Derivative Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 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	16,000,000	$ 28,000,000
Aggregate fair value of derivative financial instruments in a liability position	13,000,000	34,000,000
Net liability positions with counterparties	13,000,000	30,000,000
Aggregate fair value of derivative financial instruments in asset position	13,000,000	15,000,000
Net fair value of derivative financial instruments in a net asset position	13,000,000	11,000,000
Collateral relating to net asset positions	12,000,000	9,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	12,000,000	27,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Net fair value of derivative financial instruments in a net asset position	2,000,000	63,000,000
Collateral relating to net asset positions	2,000,000	81,000,000
Amount of initial margin posted	52,000,000	111,000,000
Reduction in the fair value of derivative asset due to contractual settlements	(136,000,000)
Reduction in the fair value of derivative liability due to contractual settlements	(70,000,000)
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	25,000,000	37,000,000	$ 44,000,000
Notional amounts of derivative contracts entered into for trading account purposes	9,400,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	29,900,000,000	21,600,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	530,000,000,000	$ 471,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Fair value of additional collateral to be posted for derivative financial instruments	0
Credit Risk Derivative [Member] | Maximum [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	$ 1,000,000