Allowance for Loan Losses and Credit Quality of Loans, Troubled Debt Restructurings (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Financing Receivable, Modifications [Line Items]
Period of sustained repayment performance for nonperforming TDRs to be returned to performing status (in months)	6 months
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	10
Financing receivable modifications recorded investment during period	0.6
Residential Real Estate Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Financing receivable modifications recorded investment during period	0.1