Allowance for Loan Losses and Credit Quality of Loans, Troubled Debt Restructurings (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Contract	Dec. 31, 2013 Contract
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		4
Pre-modification outstanding recorded investment		$ 7.0
Number of contracts, subsequent default		1
Outstanding recorded investment, subsequent default		0.9
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	23
Pre-modification outstanding recorded investment	0.3	1.0
Number of contracts, subsequent default	1	8
Outstanding recorded investment, subsequent default	0.1	0.4
Residential Real Estate Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	27	6
Pre-modification outstanding recorded investment	2.7	0.5
Number of contracts, subsequent default	6
Outstanding recorded investment, subsequent default	0.4
Business Banking [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3
Pre-modification outstanding recorded investment	0.9
Indirect Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Pre-modification outstanding recorded investment	0.1
Number of contracts, subsequent default	1
Outstanding recorded investment, subsequent default	0.1
Direct Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	47
Pre-modification outstanding recorded investment	3.0
Number of contracts, subsequent default	5
Outstanding recorded investment, subsequent default	$ 0.2

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524

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Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953682-111524

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

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