Derivatives (Derivative Financial Instruments - Additional Information) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative
Valuation adjustments related to the credit risk associated with counterparties of customer accomodation derivative contracts	$ 10,000,000	$ 3,000,000
Notional amount of the risk participation agreements	4,809,000,000	4,002,000,000
Amount of variation margin payment applied to derivative asset contracts	345,000,000	249,000,000
Amount of variation margin payment applied to derivative liability contracts	33,000,000	23,000,000
Total collateral
Derivative
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	524,000,000	481,000,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 779,000,000	551,000,000
Interest Rate Contract | Credit Risk
Derivative
Credit Risk Derivatives Average Remaining Life	3 years 4 months 24 days
Fair value of risk participation agreements	$ 9,000,000	8,000,000
Interest Rate Contract | Cash Flow Hedging
Derivative
Maximum length of time hedged in cash flow hedge	5 years 10 months
Deferred gains or losses, net of tax, on cash flow hedges were recorded in accumulated other comprehensive income	$ 249,000,000	$ 160,000,000
Net deferred gains or losses, net of tax, recorded in accumulated other comprehensive income are expected to be reclassified into earnings during the next twelve months	$ 12,000,000