Variable Interest Entities (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Variable Interest Entities [Abstract]
Investment securities related to state and political subdivisions	$ 2,750,000,000	$ 2,810,000,000
Variable interest entity, other short-term borrowings	2,250,000,000	2,290,000,000
Weighted-average life of trusts, years	7.3	7.4
Total standby bond-purchase agreement committed to trusts	2,300,000,000
Letters of Credit Outstanding, Amount	669,000,000
Number Of Standby Purchase Agreements Utilized	0
Aggregate notional value of CDOs	400,000,000	400,000,000
Carrying value of the underlying collateral	$ 154,000,000	$ 166,000,000