)
Assumed premiums earned	48	49
Ceded benefits and claims	(99)	(105)
Assumed benefits and claims from other companies	$ 42	$ 41

Amount of earned premiums assumed from other entities.

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