Derivative financial instruments (Details Textual) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Derivative financial instruments (Textual) [Abstract]
Increase in net interest income due to interest rate swap agreements	$ 9,000,000	$ 9,000,000	$ 18,000,000	$ 19,000,000
Aggregate fair value of derivative financial instruments in a net liability position	329,000,000		329,000,000
Fair value of collateral posted for derivative financial instruments	303,000,000		303,000,000
Additional derivative financial instruments (Textual) [Abstract]
Notional value of foreign currency and other option and future contracts entered into trading purposes	1,400,000,000		1,400,000,000		1,400,000,000
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans			43,000,000		12,000,000
Fair value of Additional collateral to be posted for derivative financial instruments	69,000,000		69,000,000
Maximum amount of additional collateral required to post to counterparties	29,000,000		29,000,000
Interest rate swap counterparty collateral postings	69,000,000		69,000,000
Interest rate contracts [Member]
Derivative financial instruments (Textual) [Abstract]
Notional value of interest rate contracts entered into trading purposes	15,000,000,000		15,000,000,000		13,900,000,000
Credit Risk Derivative [Member]
Derivative financial instruments (Textual) [Abstract]
Aggregate fair value of derivative financial instruments in a net liability position	$ 98,000,000		$ 98,000,000