Servicing Assets and Residual Interests Economic Assumptions (Detail)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fixed Rate Residential Mortgage
Servicing Assets at Amortized Value
Weighted- Average Life (in years)	7 years 3 months 18 days	7 years 6 months 0 days
Prepayment Speed (annual)	8.80%	8.20%
Discount Rate (annual)	10.00%	10.60%
Adjustable Rate Residential Mortgage
Servicing Assets at Amortized Value
Weighted- Average Life (in years)	3 years 6 months 0 days	3 years 9 months 18 days
Prepayment Speed (annual)	23.40%	21.90%
Discount Rate (annual)	11.40%	11.50%