Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 31, 2012 New Accounting Pronouncement, Effect Accounting Standards Update 2010-26 Lower Limit	Jan. 31, 2012 New Accounting Pronouncement, Effect Accounting Standards Update 2010-26 Upper Limit	Dec. 31, 2011 Aflac Japan	Dec. 31, 2010 Aflac Japan	Dec. 31, 2009 Aflac Japan	Dec. 31, 2011 Aflac Japan Dollar-denominated investment portfolio	Dec. 31, 2010 Aflac Japan Dollar-denominated investment portfolio	Dec. 31, 2009 Aflac Japan Dollar-denominated investment portfolio
Significant Accounting Policies [Line Items]
Aflac Japan's percentage of the Company's total revenues						75.00%	75.00%	73.00%
Aflac Japan's percentage of the Company's total assets						87.00%	86.00%
Other comprehensive income foreign exchange gains or losses, deferred tax expense (benefit)	$ (185)	$ (339)	$ 39						$ (152)	$ (322)	$ 12
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio									34.00%	31.00%	35.00%
Estimated adjustment to the opening balance of retained earnings upon adoption of new accounting guidance				$ 400	$ 500
Estimated adjustment to the opening balance of retained earnings upon adoption of new accounting guidance, percentage of equity				3.60%	4.50%