Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	3 Months Ended			12 Months Ended		3 Months Ended
	Dec. 31, 2010 Accounting Standards Update 2010-26	Mar. 31, 2012 Aflac Japan	Mar. 31, 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	Mar. 31, 2012 Dollar denominated investment portfolio [Member] Aflac Japan	Mar. 31, 2011 Dollar denominated investment portfolio [Member] Aflac Japan
Significant Accounting Policies [Line Items]
Aflac Japan's percentage of the Company's total revenues		77.00%	74.00%
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)							$ 157	$ 51
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio							44.50%	32.40%
Adjustment to the shareholders' equity upon adoption of new DAC accounting guidance	$ (516)				$ (408)	$ (108)