Variable Interest Entities (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Variable Interest Entities [Abstract]
Investment securities related to state and political subdivisions	$ 2,720,000,000	$ 2,810,000,000
Variable interest entity, other short-term borrowings	2,180,000,000	2,290,000,000
Weighted Average Life Of Trusts	7 years 1 month 6 days	7 years 4 months 24 days
Total standby bond-purchase agreement committed to trusts	2,220,000,000
Letters of Credit Outstanding, Amount	669,000,000
Number Of Standby Purchase Agreements Utilized	0
Aggregate notional value of CDOs	400,000,000
Carrying value of the underlying collateral	$ 123,000,000	$ 166,000,000