INVESTMENTS - Economic Maturities of Investments in Perpetual Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	$ 322
Due after one year through five years	1,251
Due after five years through 10 years	468
Due after 10 years	2,623
Total perpetual securities available for sale	4,664
Due in one year or less	325
Due after one year through five years	1,304
Due after five years through 10 years	498
Due after 10 years	2,422
Total perpetual securities available for sale	4,549
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	165
Total perpetual securities available for sale	$ 170