Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	$ 11,000,000	$ 9,000,000	$ 30,000,000	$ 27,000,000
Notional value of foreign currency and other option and futures contracts entered into for trading purposes	904,000,000		904,000,000		869,000,000
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans			27,000,000		89,000,000
Aggregate fair value of derivative financial instruments in a liability position	229,000,000		229,000,000		374,000,000
Net liability positions with counterparties	132,000,000		132,000,000		281,000,000
Post collateral requirements relating to positions	118,000,000		118,000,000		266,000,000
Fair value of additional collateral to be posted for derivative financial instruments	13,000,000		13,000,000
Aggregate fair value of derivative financial instruments in asset position	187,000,000		187,000,000		164,000,000
Net asset positions with counterparties	98,000,000		98,000,000		71,000,000
Counterparties posted collateral relating to positions	96,000,000		96,000,000		69,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	42,000,000		42,000,000
Fair value of collateral already posted for derivative financial instruments	29,000,000		29,000,000
Interest rate contracts [Member]
Derivative [Line Items]
Notional value of interest rate contracts entered into trading purposes	$ 15,900,000,000		$ 15,900,000,000		$ 15,500,000,000