Schedule II - Aflac Incorporated (Parent Only) - Summary of Notes Payable (Detail 1) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 5,339	$ 4,951
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
Parent Company | 2.40% senior notes due March 2020
Condensed Financial Statements, Captions [Line Items]
Notes payable	547	546
Parent Company | 4.00% senior notes due February 2022
Condensed Financial Statements, Captions [Line Items]
Notes payable	348	348
Parent Company | 3.625% senior notes due June 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	696	696
Parent Company | 3.625% senior notes due November 2024
Condensed Financial Statements, Captions [Line Items]
Notes payable	745	744
Parent Company | 3.25% senior notes due March 2025
Condensed Financial Statements, Captions [Line Items]
Notes payable	445	445
Parent Company | 2.875% senior notes due October 2026
Condensed Financial Statements, Captions [Line Items]
Notes payable	298	0
Parent Company | 6.90% senior notes due December 2039
Condensed Financial Statements, Captions [Line Items]
Notes payable	220	393
Parent Company | 6.45% senior notes due August 2040
Condensed Financial Statements, Captions [Line Items]
Notes payable	254	445
Parent Company | 4.00% senior notes due October 2046
Condensed Financial Statements, Captions [Line Items]
Notes payable	394	0
Parent Company | 5.50% subordinated notes due September 2052
Condensed Financial Statements, Captions [Line Items]
Notes payable	486	486
Parent Company | 2.26% yen-denominated Uridashi notes paid September 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	0	83
Parent Company | 1.84% yen-denominated Samurai notes paid July 2016
Condensed Financial Statements, Captions [Line Items]
Notes payable	0	131
Parent Company | Yen-denominated loan variable interest rate due September 2021
Condensed Financial Statements, Captions [Line Items]
Notes payable	43	0
Parent Company | Yen-denominated loan variable interest rate due September 2023
Condensed Financial Statements, Captions [Line Items]
Notes payable	$ 214	$ 0