Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 34,200,000,000		$ 19,850,000,000
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans	16,000,000		18,000,000
Aggregate fair value of derivative financial instruments in a liability position	20,000,000		21,000,000
Net liability positions with counterparties	20,000,000		21,000,000
Aggregate fair value of derivative financial instruments in asset position	7,000,000		18,000,000
Net fair value of derivative financial instruments in a net asset position	7,000,000		18,000,000
Collateral relating to net asset positions	3,000,000		16,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	20,000,000		18,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Amount of initial margin posted	71,000,000		65,000,000
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase decrease in net interest income due to interest rate swap agreements	(13,000,000)	$ 1,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	43,300,000,000		42,900,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	832,000,000		$ 763,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Fair value of additional collateral to be posted for derivative financial instruments	$ 0