Economic Maturities of Investments in Perpetual Securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Aflac Japan
Investments Classified by Economic Maturity Date [Line Items]
Due in one year or less	$ 323
Due after one year through five years	1,876
Due after five years through 10 years	547
Due after 10 years	3,974
Total perpetual securities available for sale	6,720
Due in one year or less	389
Due after one year through five years	1,953
Due after five years through 10 years	565
Due after 10 years	3,364
Total perpetual securities available for sale	6,271
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	172
Total perpetual securities available for sale	177
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	163
Total perpetual securities available for sale	$ 168