Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			3 Months Ended					3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2009 Accounting Standards Update 2010-26	Mar. 31, 2013 Aflac Japan	Mar. 31, 2012 Aflac Japan	Dec. 31, 2012 Aflac Japan	Dec. 31, 2009 Retained earnings: Accounting Standards Update 2010-26	Dec. 31, 2009 Accumulated Other Comprehensive Income (Loss) Accounting Standards Update 2010-26	Mar. 31, 2013 Dollar denominated investment portfolio Aflac Japan	Mar. 31, 2012 Dollar denominated investment portfolio Aflac Japan
Significant Accounting Policies [Line Items]
Income tax expense (benefit) related to items of other comprehensive income (loss)	$ (58)	$ 311							$ 424	$ 157
Aflac Japan's percentage of the Company's total revenues				75.00%	77.00%
Aflac Japan's percentage of the Company's total assets				86.00%		87.00%
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio									43.00%	44.50%
Adjustment to shareholders' equity upon adoption of new DAC accounting guidance			$ (458)				$ (391)	$ (67)