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Pension and Other Postretirement Benefit Plans (Textual) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Contribution to corporation's pension plan [Member]
       
Defined Benefit Plan Disclosure [Line Items]        
Contribution to defined benefit pension plan     $ 15.0  
Pension Plans, Defined Benefit [Member]
       
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate     4.08%  
Chemical Financial Corporation [Member]
       
Defined Benefit Plan Disclosure [Line Items]        
Percentage of eligible pay contribution to certain employees     4.00%  
Defined Contribution Plan, Employer Total Contribution Amount $ 0.9 $ 0.8 $ 2.7 $ 2.3