Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Derivative [Line Items]
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans	$ 22,000,000		$ 18,000,000
Aggregate fair value of derivative financial instruments in a liability position	98,000,000		59,000,000
Net liability positions with counterparties	95,000,000		55,000,000
Post collateral requirements relating to positions	84,000,000		52,000,000
Aggregate fair value of derivative financial instruments in asset position	24,000,000		23,000,000
Net asset positions with counterparties	21,000,000		19,000,000
Counterparties posted collateral relating to positions	21,000,000		22,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	204,000,000		99,000,000
Aggregate fair value of derivative financial instruments in a net liability position	156,000,000		50,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	19,000,000
Fair value of collateral already posted for derivative financial instruments	13,000,000
Fair value of additional collateral to be posted for derivative financial instruments	6,000,000
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	10,000,000	$ 11,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	18,900,000,000		18,400,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 2,800,000,000		$ 1,600,000,000