Commitments and Contingencies (Narrative) (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Carrying amount of the liability for letters of credit	$ 42,000,000	$ 41,000,000
Investments in affordable housing and historic building rehabilitation projects	1,200,000,000	1,200,000,000
Commitments to fund affordable housing investments	296,000,000	334,000,000
Outstanding loan commitments for affordable housing and historic rehabilitation projects	187,000,000	135,000,000
Outstanding loan balance for affordable housing and historic rehabilitation projects	63,000,000	36,000,000
Maximum risk exposure related to affordable housing and historic rehabilitation projects	1,300,000,000	1,300,000,000
Investments in venture capital funds	247,000,000	266,000,000
Future funding commitments	159,000,000	185,000,000
Notional/Contract Amount [Member]
Standby and commercial letters of credit	6,387,000,000	7,291,000,000
Commitments to fund affordable housing investments	296,000,000	334,000,000
Fair Value [Member]
Standby and commercial letters of credit	42,000,000	41,000,000
Commitments to fund affordable housing investments	$ 280,000,000	$ 316,000,000