REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,752	$ 4,766	$ 9,525	$ 9,542
Net premium income	4,664	4,681	9,346	9,373
Direct benefits and claims	2,975	3,038	6,003	6,078
Benefits and claims, net	2,897	2,964	5,837	5,932
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(24)	(17)	(48)	(32)
Assumed premiums earned	3	1	4	3
Ceded benefits and claims	(21)	(12)	(45)	(24)
Assumed benefits and claims from other companies	1	0	2	0
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,158	3,172	6,308	6,352
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(116)	(119)	(232)	(240)
Assumed premiums earned	49	50	97	100
Ceded benefits and claims	(105)	(109)	(210)	(219)
Assumed benefits and claims from other companies	47	47	87	97
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	10	10	19	20
Assumed benefits and claims from other companies	$ (10)	$ (10)	$ (19)	$ (20)

Amount of earned premiums assumed from other entities.

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