Acquisitions and Discontinued Operations - Quantitative Information about Level 3 Fair Value Measurements (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Trust loans and portfolio loans accounted for at fair value	$ 191
Valuation Techniques	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		2,107
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		$ 1,834
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%	4.00%
Minimum [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	2.00%	2.00%
Minimum [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	3.90%	2.40%
Minimum [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	0.86%	8.01%
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	5.60%	13.50%
Maximum [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	77.00%	79.50%
Maximum [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	4.00%	10.50%
Maximum [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	1.70%	23.71%
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	5.50%	6.47%
Weighted Average [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	25.66%	54.21%
Weighted Average [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	3.92%	3.50%
Weighted Average [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	1.12%	18.43%
Weighted Average [Member] | Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		2.55%