Business Combinations (Narrative) (Details) (USD $)	12 Months Ended		0 Months Ended	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Apr. 15, 2013	Jun. 30, 2013	Apr. 12, 2013 Branch	Feb. 04, 2013
Business Combinations [Line Items]
Assets	$ 24,902,347,000	$ 23,912,028,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	0
Deferred Tax Assets, Net	289,082,000	331,050,000
Business Combination, Acquisition Related Costs	1,000,000	75,100,000
Citizens Republic Bancorp
Business Combinations [Line Items]
Assets					9,600,000,000
Number of Branches					219
Business Acquisition, Equity Interest Issued or Issuable, Share Conversion Ratio					1.37
Amount of Citizens TARP Preferred Stock					300,000,000
Accumulated but unpaid interest and dividends related to Citizens TARP Preferred Stock					55,400,000
Debt Instrument, Face Amount						250,000,000
Debt Instrument, Interest Rate, Stated Percentage						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%
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Noncurrent					313,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent					51,300,000
Deferred Tax Assets, Net					261,700,000
Net Operating Loss and Tax Credit Carryforwards included in Acquired Deferred Tax Asset					224,800,000
Business combination, deferred tax asset fair market value adjustment					87,600,000
Deferred tax changes reflected in acquired net assets	0	(348,239,000)			349,300,000
Acquired Receivables, Fair Value					4,617,004,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities					3,202,575,000
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			652,500,000
Federal home loan bank advances retained	66,800,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Subordinated Debt					74,500,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Long Term Repurchase Agreements					115,000,000
FirstMerit | Citizens Republic Bancorp
Business Combinations [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	2,549,701.61				2,408,203
Citizens Republic Bancorp | Citizens Republic Bancorp
Business Combinations [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights					1,757,812.5
Acquired performing loans | Citizens Republic Bancorp
Business Combinations [Line Items]
Acquired Receivables, Fair Value					3,797,289,000
Acquired Impaired Loans | Citizens Republic Bancorp
Business Combinations [Line Items]
Acquired Receivables, Fair Value					819,715,000
Acquired Impaired Loans | Citizens Republic Bancorp
Business Combinations [Line Items]
Acquired Receivables, Fair Value					$ 1,100,000,000
VIE 2
Business Combinations [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.10%
London Interbank Offered Rate (LIBOR) [Member] | Maximum | Junior Subordinated Debt | Citizens Republic Bancorp
Business Combinations [Line Items]
Debt Instrument, Basis Spread on Variable Rate		11.75%
London Interbank Offered Rate (LIBOR) [Member] | VIE 2
Business Combinations [Line Items]
Debt Instrument, Description of Variable Rate Basis		LIBOR