Summary of Dollar Values of Yen-Denominated Net Assets Which are Subject to Foreign Currency Translation Fluctuations (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Yen Denominated
Segment Reporting Information [Line Items]
Net asset (liabilities)	$ 2,399	$ 2,241
Aflac Japan
Segment Reporting Information [Line Items]
Net asset (liabilities)	10,998	8,907
Aflac Japan | Dollar Denominated
Segment Reporting Information [Line Items]
Net asset (liabilities)	(7,341)	(5,625)
Aflac Japan | Yen Denominated
Segment Reporting Information [Line Items]
Net asset (liabilities)	3,657	3,282
Parent Company | Yen Denominated
Segment Reporting Information [Line Items]
Net asset (liabilities)	$ (1,258)	$ (1,041)