Business Combinations (Details) (USD $)				0 Months Ended		3 Months Ended		6 Months Ended			6 Months Ended					3 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Apr. 15, 2013 Citizens Republic Bancorp	Apr. 12, 2013 Citizens Republic Bancorp	Jun. 30, 2013 Citizens Republic Bancorp Branch	Jun. 30, 2013 Citizens Republic Bancorp Branch	Jun. 30, 2013 Citizens Republic Bancorp Branch	Feb. 04, 2013 Citizens Republic Bancorp	Sep. 12, 2012 Citizens Republic Bancorp	Jun. 30, 2013 Citizens Republic Bancorp Junior Subordinated Debt	Jun. 30, 2013 Citizens Republic Bancorp Junior Subordinated Debt Minimum	Jun. 30, 2013 Citizens Republic Bancorp Junior Subordinated Debt Maximum	Apr. 12, 2013 FirstMerit [Member] Citizens Republic Bancorp	Apr. 12, 2013 Citizens Republic Bancorp	Jun. 30, 2013 Michigan and Wisconsin Citizens Republic Bancorp	Apr. 12, 2013 Acquired Loans [Member]	Jun. 30, 2013 Federal Home Loan Bank Advance 1 Citizens Republic Bancorp	Jun. 30, 2013 Federal Home Loan Bank Advance 2 Citizens Republic Bancorp	Apr. 12, 2013 Acquired Non-impaired Acquired Loans [Member]
Business Combinations [Line Items]
Assets	$ 23,532,129,000	$ 14,913,012,000	$ 14,621,344,000							$ 9,594,645,000
Accumulated but unpaid interest and dividends related to Citizens TARP Preferred Stock					55,400,000
Number of Branches						219	219	219
Business Acquisition, Equity Interest Issued or Issuable, Share Conversion Ratio					1.37
Stock issued for Citizens acquisition					55,468,283
Amount of Citizens TARP Preferred Stock					300,000,000
Debt Instrument, Face Amount									250,000,000
Interest Rate subordinated notes									4.35%
Total gross proceeds from issuance of depositary shares									100,000,000
Interest rate of Non-Cumulative Perpetual Preferred Stock, Series A									5.875%
Class of Warrant or Right, Number of Securities Called by Warrants or Rights														2,408,203	1,757,812.5
Goodwill					274,338,000
Business Acquisition, Purchase Price Allocation, deferred tax asset					312,900,000.0
Business Acquisition, Purchase Price Allocation, Deferred Taxes Asset (Liability), Net, Noncurrent					83,200,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deferred Tax Asset, Net					344,800,000
Business Acquisition, Purchase Price Allocation, Deferred Tax Liabilities, Noncurrent					51,300,000.0
Deferred Tax Assets, Net					261,600,000.0
Net Operating Loss and Tax Credit Carryforwards included in Acquired Deferred Tax Liability					224,700,000
Days subsequent to acquisition							79 days
Interest Income, Operating																80,300,000.0
Net Income (Loss) Attributable to Parent																20,800,000.0
Business Combination, Acquisition Related Costs							29,300,000	32,900,000
Acquired Non-impaired																				3,851,491,000
Contractual required payments receivable																	5,101,836,000			4,078,355,000
Nonaccretable difference																	(121,719,000)			0
Investment Securities					3,202,577,000
Amount of securities sold subsequent to acquisition						2,200,000,000
Repurchase of securities subsequent to acquisition						1,500,000,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Federal Home Loan Bank Advances					719,300,000
Repayments of Federal Home Loan Bank Borrowings				591,900,000
Prepayment penalties on federal home loan bank advances					60,600,000
Federal home loan bank advances retained						60,000,000	60,000,000	60,000,000
Prepayment penalties on Federal Home Loan Bank Advances Retained						5,600,000	5,600,000	5,600,000
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate																		3.29%	3.39%
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Subordinated Debt					74,500,000
Debt Instrument, Description of Variable Rate Basis											LIBOR
Debt Instrument, Basis Spread on Variable Rate												3.10%	11.75%
Debt Instrument, Interest Rate, Stated Percentage											7.50%
Business Combination Recognized Identifiable Assets Acquired And Liabilities Long Term Repurchase Agreements					$ 115,000,000