Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Derivative
Valuation adjustments related to the credit risk associated with counterparties of customer accommodation derivative contracts	$ 17	$ 18
Derivative Liability, Fair Value, Amount Offset Against Collateral	704	785
Maximum length of time hedged in cash flow hedge	2 years 11 months
Interest Rate Floor | Cash Flow Hedging
Derivative
Deferred gains, net of tax, on cash flow hedges were recorded in accumulated other comprehensive income	37	50
Net deferred gains, net of tax, recorded in accumulated other comprehensive income are expected to be reclassified into earnings during the next twelve months	3
Interest Rate Contract
Derivative
Notional amount of the risk participation agreements	1,176	1,006
Credit Risk Derivatives Average Life	3 years 7 months 6 days
Fair value of risk participation agreements	2	2
Interest Rate Contract | Lender Concentration Risk
Derivative
Notional amount of the risk participation agreements	1,200	1,000
Total collateral (up to and exceeding 100% of the net position)
Derivative
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 875	$ 927