Commitments and Contingencies (Narrative) (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Commitments and Contingencies
Letters of credit and financial guarantees written	$ 5,784,000,000	$ 6,095,000,000
Carrying amount of the liability for letters of credit	33,000,000	27,000,000
Investments in affordable housing and historic building rehabilitation projects	1,100,000,000	1,200,000,000
Commitments to fund affordable housing investments	355,000,000	394,000,000
Outstanding loan commitments for affordable housing and historic rehabilitation projects	191,000,000	178,000,000
Outstanding loan balance for affordable housing and historic rehabilitation projects	70,000,000	76,000,000
Investments in private equity and similar investments	301,000,000	261,000,000
Future funding commitments to private equity and similar investments	$ 114,000,000	$ 129,000,000