Components of Income Tax Expense (Benefit) Applicable to Pretax Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Provision of Income Taxes [Line Items]
Current									$ 891	$ 862	$ 830
Deferred									137	379	(92)
Total income tax expense	(288)	(361)	(173)	(205)	(230)	(365)	(308)	(338)	1,028	1,241	738
Aflac Japan
Reconciliation of Provision of Income Taxes [Line Items]
Current									358	513	565
Deferred									(290)	546	62
Total income tax expense									68	1,059	627
Aflac U.S.
Reconciliation of Provision of Income Taxes [Line Items]
Current									533	349	265
Deferred									427	(167)	(154)
Total income tax expense									$ 960	$ 182	$ 111