Commitments and Contingencies (Narrative) (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Letters of credit and financial guarantees written	$ 5,939,000,000	$ 6,095,000,000
Carrying amount of the liability for letters of credit	37,000,000	27,000,000
Investments in affordable housing and historic building rehabilitation projects	1,200,000,000	1,200,000,000
Commitments to fund affordable housing investments	383,000,000	394,000,000
Outstanding loan commitments for affordable housing and historic rehabilitation projects	180,000,000	178,000,000
Outstanding loan balance for affordable housing and historic rehabilitation projects	63,000,000	76,000,000
Maximum risk exposure related to affordable housing and historic rehabilitation projects	1,400,000,000	1,400,000,000
Investments in venture capital funds	281,000,000	261,000,000
Future funding commitments to venture capital funds	$ 119,000,000	$ 129,000,000