Significant Accounting Policies (Nature of Operations and Basis of Presentation) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Bank partnership	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Minimum Number of Days Past Due as to Interest or Principal Payments in Accruing Loans Moves to Nonperforming Loans	90 days
Nature of Operations and Basis of Presentation
Number of banks through which company operates	1
Number of regional banking units Chemical Bank operates through	4
Significant partner in low income housing tax credit partnership, number of partnerships	3
Investment in qualified affordable housing projects	$ 4.9	$ 3.1
Unfunded obligation amount for variable interest entity	2.0
income tax expense attributable to qualified affordable housing projects	0.4
Percentage of FHLB advances secured by first lien real estate residential loans	145.00%
Minimum percentage of tax benefit is recognized for the amount likely to be realized	50.00%
Reserve for contingent income tax liabilities recorded	$ 0