REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,752	$ 4,915	$ 9,476	$ 9,605
Net premium income	4,665	4,823	9,303	9,425
Direct benefits and claims	3,117	3,332	6,246	6,435
Benefits and claims, net	3,039	3,254	6,091	6,279
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(13)	(12)	(25)	(24)
Assumed premiums earned	1	2	3	4
Ceded benefits and claims	(11)	(7)	(22)	(17)
Assumed benefits and claims from other companies	0	2	2	2
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,222	3,402	6,416	6,581
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(130)	(141)	(260)	(275)
Assumed premiums earned	55	59	109	115
Ceded benefits and claims	(119)	(129)	(241)	(250)
Assumed benefits and claims from other companies	52	56	106	109
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	13	15	26	29
Assumed benefits and claims from other companies	$ (13)	$ (15)	$ (26)	$ (29)

Amount of earned premiums assumed from other entities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Amount of earned premiums ceded to other entities.

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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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