Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Derivative [Line Items]
Collateral from counterparties to offset changes in the fair value of derivative assets	$ 1,200,000,000	$ 1,000,000,000	$ 1,200,000,000	$ 1,200,000,000
Valuation adjustments related to the credit risk associated with counterparties of customer accommodation derivative contracts	33,000,000	20,000,000		28,000,000
Collateral from counterparties to offset changes in the fair value of derivative liabilities	758,000,000	885,000,000	758,000,000	788,000,000
Reclassified gains (losses) from accumulated other comprehensive income into earnings as the original forecasted transaction was no longer probable of occurring within the originally specified time period			11,000,000
Cash Flow Hedging
Derivative [Line Items]
Maximum length of time hedged in cash flow hedge		41 months
Interest Rate Floor | Cash Flow Hedging
Derivative [Line Items]
Deferred gains, net of tax, on cash flow hedges were recorded in accumulated other comprehensive income	92,000,000	62,000,000	92,000,000	80,000,000
Net deferred gains, net of tax, recorded in accumulated other comprehensive income are expected to be reclassified into earnings		41,000,000
Interest Rate Contract | Lender Concentration Risk
Derivative [Line Items]
Notional amount of the risk participation agreements	722,000,000	971,000,000	722,000,000	808,000,000
Credit Risk Derivatives Average Life		2.8
Interest Rate Contract | Lender Concentration Risk | Servicing Contracts
Derivative [Line Items]
Fair value of risk participation agreements	$ 2,000,000	$ 2,000,000	$ 2,000,000	$ 2,000,000