Acquisitions and Discontinued Operations - Significant Unobservable Inputs Used to Measure Fair Value (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Prepayment speed Trust loans and portfolio loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	10.02%
Expected credit losses [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	52.30%
Loan discount rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	4.79%
Expected defaults [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	13.44%
Discount rate trust securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	4.14%
Trust loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Valuation Techniques	Discounted cash flow
Trust loans and portfolio loans accounted for at fair value	$ 2,526
Trust securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Valuation Techniques	Discounted cash flow
Trust loans and portfolio loans accounted for at fair value	$ 2,159
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%
Minimum [Member] | Expected credit losses [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	2.00%
Minimum [Member] | Loan discount rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	2.40%
Minimum [Member] | Expected defaults [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	8.13%
Minimum [Member] | Discount rate trust securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	1.50%
Maximum [Member] | Prepayment speed Trust loans and portfolio loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	26.00%
Maximum [Member] | Expected credit losses [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	80.00%
Maximum [Member] | Loan discount rates [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	6.60%
Maximum [Member] | Expected defaults [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	21.50%
Maximum [Member] | Discount rate trust securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable input weighted-average	6.10%