Fair Value Measurements - Quantitative Information about Non Recurring Fair Value Measurement of Assets and Liabilities (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Residential Mortgage [Member] | Third Party Appraisal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation Technique(s)	Valuation of third party appraisal on underlying collateral		Valuation of third party appraisal on underlying collateral
Residential Mortgage [Member] | Loss Severity Rates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Significant Unobservable Inputs	Loss severity rates		Loss severity rates
Residential Mortgage [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	0.00%		0.00%
Residential Mortgage [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	100.00%		100.00%
Impaired loans [Member] | Third Party Appraisal On Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation Technique(s)	Valuation of third party appraisal on underlying collateral		Valuation of third party appraisal on underlying collateral
Impaired loans [Member] | Loss Severity Rates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Significant Unobservable Inputs	Loss severity rates		Loss severity rates
Impaired loans [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	0.00%		1.00%
Impaired loans [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Range of Inputs	81.00%		79.00%
Fair Value, Measurements, Nonrecurring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	$ 132		$ 222
Fair Value, Measurements, Nonrecurring [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	63	[1]	67	[1]
Fair Value, Measurements, Nonrecurring [Member] | Impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	$ 69	[2]	$ 155	[2]

[1] As of September 30, 2013 and December 31, 2012, the fair value of the loans held for sale was below cost. Certain residential mortgage loans held for sale have been classified as a Level 3 fair value measurement within the fair value hierarchy as the underlying real estate properties which determine fair value are illiquid assets as a result of market conditions and significant inputs in estimating fair value were unobservable. Additionally, the fair value of these properties is affected by, among other things, the location, the payment history and the completeness of the loan documentation.

[2] Certain commercial loans have undergone troubled debt restructurings and are considered impaired. As a matter of practical expedient, we measure the credit impairment of a collateral-dependent loan based on the fair value of the collateral asset. The collateral often involves real estate properties that are illiquid due to market conditions. As a result, these loans are classified as a Level 3 fair value measurement within the fair value hierarchy.