Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Assets, Fair Value, Gross Amount Not Offset in the Consolidated Balance Sheets	$ 830	$ 514
Valuation adjustments related to the credit risk associated with counterparties of customer accommodation derivative contracts	16	12
Maximum Length Of Time Hedged In Interest Rate Cash Flow Hedge	5 years
Notional amount of the risk participations agreements	1,113	1,203
Credit Risk Derivatives Average Life	2 years 7 months 6 days
Fair value of risk participation agreements	2	3
Interest Rate Contract | Cash Flow Hedging
Derivative [Line Items]
Deferred gains, net of tax, on cash flow hedges were recorded in accumulated other comprehensive income	23	13
Net deferred gains, net of tax, recorded in accumulated other comprehensive income are expected to be reclassified into earnings	33
Total collateral (up to and exceeding 100% of the net position)
Derivative [Line Items]
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 574	$ 559