Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 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	$ 28,000,000		$ 28,000,000		$ 18,000,000
Aggregate fair value of derivative financial instruments in a liability position	113,000,000		113,000,000		59,000,000
Net liability positions with counterparties	108,000,000		108,000,000		55,000,000
Post collateral requirements relating to positions	102,000,000		102,000,000		52,000,000
Aggregate fair value of derivative financial instruments in asset position	14,000,000		14,000,000		23,000,000
Net asset positions with counterparties	9,000,000		9,000,000		19,000,000
Counterparties posted collateral relating to positions	9,000,000		9,000,000		22,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	280,000,000		280,000,000		99,000,000
Aggregate fair value of derivative financial instruments in a net liability position	212,000,000		212,000,000		50,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	21,000,000		21,000,000
Fair value of collateral already posted for derivative financial instruments	17,000,000		17,000,000
Fair value of additional collateral to be posted for derivative financial instruments	4,000,000		4,000,000
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	20,000,000	$ 22,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	20,100,000,000		20,100,000,000		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	$ 826,000,000		$ 826,000,000		$ 1,600,000,000