REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,766	$ 4,793	$ 9,542	$ 9,626
Net premium income	4,681	4,706	9,373	9,450
Direct benefits and claims	3,038	3,106	6,078	6,225
Benefits and claims, net	2,964	3,031	5,932	6,073
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(17)	(16)	(32)	(30)
Assumed premiums earned	1	2	3	3
Ceded benefits and claims	(12)	(12)	(24)	(23)
Assumed benefits and claims from other companies	0	2	0	1
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,172	3,227	6,352	6,490
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(119)	(126)	(240)	(256)
Assumed premiums earned	50	53	100	107
Ceded benefits and claims	(109)	(114)	(219)	(231)
Assumed benefits and claims from other companies	47	49	97	101
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	10	11	20	23
Assumed benefits and claims from other companies	$ (10)	$ (11)	$ (20)	$ (23)

Amount of earned premiums assumed from other entities.

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