Servicing Assets and Residual Interests Economic Assumptions (Detail)	Sep. 30, 2012 years	Sep. 30, 2011 years
Fixed Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	6.3	6.3
Prepayment Speed (annual)	11.00%	11.10%
Discount Rate (annual)	10.30%	10.50%
Adjustable Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	3.8	3.7
Prepayment Speed (annual)	21.70%	22.30%
Discount Rate (annual)	11.40%	11.40%