Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net Realized Investment Gain (Loss), Excluding Other-Than-Temporary Impairment Loss on Fixed Maturity Securities									$ 29.6	$ 7.6	$ 56.2
Other than Temporary Impairment Losses									(13.5)	(0.8)	0
Net Investment Income	629.4	606.4	629.1	612.5	629.4	615.5	626.1	621.1	2,477.4	2,492.1	2,515.2
Interest and Debt Expense									(167.5)	(149.4)	(145.4)
Other Cost and Expense, Operating									(831.2)	(751.5)	(782.9)
Income Before Income Tax	(457.9)	312.1	346.5	326.5	305.8	284.1	311.5	303.8	527.2	1,205.2	1,249.5
Income Tax Expense (Benefit)									113.8	347.1	355.1
Net Income	(279.1)	221.1	242.5	228.9	221.2	205.7	218.6	212.6	413.4	858.1	894.4
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gain on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net Realized Investment Gain (Loss), Excluding Other-Than-Temporary Impairment Loss on Fixed Maturity Securities									12.6	(12.6)
Other than Temporary Impairment Losses									(13.5)	(0.8)
Income Before Income Tax									(0.9)	(13.4)
Income Tax Expense (Benefit)									(0.6)	(4.8)
Net Income									(0.3)	(8.6)
Reclassification out of Accumulated Other Comprehensive Income | Net Gain on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income Before Income Tax									53.0	23.0
Income Tax Expense (Benefit)									16.6	8.0
Net Income									36.4	15.0
Reclassification out of Accumulated Other Comprehensive Income | Net Gain on Cash Flow Hedges | Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net Realized Investment Gain (Loss), Excluding Other-Than-Temporary Impairment Loss on Fixed Maturity Securities									4.3	1.3
Net Investment Income									47.8	43.1
Interest and Debt Expense									(1.8)	(1.7)
Reclassification out of Accumulated Other Comprehensive Income | Net Gain on Cash Flow Hedges | Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net Realized Investment Gain (Loss), Excluding Other-Than-Temporary Impairment Loss on Fixed Maturity Securities									6.9	(13.8)
Net Investment Income									(4.2)	(5.9)
Reclassification out of Accumulated Other Comprehensive Income | Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Cost and Expense, Operating									(5.6)	(32.9)
Reclassification out of Accumulated Other Comprehensive Income | Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Cost and Expense, Operating									1.7	5.0
Reclassification out of Accumulated Other Comprehensive Income | Pension Curtailment Gain
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Cost and Expense, Operating									0	3.0
Reclassification out of Accumulated Other Comprehensive Income | Pension Settlement Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Cost and Expense, Operating									(64.4)	0
Reclassification out of Accumulated Other Comprehensive Income | Unrecognized Pension and Postretirement Benefit Costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income Before Income Tax									(68.3)	(24.9)
Income Tax Expense (Benefit)									(23.8)	(8.9)
Net Income									$ (44.5)	$ (16.0)