REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,711	$ 4,823	$ 14,236	$ 14,365
Net premium income	4,623	4,736	13,969	14,109
Direct benefits and claims	3,051	3,106	9,054	9,185
Benefits and claims, net	2,985	3,027	8,822	8,958
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(22)	(17)	(69)	(50)
Assumed premiums earned	1	0	5	4
Ceded benefits and claims	(10)	(18)	(54)	(41)
Assumed benefits and claims from other companies	0	1	3	1
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,168	3,241	9,476	9,593
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(116)	(121)	(349)	(361)
Assumed premiums earned	49	51	146	151
Ceded benefits and claims	(103)	(111)	(314)	(331)
Assumed benefits and claims from other companies	47	49	133	144
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	10	11	29	31
Assumed benefits and claims from other companies	$ (10)	$ (11)	$ (29)	$ (31)

Amount of earned premiums assumed from other entities.

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