Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivatives designated as hedging instruments
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 1.1	$ 8.4	$ 15.1
Notional Amount		205.5
Derivatives designated as hedging instruments | Fair Value Hedge | Interest Rate Swaps | Interest expense
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.0)	(8.2)	(14.1)
Derivatives designated as hedging instruments | Cash Flow Hedge
Derivative instruments gain (loss)
Notional Amount	0	0
Derivatives designated as hedging instruments | Cash Flow Hedge | Interest income
Derivative instruments gain (loss)
Amount of gains reclassified from AOCI to Interest	0.1	0.2	1.0
Derivatives designated as hedging instruments | Cash Flow Hedge | Interest Rate Swaps | Interest income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.1	0.2	1.0
Derivatives not designated as hedging instruments
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	28.7	25.5	23.1
Notional Amount	3,499.9	2,719.1
Derivatives not designated as hedging instruments | Interest Rate Contracts
Derivative instruments gain (loss)
Notional Amount	3,024.0	2,487.7
Derivatives not designated as hedging instruments | Interest Rate Contracts | Other noninterest income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	1.0	1.1	(1.1)
Derivatives not designated as hedging instruments | Option contracts | Other noninterest income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.2	(1.7)	0.1
Derivatives not designated as hedging instruments | Foreign Exchange Contracts
Derivative instruments gain (loss)
Notional Amount	474.0	231.4
Derivatives not designated as hedging instruments | Foreign Exchange Contracts | International services income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	27.5	26.1	24.1
Derivatives not designated as hedging instruments | Interest Rate Swaps
Derivative instruments gain (loss)
Notional Amount	2,769.4	2,243.6
Derivatives designated and not designated as hedging instruments
Credit Risk Exposure and Collateral
Aggregate fair value of derivatives with credit-risk-related contingent features, net liability position	0.6
Collateral delivered on swap agreements in the form of securities, with credit-risk-related contingent features	2.5
Collateral delivered on swap agreements in the form of cash, with credit-risk-related contingent features	7.8
Derivatives designated and not designated as hedging instruments | Interest Rate Swaps
Credit Risk Exposure and Collateral
Interest rate swap credit risk exposure	2.4	1.6
Collateral received from swap counterparties	0	0
Collateral delivered on swap agreements, without credit-risk contingent features	$ 9.9