Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 D class component M Y segment	Sep. 30, 2011	Dec. 31, 2010
Variable Interest Entities
Period over which tax credits are generally recognized (in years)	10
Investment in variable interest entities	$ 34.3		$ 29.7
Unfunded commitments to fund low-income housing partnerships	9.0		2.6
Loans and Leases
Number of portfolio segments of loans and leases (commercial and consumer)	2
Number of classes of loans and leases determined by management	8
Loans modified in a troubled debt restructuring
Maximum period during which non-accrual loan that has been modified in a troubled debt restructuring remains on non-accrual status (in months)	6
Troubled debt restructuring period (in months)	12
Dollar amount of loans newly considered trouble debt restructurings		$ 0.5
Number of components of company's reserve for credit losses	2
Cash and Cash Equivalents
Maximum original maturity period of cash and cash equivalents (in days)	90
Commercial and Industrial
Loan and lease portfolio
Minimum maturity period to be considered to place loans and leases on non-accrual status (in days)	90
Minimum maturity period to be considered for loans and leases to be charged off (in days)	120
Residential Mortgage and Home Equity
Loan and lease portfolio
Minimum maturity period to be considered for loans and leases to be charged off (in days)	120
Home Equity
Loan and lease portfolio
Minimum maturity period to be considered for loans and leases to be charged off (in days)	120
Home Equity | Maximum
Loan and lease portfolio
Combined loan-to-value ratio, considered in determining whether the entire outstanding balance on the loan is to be charged-off or not (as a percent)	60.00%
Automobile and Other consumer
Loan and lease portfolio
Minimum maturity period to be considered for loans and leases to be charged off (in days)	120