Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Unrealized Gain on Securities
Before Tax Reclassification from AOCI for Gain (Loss) on Sales of Securities	$ 0.9	$ 5.7	$ (2.8)	$ 17.6
After Tax Reclassifications from AOCI for Sales of Securities	0.7	3.7	(1.7)	11.5
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	21.7	4.3	32.3	5.5
After Tax Reclassification from AOCI on Derivatives Instruments	16.2	2.8	23.0	3.6
Unrecognized Pension and Postretirement Benefit Costs
Before Tax Pension Plan Reclassification from AOCI	(1.0)	(12.3)	(2.0)	(26.0)
After Tax Pension Plan Reclassification from AOCI	(0.6)	(7.9)	(1.3)	(16.9)
Foreign Exchange Contracts
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	13.1		13.1
Net Realized Investments Gain Loss
Net Unrealized Gain on Securities
Before Tax Reclassification from AOCI for Gain (Loss) on Sales of Securities	0.9	5.7	(2.8)	18.4
Before Tax Reclassification from AOCI for Other-Than-Temporary Impairment of Securities	0	0	0	(0.8)
Net Realized Investments Gain Loss | Interest Rate Swaps
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	0	0.8	2.5	0.8
Net Realized Investments Gain Loss | Foreign Exchange Contracts
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	11.1	(5.7)	9.0	(12.4)
Net Investment Income | Interest Rate Swaps
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	12.2	11.1	23.9	21.1
Net Investment Income | Foreign Exchange Contracts
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	(1.1)	(1.5)	(2.2)	(3.2)
Interest and Debt Expense | Interest Rate Swaps
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	(0.5)	(0.4)	(0.9)	(0.8)
Other Expense
Unrecognized Pension and Postretirement Benefit Costs
Before Tax Reclassification from AOCI for Pension Net Actuarial Loss	(1.4)	(12.9)	(2.8)	(27.8)
Before Tax Reclassification from AOCI for Pension Prior Service Credit	0.4	1.3	0.8	2.5
Before Tax Reclassification from AOCI for Curtailment Loss	0	(0.7)	0	(0.7)
Income Tax Expense
Net Unrealized Gain on Securities
Income Tax on Reclassifications from AOCI for Sales of Securities	0.2	2.0	(1.1)	6.1
Net Gain on Cash Flow Hedges
Income Tax on Reclassification from AOCI on Derivatives Instruments	5.5	1.5	9.3	1.9
Unrecognized Pension and Postretirement Benefit Costs
Income Tax on Pension Plan Reclassification from AOCI	$ (0.4)	$ (4.4)	$ (0.7)	$ (9.1)