Servicing Assets and Residual Interests Economic Assumptions (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fixed Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	6 years 10 months 24 days	7 years 2 months 12 days
Prepayment Speed (annual)	9.60%	8.80%
Discount Rate (annual)	10.40%	10.50%
Adjustable Rate Residential Mortgage
Servicing Assets at Amortized Value [Line Items]
Weighted- Average Life (in years)	3 years 9 months 18 days	3 years 8 months 12 days
Prepayment Speed (annual)	22.00%	22.80%
Discount Rate (annual)	11.40%	11.40%