Derivative Financial Instruments Net Realized Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 4.5	$ (166.6)	$ 120.0	$ (211.2)
Other Net Realized Capital Gains (Losses) | Interest rate contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(5.3)	(24.1)	0.7	(53.2)
Other Net Realized Capital Gains (Losses) | Foreign exchange contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(11.7)	16.0	1.2	(0.9)
Other Net Realized Capital Gains (Losses) | Equity contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.7	(1.6)	1.8	(1.3)
Other Net Realized Capital Gains (Losses) | Credit contracts | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	3.6	(19.0)	9.8	(13.0)
Other Net Realized Capital Gains (Losses) | Managed Custody Guarantees | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0	0.8	1.1	1.3
Investment Contract, with a Fixed Maturity | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(4.1)	10.7	(4.3)	9.1
Fixed indexed annuities (FIA) | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	21.3	(149.6)	109.7	(153.2)
Cash Flow Hedging | Other Net Realized Capital Gains (Losses) | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0	0.2	0	0
Fair Value Hedging | Other Net Realized Capital Gains (Losses) | Interest rate contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 0	$ 0	$ 0	$ 0