REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,426	$ 4,711	$ 13,567	$ 14,236
Net premium income	4,372	4,623	13,406	13,969
Direct benefits and claims	2,649	3,051	8,112	9,054
Benefits and claims, net	2,609	2,985	7,996	8,822
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	8	10	24	29
Assumed benefits and claims from other companies	(8)	(10)	(24)	(29)
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(19)	(22)	(54)	(69)
Assumed premiums earned	27	1	84	5
Ceded benefits and claims	(9)	(10)	(25)	(54)
Assumed benefits and claims from other companies	21	0	71	3
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	2,934	3,168	9,045	9,476
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(107)	(116)	(329)	(349)
Assumed premiums earned	45	49	138	146
Ceded benefits and claims	(94)	(103)	(288)	(314)
Assumed benefits and claims from other companies	$ 42	$ 47	$ 126	$ 133

Amount of earned premiums assumed from other entities.

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