Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives designated as hedging instruments
Derivative
Notional Amount	$ 205.5	$ 207.4
Derivative Assets	4.2	9.8
Derivatives designated as hedging instruments | Deposits and borrowings
Derivative
Derivative Assets	3.1	8.8
Derivatives designated as hedging instruments | Fair Value Hedge | Interest Rate Swaps
Derivative
Mark-to-market asset	3.1	8.8
Net interest receivable	1.1	1.0
Derivatives designated as hedging instruments | Fair Value Hedge | Interest Rate Swaps | Long-term and subordinated debt
Derivative
Notional Amount	205.5	207.4
Derivative Assets	4.2	9.8
Derivatives not designated as hedging instruments
Derivative
Notional Amount	2,480.1	1,957.0
Derivative Assets	68.2	54.5
Derivative Liabilities	68.3	55.0
Derivatives not designated as hedging instruments | Interest Rate Contracts
Derivative
Notional Amount	2,177.8	1,753.2
Derivative Assets	65.0	51.7
Derivative Liabilities	66.6	52.9
Derivatives not designated as hedging instruments | Interest Rate Swaps
Derivative
Notional Amount	1,963.1	1,482.1
Derivative Assets	64.7	51.3
Derivative Liabilities	66.3	52.5
Derivatives not designated as hedging instruments | Interest Rate Caps, Floors and Collars
Derivative
Notional Amount	210.7	267.1
Derivative Assets	0.1	0.3
Derivative Liabilities	0.1	0.3
Derivatives not designated as hedging instruments | Options purchased
Derivative
Notional Amount	2.0	2.0
Derivative Assets	0.2	0.1
Derivative Liabilities	0.2	0.1
Derivatives not designated as hedging instruments | Options written
Derivative
Notional Amount	2.0	2.0
Derivatives not designated as hedging instruments | Option contracts
Derivative
Derivative Assets	1.3	0.7
Derivatives not designated as hedging instruments | Foreign Exchange Contracts
Derivative
Notional Amount	302.3	203.8
Derivative Assets	1.9	2.1
Derivative Liabilities	1.7	2.1
Derivatives not designated as hedging instruments | Spot and forward contracts
Derivative
Notional Amount	298.5	203.8
Derivative Assets	1.8	2.1
Derivative Liabilities	1.6	2.1
Derivatives not designated as hedging instruments | Foreign exchange options purchased
Derivative
Notional Amount	1.9
Derivatives not designated as hedging instruments | Foreign exchange options written
Derivative
Notional Amount	1.9
Derivative Assets	0.1
Derivative Liabilities	$ 0.1