Benefit Plans (Narratives) (Details)		12 Months Ended
	May. 13, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jan. 01, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Pension plan transition contribution		$ 900,000	$ 700,000
Employer limit to medical contributions, percent		200.00%
Age limit for subsidized retiree coverage		65
Sunset period of subsidized coverage		3 years
Participating executive election to defer, percent		1.00%
Noncurrent deferred compensation liability		$ 18,600,000	$ 19,000,000
Employer matching contribution, percent of match for first three percent		100.00%	100.00%
Employer matching contribution, percent of match for subsequent two percent		50.00%	50.00%
Repurchase of common stock warrant	$ (12,200,000)	$ (12,150,000)	$ 0	$ 0
Postretirement Life Insurance | Subsequent Event | Maximum
Defined Benefit Plan Disclosure [Line Items]
Amended life insurance cap					$ 10,000
FirstMerit | Savings Plan, 401k
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		7,600,000	$ 7,700,000	$ 4,400,000
Citizens Republic Bancorp | Savings Plan, 401k
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 1,100,000
Employer matching contribution, percent of match for first two percent		50.00%
Employer matching contribution, percent of match for subsequent six percent		25.00%