Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail 2) $ in Millions, ¥ in Billions	Dec. 31, 2016 USD ($)	Dec. 31, 2016 JPY (¥)	Sep. 30, 2016 USD ($)	Sep. 30, 2016 JPY (¥)	Jul. 31, 2016	Dec. 31, 2015 USD ($)	Dec. 31, 2015 JPY (¥)	Mar. 31, 2015 USD ($)	Nov. 30, 2014 USD ($)	Jun. 30, 2013 USD ($)	Oct. 31, 2012 USD ($)	Sep. 30, 2012 USD ($)	Jul. 31, 2012 USD ($)	Feb. 29, 2012 USD ($)	Aug. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,339					$ 4,951
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%	2.65%
Debt instrument, principal amount	$ 400												$ 250	$ 400
2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.40%	2.40%				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%							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%			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%		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%	3.25%	3.25%
Debt instrument, principal amount	$ 450							$ 450
2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	2.875%	2.875%	2.875%	2.875%
Debt instrument, principal amount			$ 300
6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	6.90%	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%	6.45%
Debt instrument, principal amount															$ 450
4.00% senior notes due October 2046
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	4.00%	4.00%	4.00%	4.00%
Debt instrument, principal amount			$ 400
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%	5.50%
Debt instrument, principal amount	$ 500										$ 50	$ 450
2.26% yen-denominated Uridashi notes paid September 2016
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate			2.26%	2.26%		2.26%	2.26%
Debt instrument, principal amount | ¥							¥ 8.0
1.84% yen-denominated Samurai notes paid July 2016
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate					1.84%	1.84%	1.84%
Debt instrument, principal amount | ¥							¥ 15.8
Yen-denominated loan variable interest rate due September 2021
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.31%	0.31%
Debt instrument, principal amount | ¥		¥ 5.0		¥ 5.0
Yen-denominated loan variable interest rate due September 2023
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.46%	0.46%
Debt instrument, principal amount | ¥		¥ 25.0		¥ 25.0
Parent Company
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,339					$ 4,968
Parent Company | 2.65% senior notes due February 2017
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 649					$ 651
Debt instrument, interest rate	2.65%	2.65%				2.65%	2.65%
Parent Company | 2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 547					$ 546
Debt instrument, interest rate	2.40%	2.40%				2.40%	2.40%
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 348					$ 348
Debt instrument, interest rate	4.00%	4.00%				4.00%	4.00%
Parent Company | 3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 696					$ 696
Debt instrument, interest rate	3.625%	3.625%				3.625%	3.625%
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 745					$ 744
Debt instrument, interest rate	3.625%	3.625%				3.625%	3.625%
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 445					$ 445
Debt instrument, interest rate	3.25%	3.25%				3.25%	3.25%
Parent Company | 2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 298					$ 0
Debt instrument, interest rate	2.875%	2.875%
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 220					$ 393
Debt instrument, interest rate	6.90%	6.90%				6.90%	6.90%
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 254					$ 445
Debt instrument, interest rate	6.45%	6.45%				6.45%	6.45%
Parent Company | 4.00% senior notes due October 2046
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 394					$ 0
Debt instrument, interest rate	4.00%	4.00%
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 486					$ 486
Debt instrument, interest rate	5.50%	5.50%				5.50%	5.50%
Parent Company | 2.26% yen-denominated Uridashi notes paid September 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 0					$ 83
Debt instrument, interest rate						2.26%	2.26%
Debt instrument, principal amount | ¥							¥ 10.0
Parent Company | 1.84% yen-denominated Samurai notes paid July 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	0					$ 131
Debt instrument, interest rate						1.84%	1.84%
Debt instrument, principal amount | ¥							¥ 15.8
Parent Company | Yen-denominated loan variable interest rate due September 2021
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 43					$ 0
Debt instrument, interest rate	0.31%	0.31%
Debt instrument, principal amount | ¥		¥ 5.0
Parent Company | Yen-denominated loan variable interest rate due September 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 214					$ 0
Parent Company | Yen Denominated Loan Three Point Zero Zero Percent Due August Twenty Fifteen [Member]
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate	0.46%	0.46%
Debt instrument, principal amount | ¥		¥ 25.0