Advertising Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Advertising Costs [Line Items]
Advertising expense	$ 258	$ 228	$ 213
Aflac Japan
Advertising Costs [Line Items]
Advertising expense	128	112	106
Aflac U.S.
Advertising Costs [Line Items]
Advertising expense	$ 130	$ 116	$ 107