Reconciliation of Net Assets on Gaap Basis to Capital and Surplus Determined on Nebraska Statutory Accounting Basis (Detail) (Aflac, USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Statutory Accounting Practices [Line Items]
Net assets on GAAP basis	$ 15,814	$ 12,902
Capital and surplus, Nebraska state basis	6,371	6,740
Adjustment of carrying values of investments
Statutory Accounting Practices [Line Items]
Amount of Reconciling Item	(1,707)	148
Deferred Acquisition Costs
Statutory Accounting Practices [Line Items]
Amount of Reconciling Item	(10,417)	(9,566)
Adjustment to policy liabilities
Statutory Accounting Practices [Line Items]
Amount of Reconciling Item	2,286	2,309
Adjustment to deferred income taxes
Statutory Accounting Practices [Line Items]
Amount of Reconciling Item	728	670
Other
Statutory Accounting Practices [Line Items]
Amount of Reconciling Item	$ (333)	$ 277