REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,734	$ 5,119	$ 14,210	$ 14,724
Net premium income	4,648	5,022	13,951	14,447
Direct benefits and claims	3,157	3,463	9,403	9,898
Benefits and claims, net	3,083	3,378	9,174	9,657
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(12)	(13)	(37)	(37)
Assumed premiums earned	2	2	5	6
Ceded benefits and claims	(9)	(10)	(31)	(26)
Assumed benefits and claims from other companies	0	1	2	2
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,200	3,596	9,616	10,177
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(130)	(148)	(390)	(423)
Assumed premiums earned	54	62	163	177
Ceded benefits and claims	(118)	(135)	(359)	(385)
Assumed benefits and claims from other companies	53	59	159	168
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	13	16	39	44
Assumed benefits and claims from other companies	$ (13)	$ (16)	$ (39)	$ (44)

Amount of earned premiums assumed from other entities.

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-Name Accounting Standards Codification
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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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Amount, before effect of policies assumed or ceded, of expense related to provision for policy benefits and costs incurred.

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Amount of reduction of provision for policy benefits and costs incurred for policies ceded.

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