Acquisitions and Discontinued Operations - Quantitative Information about Level 3 Fair Value Measurements (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Fair Value, Option, Quantitative Disclosures [Line Items]
Portfolio loans held for sale accounted for at fair value	$ 0	$ 0	$ 0
Level 3 [Member] | Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Portfolio loans held for sale accounted for at fair value	$ 169,000,000
Portfolio loans accounted for at fair value		$ 191,000,000	$ 201,000,000
Valuation Techniques	Market approach for September 2015 and Discounted cash flow for September and December 2014
Minimum [Member] | Level 3 [Member] | Portfolio Loan Indicative Bids [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	84.50%
Minimum [Member] | Level 3 [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		5.40%	5.00%
Minimum [Member] | Level 3 [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		2.00%	2.00%
Minimum [Member] | Level 3 [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		3.90%	3.60%
Minimum [Member] | Level 3 [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		0.86%	0.93%
Maximum [Member] | Level 3 [Member] | Portfolio Loan Indicative Bids [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	104.00%
Maximum [Member] | Level 3 [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		5.60%	5.80%
Maximum [Member] | Level 3 [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		77.00%	77.00%
Maximum [Member] | Level 3 [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		4.00%	3.90%
Maximum [Member] | Level 3 [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		1.70%	1.91%
Weighted Average [Member] | Level 3 [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		5.50%	5.25%
Weighted Average [Member] | Level 3 [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		25.66%	25.71%
Weighted Average [Member] | Level 3 [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		3.92%	3.69%
Weighted Average [Member] | Level 3 [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		1.12%	1.24%