Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Derivative [Line Items]
Collateral from counterparties to offset changes in the fair value of derivative assets	$ 1,100	$ 837	$ 1,200
Valuation adjustments related to the credit risk associated with counterparties of customer accommodation derivative contracts	24	39	28
Collateral from counterparties to offset changes in the fair value of derivative liabilities	720	603	788
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	73	58	80
Net deferred gains, net of tax, recorded in accumulated other comprehensive income are expected to be reclassified into earnings	73
Interest Rate Contract | Lender Concentration Risk
Derivative [Line Items]
Notional amount of the risk participation agreements	824	834	808
Credit Risk Derivatives Average Life	2.4
Interest Rate Contract | Lender Concentration Risk | Servicing Contracts
Derivative [Line Items]
Fair value of risk participation agreements	$ 2	$ 1	$ 2