Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable Parenthetical (Detail)	Dec. 31, 2014 3.45% senior notes due August 2015	Dec. 31, 2013 3.45% senior notes due August 2015	Aug. 31, 2010 3.45% senior notes due August 2015 USD ($)	Dec. 31, 2014 2.65% senior notes due February 2017 USD ($)	Dec. 31, 2013 2.65% senior notes due February 2017	Jul. 31, 2012 2.65% senior notes due February 2017 USD ($)	Feb. 29, 2012 2.65% senior notes due February 2017 USD ($)	Dec. 31, 2014 8.50% senior notes due May 2019	Dec. 31, 2013 8.50% senior notes due May 2019	May 31, 2009 8.50% senior notes due May 2019 USD ($)	Dec. 31, 2014 4.00% senior notes due February 2022 USD ($)	Dec. 31, 2013 4.00% senior notes due February 2022	Feb. 29, 2012 4.00% senior notes due February 2022 USD ($)	Dec. 31, 2014 3.625% senior notes due June 2023 USD ($)	Dec. 31, 2013 3.625% senior notes due June 2023	Jun. 30, 2013 3.625% senior notes due June 2023 USD ($)	Dec. 31, 2014 3.625% senior notes due November 2024 USD ($)	Nov. 30, 2014 3.625% senior notes due November 2024 USD ($)	Dec. 31, 2014 6.90% senior notes due December 2039	Dec. 31, 2013 6.90% senior notes due December 2039	Dec. 31, 2009 6.90% senior notes due December 2039 USD ($)	Dec. 31, 2014 6.45% senior notes due August 2040	Dec. 31, 2013 6.45% senior notes due August 2040	Aug. 31, 2010 6.45% senior notes due August 2040 USD ($)	Dec. 31, 2014 5.50% subordinated notes due September 2052 USD ($)	Dec. 31, 2013 5.50% subordinated notes due September 2052	Oct. 31, 2012 5.50% subordinated notes due September 2052 USD ($)	Sep. 30, 2012 5.50% subordinated notes due September 2052 USD ($)	Dec. 31, 2014 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Dec. 31, 2013 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Sep. 30, 2006 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Dec. 31, 2013 1.47% yen-denominated Samurai notes paid July 2014 JPY (¥)	Jul. 31, 2011 1.47% yen-denominated Samurai notes paid July 2014 JPY (¥)	Dec. 31, 2014 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Dec. 31, 2013 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Jul. 31, 2011 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Dec. 31, 2014 Variable interest rate yen-denominated Samurai notes paid July 2014 JPY (¥)	Dec. 31, 2013 Variable interest rate yen-denominated Samurai notes paid July 2014 JPY (¥)	Jul. 31, 2011 Variable interest rate yen-denominated Samurai notes paid July 2014 JPY (¥)	Dec. 31, 2014 3.60% yen-denominated loan due July 2015 JPY (¥)	Dec. 31, 2013 3.60% yen-denominated loan due July 2015 JPY (¥)	Dec. 31, 2014 3.00% yen-denominated loan due August 2015 JPY (¥)	Dec. 31, 2013 3.00% yen-denominated loan due August 2015 JPY (¥)	Dec. 31, 2014 Parent Company 3.45% senior notes due August 2015	Dec. 31, 2013 Parent Company 3.45% senior notes due August 2015	Dec. 31, 2014 Parent Company 2.65% senior notes due February 2017	Dec. 31, 2013 Parent Company 2.65% senior notes due February 2017	Dec. 31, 2014 Parent Company 8.50% senior notes due May 2019	Dec. 31, 2013 Parent Company 8.50% senior notes due May 2019	Dec. 31, 2014 Parent Company 4.00% senior notes due February 2022	Dec. 31, 2013 Parent Company 4.00% senior notes due February 2022	Dec. 31, 2014 Parent Company 3.625% senior notes due June 2023	Dec. 31, 2013 Parent Company 3.625% senior notes due June 2023	Dec. 31, 2014 Parent Company 3.625% senior notes due November 2024	Dec. 31, 2014 Parent Company 6.90% senior notes due December 2039	Dec. 31, 2013 Parent Company 6.90% senior notes due December 2039	Dec. 31, 2014 Parent Company 6.45% senior notes due August 2040	Dec. 31, 2013 Parent Company 6.45% senior notes due August 2040	Dec. 31, 2014 Parent Company 5.50% subordinated notes due September 2052	Dec. 31, 2013 Parent Company 5.50% subordinated notes due September 2052	Dec. 31, 2014 Parent Company 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Dec. 31, 2013 Parent Company 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Dec. 31, 2013 Parent Company 1.47% yen-denominated Samurai notes paid July 2014 JPY (¥)	Dec. 31, 2014 Parent Company 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Dec. 31, 2013 Parent Company 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Dec. 31, 2013 Parent Company Variable interest rate yen-denominated Samurai notes paid July 2014 JPY (¥)	Dec. 31, 2014 Parent Company 3.60% yen-denominated loan due July 2015 JPY (¥)	Dec. 31, 2013 Parent Company 3.60% yen-denominated loan due July 2015 JPY (¥)	Dec. 31, 2014 Parent Company 3.00% yen-denominated loan due August 2015 JPY (¥)	Dec. 31, 2013 Parent Company 3.00% yen-denominated loan due August 2015 JPY (¥)
Condensed Financial Statements, Captions [Line Items]
Notes payable, interest rate	3.45%	3.45%		2.65%	2.65%	2.65%	2.65%	8.50%	8.50%		4.00%	4.00%	4.00%	3.625%	3.625%	3.625%	3.625%	3.625%	6.90%	6.90%		6.45%	6.45%		5.50%	5.50%	5.50%	5.50%	2.26%	2.26%		1.47%		1.84%	1.84%	1.84%		1.30%		3.60%	3.60%	3.00%	3.00%	3.45%	3.45%	2.65%	2.65%	8.50%	8.50%	4.00%	4.00%	3.625%	3.625%	3.625%	6.90%	6.90%	6.45%	6.45%	5.50%	5.50%	2.26%	2.26%	1.47%	1.84%	1.84%	1.30%	3.60%	3.60%	3.00%	3.00%
Notes payable, principal amount			$ 300,000,000	$ 400,000,000		$ 250,000,000	$ 400,000,000			$ 850,000,000	$ 350,000,000		$ 350,000,000	$ 700,000,000		$ 700,000,000	$ 750,000,000	$ 750,000,000			$ 400,000,000			$ 450,000,000	$ 500,000,000		$ 50,000,000	$ 450,000,000	¥ 8,000,000,000	¥ 8,000,000,000	¥ 10,000,000,000	¥ 28,700,000,000	¥ 28,700,000,000.0	¥ 15,800,000,000	¥ 15,800,000,000	¥ 15,800,000,000.0	¥ 5,500,000,000	¥ 5,500,000,000	¥ 5,500,000,000.0	¥ 10,000,000,000	¥ 10,000,000,000	¥ 5,000,000,000	¥ 5,000,000,000																		¥ 10,000,000,000	¥ 10,000,000,000	¥ 28,700,000,000	¥ 15,800,000,000	¥ 15,800,000,000	¥ 5,500,000,000	¥ 10,000,000,000	¥ 10,000,000,000	¥ 5,000,000,000	¥ 5,000,000,000