Servicing Assets and Residual Interests Economic Assumptions (Detail)	Dec. 31, 2011 years	Dec. 31, 2010 years
Fixed Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	7.2	6.7
Prepayment Speed (annual)	8.80%	10.70%
Discount Rate (annual)	10.50%	10.30%
Adjustable Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	3.7	3.6
Prepayment Speed (annual)	22.80%	23.30%
Discount Rate (annual)	11.40%	11.30%