Servicing Assets and Residual Interests Economic Assumptions (Detail)	Mar. 31, 2012 years	Mar. 31, 2011 years
Fixed Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	7.5	8.1
Prepayment Speed (annual)	8.20%	7.20%
Discount Rate (annual)	10.60%	10.50%
Adjustable Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	3.8	3.4
Prepayment Speed (annual)	21.90%	24.00%
Discount Rate (annual)	11.50%	11.40%