Profits Repatriated by Aflac Japan to Aflac U.S. (Detail) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2011 JPY (¥)	Dec. 31, 2010 USD ($)	Dec. 31, 2010 JPY (¥)	Dec. 31, 2009 USD ($)	Dec. 31, 2009 JPY (¥)
Intercompany Foreign Currency Balance [Line Items]
Profit repatriation	$ 143	¥ 11,000	$ 317	¥ 28,700	$ 230	¥ 20,000