Fair Value - Significant Unobservable Inputs Used for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Weighted Average [Member] | Excess Servicing Spread [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	7 years 3 months 22 days
Fair Value Inputs, Discount rate	13.60%
Fair Value Inputs, Conditional prepayment rate	7.79%
Conditional default rate	1.51%
Weighted Average [Member] | Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	6.00%	8.00%
Fair Value Inputs, Conditional prepayment rate	2.72%	2.66%
Conditional default rate	2.55%	3.16%
Fair Value Inputs, Loss severity	82.87%	85.25%
Weighted Average [Member] | HMBS Related Obligations [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	3 years 11 months	4 years 1 month 0 days
Fair Value Inputs, Conditional repayment rate	21.21%	20.31%
Fair Value Inputs, Discount rate	2.36%	2.36%
Weighted Average [Member] | Interest Rate Lock Commitments [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Loan funding probability	80.90%	82.67%
Fair Value Inputs, Fair value of initial servicing rights multiple	4.06	4.52
Weighted Average [Member] | Loans Receivable [Member] | Reverse Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	4 years 8 months	4 years 5 months 0 days
Fair Value Inputs, Conditional repayment rate	21.68%	20.70%
Fair Value Inputs, Discount rate	2.76%	2.98%
Weighted Average [Member] | Loans Receivable [Member] | Mortgage Loans related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	8.00%	10.00%
Fair Value Inputs, Conditional prepayment rate	3.17%	2.99%
Conditional default rate	2.34%	2.90%
Fair Value Inputs, Loss severity	85.88%	88.09%
Weighted Average [Member] | Loans Receivable [Member] | Charged Off Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	30.19%	0.00%
Fair Value Inputs, Collection rate	2.46%	0.00%
Weighted Average [Member] | Receivables Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	0.50%	0.50%
Fair Value Inputs, Conditional prepayment rate	2.72%	2.66%
Conditional default rate	2.55%	3.16%
Fair Value Inputs, Loss severity	82.87%	85.25%
Weighted Average [Member] | Servicing Rights Carried at Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	6 years 7 months	6 years 10 months 0 days
Fair Value Inputs, Discount rate	9.55%	9.76%
Fair Value Inputs, Conditional prepayment rate	7.87%	7.06%
Conditional default rate	2.36%	2.90%
Weighted Average [Member] | Interest Rate Lock Commitments [Member] | Interest Rate Lock Commitments [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Loan funding probability	77.45%	78.23%
Fair Value Inputs, Fair value of initial servicing rights	3.83	4.21
Minimum [Member] | Excess Servicing Spread [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	7 years 2 months 27 days
Fair Value Inputs, Discount rate	13.60%
Fair Value Inputs, Conditional prepayment rate	7.71%
Conditional default rate	0.86%
Minimum [Member] | Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	6.00%	8.00%
Fair Value Inputs, Conditional prepayment rate	1.89%	1.93%
Conditional default rate	1.92%	1.98%
Fair Value Inputs, Loss severity	73.26%	72.94%
Minimum [Member] | HMBS Related Obligations [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	1 year 3 months	1 year 10 months 24 days
Fair Value Inputs, Conditional repayment rate	11.30%	10.22%
Fair Value Inputs, Discount rate	1.44%	1.38%
Minimum [Member] | Interest Rate Lock Commitments [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Loan funding probability	28.00%	46.50%
Fair Value Inputs, Fair value of initial servicing rights multiple	0.67	1.89
Minimum [Member] | Loans Receivable [Member] | Reverse Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	1 year 9 months	2 years
Fair Value Inputs, Conditional repayment rate	13.40%	10.67%
Fair Value Inputs, Discount rate	2.00%	1.79%
Minimum [Member] | Loans Receivable [Member] | Mortgage Loans related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	8.00%	10.00%
Fair Value Inputs, Conditional prepayment rate	2.24%	2.20%
Conditional default rate	1.68%	1.81%
Fair Value Inputs, Loss severity	76.12%	75.90%
Minimum [Member] | Loans Receivable [Member] | Charged Off Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	30.00%
Fair Value Inputs, Collection rate	2.34%
Minimum [Member] | Receivables Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	0.50%	0.50%
Fair Value Inputs, Conditional prepayment rate	1.89%	1.93%
Conditional default rate	1.92%	1.98%
Fair Value Inputs, Loss severity	73.26%	72.94%
Minimum [Member] | Servicing Rights Carried at Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	5 years 7 months	6 years
Fair Value Inputs, Discount rate	8.24%	8.87%
Fair Value Inputs, Conditional prepayment rate	5.04%	3.85%
Conditional default rate	0.28%	0.50%
Minimum [Member] | Interest Rate Lock Commitments [Member] | Interest Rate Lock Commitments [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Loan funding probability	3.44%	11.99%
Fair Value Inputs, Fair value of initial servicing rights	0.20	1.64
Maximum [Member] | Excess Servicing Spread [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	7 years 4 months 10 days
Fair Value Inputs, Discount rate	13.60%
Fair Value Inputs, Conditional prepayment rate	7.89%
Conditional default rate	2.31%
Maximum [Member] | Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	6.00%	8.00%
Fair Value Inputs, Conditional prepayment rate	3.33%	3.11%
Conditional default rate	3.81%	3.85%
Fair Value Inputs, Loss severity	89.78%	94.16%
Maximum [Member] | HMBS Related Obligations [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	7 years 8 months	7 years 9 months 18 days
Fair Value Inputs, Conditional repayment rate	48.65%	38.67%
Fair Value Inputs, Discount rate	3.06%	4.01%
Maximum [Member] | Interest Rate Lock Commitments [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Loan funding probability	100.00%	100.00%
Fair Value Inputs, Fair value of initial servicing rights multiple	5.47	5.30
Maximum [Member] | Loans Receivable [Member] | Reverse Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	12 years 4 months	12 years 10 months 24 days
Fair Value Inputs, Conditional repayment rate	42.20%	36.61%
Fair Value Inputs, Discount rate	3.65%	5.30%
Maximum [Member] | Loans Receivable [Member] | Mortgage Loans related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	8.00%	10.00%
Fair Value Inputs, Conditional prepayment rate	3.76%	3.78%
Conditional default rate	3.51%	3.60%
Fair Value Inputs, Loss severity	92.53%	96.67%
Maximum [Member] | Loans Receivable [Member] | Charged Off Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	32.25%
Fair Value Inputs, Collection rate	4.53%
Maximum [Member] | Receivables Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount rate	0.50%	0.50%
Fair Value Inputs, Conditional prepayment rate	3.33%	3.11%
Conditional default rate	3.81%	3.85%
Fair Value Inputs, Loss severity	89.78%	94.16%
Maximum [Member] | Servicing Rights Carried at Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years	9 years 3 months	10 years 9 months 18 days
Fair Value Inputs, Discount rate	29.16%	18.11%
Fair Value Inputs, Conditional prepayment rate	11.15%	8.08%
Conditional default rate	3.53%	3.74%
Maximum [Member] | Interest Rate Lock Commitments [Member] | Interest Rate Lock Commitments [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Loan funding probability	100.00%	100.00%
Fair Value Inputs, Fair value of initial servicing rights	5.47	5.60