Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
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	$ 23,000,000		$ 23,000,000		$ 28,000,000
Aggregate fair value of derivative financial instruments in a liability position	96,000,000		96,000,000		161,000,000
Net liability positions with counterparties	91,000,000		91,000,000		103,000,000
Post collateral requirements relating to positions	81,000,000		81,000,000		90,000,000
Aggregate fair value of derivative financial instruments in asset position	40,000,000		40,000,000		104,000,000
Net asset positions with counterparties	35,000,000		35,000,000		46,000,000
Counterparties posted collateral relating to positions	35,000,000		35,000,000		46,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	143,000,000		143,000,000		61,000,000
Aggregate fair value of derivative financial instruments in a net liability position	96,000,000		96,000,000		35,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	17,000,000		17,000,000
Fair value of collateral already posted for derivative financial instruments	11,000,000		11,000,000
Fair value of additional collateral to be posted for derivative financial instruments	6,000,000		6,000,000
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	11,000,000	$ 11,000,000	33,000,000	$ 34,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	17,600,000,000		17,600,000,000		17,600,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 1,600,000,000		$ 1,600,000,000		$ 1,300,000,000