Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	$ 10,000,000	$ 9,000,000	$ 19,000,000	$ 18,000,000
Notional value of foreign currency and other option and futures contracts entered into for trading purposes	995,000,000		995,000,000		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			55,000,000		89,000,000
Aggregate fair value of derivative financial instruments in a liability position	241,000,000		241,000,000		374,000,000
Net liability positions with counterparties	145,000,000		145,000,000		281,000,000
Post collateral requirements relating to positions	134,000,000		134,000,000		266,000,000
Fair value of additional collateral to be posted for derivative financial instruments	14,000,000		14,000,000
Aggregate fair value of derivative financial instruments in asset position	218,000,000		218,000,000		164,000,000
Net asset positions with counterparties	82,000,000		82,000,000		71,000,000
Counterparties posted collateral relating to positions	81,000,000		81,000,000		69,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	50,000,000		50,000,000
Fair value of collateral already posted for derivative financial instruments	36,000,000		36,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional value of interest rate contracts entered into trading purposes	$ 15,400,000,000		$ 15,400,000,000		$ 15,500,000,000