Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			6 Months Ended					3 Months Ended		6 Months Ended		1 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2010 Accounting Standards Update 2010-26	Jun. 30, 2012 Aflac Japan	Jun. 30, 2011 Aflac Japan	Dec. 31, 2011 Aflac Japan	Dec. 31, 2010 Retained earnings: Accounting Standards Update 2010-26	Dec. 31, 2010 Accumulated Other Comprehensive Income (Loss) Accounting Standards Update 2010-26	Jun. 30, 2012 Dollar denominated investment portfolio Aflac Japan	Jun. 30, 2011 Dollar denominated investment portfolio Aflac Japan	Jun. 30, 2012 Dollar denominated investment portfolio Aflac Japan	Jun. 30, 2011 Dollar denominated investment portfolio Aflac Japan	Aug. 31, 2012 Lower Limit Settlement of IRS Examination Subsequent Event	Aug. 31, 2012 Upper Limit Settlement of IRS Examination Subsequent Event
Significant Accounting Policies [Line Items]
Aflac Japan's percentage of the Company's total revenues						77.00%	73.00%
Aflac Japan's percentage of the Company's total assets						87.00%		87.00%
Other comprehensive income foreign exchange gains or losses, deferred tax expense (benefit)											$ (96)	$ (112)	$ 61	$ (50)
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio											8.30%	36.40%	37.50%	35.80%
Adjustment to the shareholders' equity upon adoption of new DAC accounting guidance					(516)				(408)	(108)
Income tax expense (benefit)	$ 258	$ 170	$ 675	$ 373											$ (20)	$ (25)