Financial Instruments Derivative Notional and Fair Values (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 532.3	$ 446.6
Derivative Liabilities	363.0	360.1
Derivative Asset, Fair Value, Gross Asset	591.2	505.8
Derivative Asset, Fair Value, Gross Liability	513.6	597.4
Interest rate contracts | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	15,364.5	17,555.1
Interest rate contracts | Not Designated as Hedging Instrument [Member] | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	337.7	306.4
Interest rate contracts | Not Designated as Hedging Instrument [Member] | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	314.1	269.4
Foreign exchange contracts | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	213.4	213.4
Foreign exchange contracts | Not Designated as Hedging Instrument [Member] | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	23.6	32.4
Foreign exchange contracts | Not Designated as Hedging Instrument [Member] | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	2.7	0.7
Equity contract | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	13.9	0
Equity contract | Not Designated as Hedging Instrument [Member] | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	0	0
Equity contract | Not Designated as Hedging Instrument [Member] | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	0.4	0
Credit contracts | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	362.7	548.4
Credit contracts | Not Designated as Hedging Instrument [Member] | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	1.7	21.3
Credit contracts | Not Designated as Hedging Instrument [Member] | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	1.1	2.6
Managed Custody Guarantees [Member] | Not Designated as Hedging Instrument [Member] | Future Policy Benefits and Claims Reserves
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	0	1.0
Cash Flow Hedging [Member] | Interest rate contracts | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,000.0	1,000.0
Cash Flow Hedging [Member] | Interest rate contracts | Designated as Hedging Instrument [Member] | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative Liabilities	0	0
Cash Flow Hedging [Member] | Interest rate contracts | Designated as Hedging Instrument [Member] | Derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	214.0	173.9
Fixed maturities | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	58.9	59.2
Derivative Liabilities	0	0
Fixed indexed annuities (FIA) | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	$ 150.6	$ 236.3