Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net Unrealized Gain on Securities
Before Tax Reclassification from AOCI for Sales of Securities	$ (3.7)	$ 11.9
After Tax Reclassifications from AOCI for Sales of Securities	(2.4)	7.8
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	10.6	1.2
After Tax Reclassification from AOCI on Derivatives Instruments	6.8	0.8
Unrecognized Pension and Postretirement Benefit Costs
Before Tax Pension Plan Reclassification from AOCI	(1.0)	(13.7)
After Tax Pension Plan Reclassification from AOCI	(0.7)	(9.0)
Net Realized Investments Gain Loss
Net Unrealized Gain on Securities
Before Tax Reclassification from AOCI for Sales of Securities	(3.7)	12.7
Before Tax Reclassification from AOCI for Write-down of Securities	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	2.5	0
Net Realized Investments Gain Loss | Foreign Exchange Contracts
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	(2.1)	(6.7)
Net Investment Income | Interest Rate Swaps
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	11.7	10.0
Net Investment Income | Foreign Exchange Contracts
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	(1.1)	(1.7)
Interest and Debt Expense | Interest Rate Swaps
Net Gain on Cash Flow Hedges
Before Tax Reclassification from AOCI on Derivatives Instruments	(0.4)	(0.4)
Other Expense
Unrecognized Pension and Postretirement Benefit Costs
Before Tax Reclassification from AOCI for Pension Net Actuarial Loss	(1.4)	(14.9)
Before Tax Reclassification from AOCI for Pension Prior Service Credit	0.4	1.2
Income Tax Expense
Net Unrealized Gain on Securities
Income Tax on Reclassifications from AOCI for Sales of Securities	(1.3)	4.1
Net Gain on Cash Flow Hedges
Income Tax on Reclassification from AOCI on Derivatives Instruments	3.8	0.4
Unrecognized Pension and Postretirement Benefit Costs
Income Tax on Pension Plan Reclassification from AOCI	$ (0.3)	$ (4.7)