Acquisitions and Discontinued Operations - Quantitative Information about Level 3 Fair Value Measurements (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Trust loans and portfolio loans accounted for at fair value	$ 187	$ 191
Valuation Techniques	Discounted cash flow	Discounted cash flow
Trust and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Trust loans and portfolio loans accounted for at fair value			2,036
Valuation Techniques			Discounted cash flow
Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Trust loans and portfolio loans accounted for at fair value			$ 1,796
Valuation Techniques			Discounted cash flow
Minimum [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	5.40%	5.40%	4.00%
Minimum [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	2.00%	2.00%	2.00%
Minimum [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	3.70%	3.90%	2.40%
Minimum [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	1.40%	0.86%	8.05%
Minimum [Member] | Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs			1.60%
Maximum [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	10.20%	5.60%	13.50%
Maximum [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	77.00%	77.00%	79.50%
Maximum [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	3.80%	4.00%	10.50%
Maximum [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	1.70%	1.70%	23.87%
Maximum [Member] | Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs			3.50%
Weighted Average [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	7.04%	5.50%	6.62%
Weighted Average [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	27.66%	25.66%	53.89%
Weighted Average [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	3.71%	3.92%	3.51%
Weighted Average [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	1.60%	1.12%	18.65%
Weighted Average [Member] | Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs			2.55%