REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,490	$ 4,752	$ 9,141	$ 9,525
Net premium income	4,441	4,664	9,034	9,346
Direct benefits and claims	2,687	2,975	5,463	6,003
Benefits and claims, net	2,653	2,897	5,387	5,837
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	8	10	16	19
Assumed benefits and claims from other companies	(8)	(10)	(16)	(19)
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(15)	(24)	(34)	(48)
Assumed premiums earned	30	3	57	4
Ceded benefits and claims	(9)	(21)	(17)	(45)
Assumed benefits and claims from other companies	27	1	50	2
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	2,987	3,158	6,111	6,308
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(109)	(116)	(223)	(232)
Assumed premiums earned	45	49	93	97
Ceded benefits and claims	(94)	(105)	(193)	(210)
Assumed benefits and claims from other companies	$ 42	$ 47	$ 84	$ 87

Amount of earned premiums assumed from other entities.

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