Loans and Allowance for Loan Losses (Details 7) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Loans by Credit Quality Indicators
Total loans	$ 28,743	$ 28,476
Commercial and Industrial [Member]
Loans by Credit Quality Indicators
Total loans	20,133	19,450
Construction Loans [Member]
Loans by Credit Quality Indicators
Total loans	613	871
Commercial Mortgage [Member]
Loans by Credit Quality Indicators
Total loans	7,997	8,155
Pass [Member]
Loans by Credit Quality Indicators
Total loans	27,300	26,469
Pass [Member] | Commercial and Industrial [Member]
Loans by Credit Quality Indicators
Total loans	19,456	18,594
Pass [Member] | Construction Loans [Member]
Loans by Credit Quality Indicators
Total loans	531	674
Pass [Member] | Commercial Mortgage [Member]
Loans by Credit Quality Indicators
Total loans	7,313	7,201
Criticized [Member]
Loans by Credit Quality Indicators
Total loans	1,443	2,007
Criticized [Member] | Commercial and Industrial [Member]
Loans by Credit Quality Indicators
Total loans	677	856
Criticized [Member] | Construction Loans [Member]
Loans by Credit Quality Indicators
Total loans	82	197
Criticized [Member] | Commercial Mortgage [Member]
Loans by Credit Quality Indicators
Total loans	$ 684	$ 954