STATUTORY ACCOUNTING AND DIVIDEND RESTRICTIONS - Reconciliation of Capital and Surplus Between Sap and Practices Permitted by the State of Nebraska (Detail) - Aflac - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Statutory Accounting Practices [Line Items]
Capital and surplus, Nebraska state basis	$ 11,001	$ 11,221
Capital and surplus, NAIC basis	10,140	10,417
Lease Deposits
Statutory Accounting Practices [Line Items]
State permitted practice amount	(43)	(40)
Reinsurance
Statutory Accounting Practices [Line Items]
State permitted practice amount	$ (818)	$ (764)

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Amount of each item listed to reconcile the differences as of the balance sheet date resulting from applying state permitted statutory accounting practices rather than statutory accounting practices permitted by National Association of Insurance Commissioners.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24746-158529

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The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

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- Definition

Amount of statutory capital and surplus computed using statutory accounting practices prescribed by the National Association of Insurance Commissioners.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

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