Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives designated as hedging instruments
Derivative
Notional Amount	$ 205.5	$ 207.4
Derivative Assets	2.2	9.8
Derivatives designated as hedging instruments | Deposits and borrowings
Derivative
Derivative Assets	1.1	8.8
Derivatives designated as hedging instruments | Fair Value Hedge | Interest Rate Swaps
Derivative
Mark-to-market asset	1.1	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	2.2	9.8
Derivatives not designated as hedging instruments
Derivative
Notional Amount	2,719.1	1,957.0
Derivative Assets	66.6	54.5
Derivative Liabilities	65.7	55.0
Derivatives not designated as hedging instruments | Interest Rate Contracts
Derivative
Notional Amount	2,487.7	1,753.2
Derivative Assets	64.4	51.7
Derivative Liabilities	64.4	52.9
Derivatives not designated as hedging instruments | Interest Rate Swaps
Derivative
Notional Amount	2,243.6	1,482.1
Derivative Assets	64.0	51.3
Derivative Liabilities	64.0	52.5
Derivatives not designated as hedging instruments | Interest Rate Caps, Floors and Collars
Derivative
Notional Amount	240.1	267.1
Derivative Assets	0.2	0.3
Derivative Liabilities	0.2	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	0.7	0.7
Derivatives not designated as hedging instruments | Spot and forward contracts
Derivative
Notional Amount	231.4	203.8
Derivative Assets	1.5	2.1
Derivative Liabilities	$ 1.3	$ 2.1