Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 9,550,000,000		$ 9,400,000,000
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans	17,000,000		16,000,000
Aggregate fair value of derivative financial instruments in a liability position	4,000,000		13,000,000
Net liability positions with counterparties	4,000,000		13,000,000
Aggregate fair value of derivative financial instruments in asset position	38,000,000		13,000,000
Net fair value of derivative financial instruments in a net asset position	38,000,000		13,000,000
Collateral relating to net asset positions	32,000,000		12,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	4,000,000		12,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Amount of initial margin posted	53,000,000		52,000,000
Reduction in the fair value of derivative asset due to contractual settlements	(122,000,000)
Reduction in the fair value of derivative liability due to contractual settlements	(6,000,000)
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	1,000,000	$ 4,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes		39,500,000,000	29,900,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes		$ 538,000,000	$ 530,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Fair value of additional collateral to be posted for derivative financial instruments	$ 0