REINSURANCE - Effect of Reinsurance on Premiums and Benefits and Claims (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Effects of Reinsurance [Line Items]
Direct premium income	$ 4,833	$ 4,724
Net premium income	4,745	4,638
Direct benefits and claims	3,119	3,129
Benefits and claims, net	3,042	3,052
All other
Effects of Reinsurance [Line Items]
Ceded premiums	(15)	(12)
Assumed premiums earned	2	2
Ceded benefits and claims	(12)	(11)
Assumed benefits and claims from other companies	0	2
Aflac Japan
Effects of Reinsurance [Line Items]
Net premium income	3,263	3,194
Aflac Japan \| Closed Block
Effects of Reinsurance [Line Items]
Ceded premiums	(129)	(130)
Assumed premiums earned	54	54
Ceded benefits and claims	(117)	(122)
Assumed benefits and claims from other companies	52	54
Intercompany eliminations
Effects of Reinsurance [Line Items]
Ceded benefits and claims	12	13
Assumed benefits and claims from other companies	$ (12)	$ (13)

Amount of earned premiums assumed from other entities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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