Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Notes payable		$ 4,991		$ 5,268
Parent Company
Condensed Financial Statements, Captions [Line Items]
Notes payable		5,008		5,285
Parent Company | 3.45% senior notes paid August 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable		0		300
Parent Company | 2.65% senior notes due February 2017
Condensed Financial Statements, Captions [Line Items]
Notes payable	[1]	652		653
Parent Company | 8.50% senior notes due May 2019
Condensed Financial Statements, Captions [Line Items]
Notes payable		0	[2]	850
Parent Company | 2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Notes payable		550		0
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Notes payable		350		350
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	[3]	749		749
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Notes payable		448	[3]	0
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Notes payable	[3]	397		397
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Notes payable	[3]	448		448
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		83
Parent Company | 1.84% yen-denominated Samurai notes due July 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable		131		131
Parent Company | 3.60% yen-denominated loan paid July 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable		0		83
Parent Company | 3.00% yen-denominated loan paid August 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable		$ 0		$ 41

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

[2] Redeemed in April 2015

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