Financial Instruments Derivative Net Realized Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets	$ 532.3		$ 532.3		$ 446.6
Derivative Liabilities	363.0		363.0		360.1
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(15.6)	(31.6)	115.5	(44.6)
Not Designated as Hedging Instrument [Member] | Interest rate contracts | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	28.9	(23.3)	6.0	(29.4)
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	12.5	(8.7)	12.9	(16.9)
Not Designated as Hedging Instrument [Member] | Equity contract | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.5)	0.1	1.1	0.4
Not Designated as Hedging Instrument [Member] | Credit contracts
Derivative Instruments, Gain (Loss) [Line Items]
Maximum Potential Future Exposure on Credit Risk Derivatives	339.0		339.0		518.3
Not Designated as Hedging Instrument [Member] | Credit contracts | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.6)	1.2	6.2	6.0
Not Designated as Hedging Instrument [Member] | Managed Custody Guarantees [Member] | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0	0.5	1.1	0.5
Investment Contract, with a Fixed Maturity | Not Designated as Hedging Instrument [Member] | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	4.6	5.7	(0.2)	(1.6)
Fixed indexed annuities (FIA) | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets	0		0		0
Derivative Liabilities	150.6		150.6		236.3
Fixed indexed annuities (FIA) | Not Designated as Hedging Instrument [Member] | Other Net Realized Capital Gains (Losses) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(59.5)	(7.1)	88.4	(3.6)
Other liabilities | Not Designated as Hedging Instrument [Member] | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities	337.7		337.7		306.4
Other liabilities | Not Designated as Hedging Instrument [Member] | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities	23.6		23.6		32.4
Other liabilities | Not Designated as Hedging Instrument [Member] | Equity contract
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities	0		0		0
Other liabilities | Not Designated as Hedging Instrument [Member] | Credit contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities	$ 1.7		$ 1.7		$ 21.3