Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended			9 Months Ended					3 Months Ended		9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2009 Accounting Standards Update 2010-26	Sep. 30, 2013 Aflac Japan	Sep. 30, 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	Sep. 30, 2013 Dollar denominated investment portfolio Aflac Japan	Sep. 30, 2012 Dollar denominated investment portfolio Aflac Japan	Sep. 30, 2013 Dollar denominated investment portfolio Aflac Japan	Sep. 30, 2012 Dollar denominated investment portfolio Aflac Japan
Significant Accounting Policies [Line Items]
Aflac Japan's percentage of the Company's total revenues							75.00%	78.00%
Percentage of the Company Assets							85.00%		87.00%
Valuation allowance increase (decrease) during period related to deferred tax assets associated with unrealized investment losses	$ (237)	$ 237
Income tax expense (benefit) related to items of other comprehensive income (loss)	(211)		347	(967)	569							(38)	(86)	614	(25)
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio												(102.30%)	34.40%	38.10%	35.20%
Effective income tax rate excluding income tax expense (benefit) related to Aflac Japan's dollar-denominated portfolio and release of valuation allowance												38.80%
Adjustment to shareholders' equity upon adoption of new DAC accounting guidance						$ (458)				$ (391)	$ (67)