Derivative Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	$ 18,000,000	$ 28,000,000
Aggregate fair value of derivative financial instruments in a liability position	59,000,000	161,000,000
Net liability positions with counterparties	55,000,000	103,000,000
Post collateral requirements relating to positions	52,000,000	90,000,000
Aggregate fair value of derivative financial instruments in asset position	23,000,000	104,000,000
Net asset positions with counterparties	19,000,000	46,000,000
Counterparties posted collateral relating to positions	22,000,000	46,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	99,000,000	61,000,000
Aggregate fair value of derivative financial instruments in a net liability position	50,000,000	35,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	13,000,000
Fair value of collateral already posted for derivative financial instruments	6,000,000
Fair value of additional collateral to be posted for derivative financial instruments	7,000,000
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	44,000,000	45,000,000	$ 41,000,000
Average notional amounts of interest rate swap agreements impacting net interest income, contract entered into for interest rate risk management purposes	1,400,000,000	1,400,000,000	$ 1,200,000,000
Notional amounts of derivative contracts entered into for trading account purposes	1,400,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	18,400,000,000	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	$ 1,300,000,000