Servicing of Residential Loans - Schedule of Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Minimum [Member]
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Weighted-average life in years	5 years 7 months 6 days	6 years 1 month 0 days
Weighted-average stated borrower interest rate on underlying collateral	4.31%	3.73%
Discount rates	9.30%	9.50%
Weighted-average conditional prepayment rates	6.08%	3.00%
Weighted-average conditional default rates	0.59%	0.50%
Maximum [Member]
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Weighted-average life in years	7 years 9 months 18 days	9 years 7 months 0 days
Weighted-average stated borrower interest rate on underlying collateral	4.67%	4.54%
Discount rates	9.50%	12.30%
Weighted-average conditional prepayment rates	8.76%	8.10%
Weighted-average conditional default rates	0.83%	2.00%