INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	$ 0
Due after one year through five years	1,147
Due after five years through 10 years	285
Due after 10 years	2,037
Total perpetual securities available for sale	3,469
Due in one year or less	0
Due after one year through five years	968
Due after five years through 10 years	218
Due after 10 years	1,771
Total perpetual securities available for sale	2,957
Aflac U.S.
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	0
Due after one year through five years	5
Due after five years through 10 years	0
Due after 10 years	159
Total perpetual securities available for sale	164
Due in one year or less	0
Due after one year through five years	5
Due after five years through 10 years	0
Due after 10 years	171
Total perpetual securities available for sale	$ 176