Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,268		$ 4,891
Parent Company
Condensed Financial Statements, Captions [Line Items]
Notes payable	5,285		4,910
Parent Company | 3.45% senior notes due August 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable	300		300
Parent Company | 2.65% senior notes due February 2017
Condensed Financial Statements, Captions [Line Items]
Notes payable	653	[1]	655	[1]
Parent Company | 8.50% senior notes due May 2019
Condensed Financial Statements, Captions [Line Items]
Notes payable	850		850
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Notes payable	350	[2]	349	[2]
Parent Company | 3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	700		700
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Notes payable	749		0
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Notes payable	397	[2]	396	[2]
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Notes payable	448	[2]	448	[2]
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Notes payable	500		500
Parent Company | 2.26% yen-denominated Uridashi notes due September 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	83		95
Parent Company | 1.47% yen-denominated Samurai notes paid July 2014
Condensed Financial Statements, Captions [Line Items]
Notes payable	0		272
Parent Company | 1.84% yen-denominated Samurai notes due July 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	131		150
Parent Company | Variable interest rate yen-denominated Samurai notes paid July 2014
Condensed Financial Statements, Captions [Line Items]
Notes payable	0		52
Parent Company | 3.60% yen-denominated loan due July 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable	83		95
Parent Company | 3.00% yen-denominated loan due August 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 41		$ 48

[1] Principal amount plus an issuance premium that is being amortized over the life of the notes

[2] Principal amount net of an issuance discount that is being amortized over the life of the notes