Income Tax Effects of Temporary Differences that Gave Rise to Deferred Income Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred income tax liabilities:
Deferred policy acquisition costs	$ 3,104	$ 2,814
Unrealized gains on investment securities	397	114
Premiums receivable	153	151
Policy benefit reserves	1,896	1,583
Other	0	297
Total deferred income tax liabilities	5,550	4,959
Deferred income tax assets:
Depreciation	134	144
Policyholder protection corporation obligation	5	22
Difference in tax basis of investment in Aflac Japan	47	244
Other basis differences in investment securities	1,363	1,557
Unfunded retirement benefits	44	44
Other accrued expenses	64	70
Policy and contract claims	106	107
Unrealized exchange loss on yen-denominated notes payable	124	142
Deferred compensation	201	168
Capital loss carryforwards	784	374
Other	405	385
Total deferred income tax assets	3,277	3,257
Net deferred income tax liability	2,273	1,702
Current income tax liability	340	267
Total income tax liability	$ 2,613	$ 1,969