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
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	6.62%	6.16%	6.47%
Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	53.89%	52.29%	54.21%
Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	3.51%	3.89%	3.50%
Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	18.65%	13.84%	18.43%
Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	2.55%	3.29%	2.55%
Trust Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Trust loans and portfolio loans accounted for at fair value	$ 2,036	$ 2,487	$ 2,107
Valuation Techniques	Discounted cash flow	Discounted cash flow	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	$ 2,126	$ 1,834
Valuation Techniques	Discounted cash flow	Discounted cash flow	Discounted cash flow
Minimum [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	4.00%	4.00%	4.00%
Minimum [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	2.00%	2.00%	2.00%
Minimum [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	2.40%	1.80%	2.40%
Minimum [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	8.05%	8.13%	8.01%
Minimum [Member] | Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	1.60%	1.10%	1.60%
Maximum [Member] | Prepayment Speed Trust Loans and Portfolio Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	13.50%	13.50%	13.50%
Maximum [Member] | Loss Severity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	79.50%	80.00%	79.50%
Maximum [Member] | Loan Discount Rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	10.50%	5.50%	10.50%
Maximum [Member] | Loan Default Rate [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	23.87%	22.00%	23.71%
Maximum [Member] | Discount Rate Trust Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	3.50%	5.00%	3.50%