Derivative Financial Instruments Notional and Fair Values (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 543.7	$ 446.6
Derivative Liabilities	380.0	360.1
Derivative Asset, Fair Value, Gross Asset	598.6	505.8
Derivative Asset, Fair Value, Gross Liability	510.5	597.4
Interest rate contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	16,353.3	17,555.1
Interest rate contracts | Not Designated as Hedging Instrument | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	346.4	306.4
Interest rate contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	319.3	269.4
Foreign exchange contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	213.4	213.4
Foreign exchange contracts | Not Designated as Hedging Instrument | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	32.9	32.4
Foreign exchange contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	0.4	0.7
Equity contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	10.3	0
Equity contract | Not Designated as Hedging Instrument | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	0.1	0
Equity contract | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Credit contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	359.5	548.4
Maximum Potential Future Exposure on Credit Risk Derivatives	339.0	518.3
Credit contracts | Not Designated as Hedging Instrument | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	0.6	21.3
Credit contracts | Not Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	2.8	2.6
Managed Custody Guarantees | Not Designated as Hedging Instrument | Future Policy Benefits and Claims Reserves
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	0	1.0
Cash Flow Hedging | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,000.0	1,000.0
Cash Flow Hedging | Interest rate contracts | Designated as Hedging Instrument | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	0	0
Cash Flow Hedging | Interest rate contracts | Designated as Hedging Instrument | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	221.2	173.9
Fixed maturities | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Assets	54.9	59.2
Derivative Liabilities	0	0
Fixed indexed annuities (FIA) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	$ 130.5	$ 236.3