Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 47,400,000,000		$ 47,400,000,000		$ 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	24,000,000		24,000,000		18,000,000
Aggregate fair value of derivative financial instruments in a liability position	70,000,000		70,000,000		21,000,000
Net liability positions with counterparties	70,000,000		70,000,000		21,000,000
Aggregate fair value of derivative financial instruments in asset position	639,000		639,000		18,000,000
Net fair value of derivative financial instruments in a net asset position	639,000		639,000		18,000,000
Collateral relating to net asset positions	81,000		81,000		16,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	68,000,000		68,000,000		18,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Amount of initial margin posted	129,000,000		129,000,000		65,000,000
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase decrease in net interest income due to interest rate swap agreements	(1,000,000)	$ (8,000,000)	(23,000,000)	$ (12,000,000)
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	47,600,000,000		47,600,000,000		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	843,000,000		843,000,000		$ 763,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Fair value of additional collateral to be posted for derivative financial instruments	$ 0		$ 0