Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable Parenthetical (Detail) $ in Millions, ¥ in Billions	Dec. 31, 2015 USD ($)	Dec. 31, 2015 JPY (¥)	Apr. 30, 2015	Mar. 31, 2015 USD ($)	Dec. 31, 2014 JPY (¥)	Nov. 30, 2014 USD ($)	Jun. 30, 2013 USD ($)	Oct. 31, 2012 USD ($)	Sep. 30, 2012 USD ($)	Jul. 31, 2012 USD ($)	Feb. 29, 2012 USD ($)	Jul. 31, 2011 JPY (¥)	Aug. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	May. 31, 2009 USD ($)	Sep. 30, 2006 JPY (¥)
3.45% senior notes paid August 2015
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate					3.45%
Debt instrument, principal amount													$ 300
2.65% senior notes due February 2017
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.65%	2.65%			2.65%					2.65%	2.65%
Debt instrument, principal amount	$ 400									$ 250	$ 400
8.50% senior notes due May 2019
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate			8.50%		8.50%
Debt instrument, principal amount															$ 850
2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.40%	2.40%		2.40%
Debt instrument, principal amount	$ 550			$ 550
4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%	4.00%			4.00%						4.00%
Debt instrument, principal amount	$ 350										$ 350
3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%	3.625%			3.625%		3.625%
Debt instrument, principal amount	$ 700						$ 700
3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%	3.625%			3.625%	3.625%
Debt instrument, principal amount	$ 750					$ 750
3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.25%	3.25%		3.25%
Debt instrument, principal amount	$ 450			$ 450
6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.90%	6.90%			6.90%
Debt instrument, principal amount														$ 400
6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.45%	6.45%			6.45%
Debt instrument, principal amount													$ 450
5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	5.50%	5.50%			5.50%			5.50%	5.50%
Debt instrument, principal amount	$ 500							$ 50	$ 450
2.26% yen-denominated Uridashi notes due September 2016
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.26%	2.26%			2.26%
Debt instrument, principal amount | ¥		¥ 8.0			¥ 8.0											¥ 10.0
1.84% yen-denominated Samurai notes due July 2016
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.84%	1.84%			1.84%							1.84%
Debt instrument, principal amount | ¥		¥ 15.8			¥ 15.8							¥ 15.8
3.60% yen-denominated loan paid July 2015
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate					3.60%
Debt instrument, principal amount | ¥					¥ 10.0
3.00% yen-denominated loan paid August 2015
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate					3.00%
Debt instrument, principal amount | ¥					¥ 5.0
Parent Company | 3.45% senior notes paid August 2015
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate					3.45%
Parent Company | 2.65% senior notes due February 2017
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.65%	2.65%			2.65%
Parent Company | 8.50% senior notes due May 2019
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate					8.50%
Parent Company | 2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.40%	2.40%
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%	4.00%			4.00%
Parent Company | 3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%	3.625%			3.625%
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.625%	3.625%			3.625%
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.25%	3.25%
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.90%	6.90%			6.90%
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.45%	6.45%			6.45%
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	5.50%	5.50%			5.50%
Parent Company | 2.26% yen-denominated Uridashi notes due September 2016
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.26%	2.26%			2.26%
Debt instrument, principal amount | ¥		¥ 10.0			¥ 10.0
Parent Company | 1.84% yen-denominated Samurai notes due July 2016
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	1.84%	1.84%			1.84%
Debt instrument, principal amount | ¥		¥ 15.8			¥ 15.8
Parent Company | 3.60% yen-denominated loan paid July 2015
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.60%	3.60%			3.60%
Debt instrument, principal amount | ¥		¥ 10.0			¥ 10.0
Parent Company | 3.00% yen-denominated loan paid August 2015
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	3.00%	3.00%			3.00%
Debt instrument, principal amount | ¥		¥ 5.0			¥ 5.0