Schedule of Reclassifications from Accumulated Other Comprehensive Income to Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Unrealized Gain on Securities Reclassified to Net Income
Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	$ 4.1
Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	7.8
Gain on Cash Flow Hedges Reclassified to Net Income
Reclassification Adjustment on Derivatives Included in Net Income, before Tax	1.2
Reclassification Adjustment on Derivatives Included in Net Income, Tax	0.4
Cash Flow Hedge Gain Reclassified to Earnings, Net	0.8
Unrecognized Pension and Postretirement Benefit Costs Reclassified to Net Income
Total Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	(13.7)
Reclassification Adjustment for Pension and Other Postretirement Benefit Plans, Net (Loss) Recognized in Net Periodic Benefit Cost, Tax	(4.7)
Reclassification Adjustment on Pension and Other Postretirement Benefit Plans, Net Loss Recognized in Net Periodic Benefit Cost, Net of Tax	(9.0)
Net Realized Investments Gain Loss [Member]
Unrealized Gain on Securities Reclassified to Net Income
Reclassification Adjustment for Sale of Securities Included in Net Income, before Tax	11.9
Other Expense [Member]
Unrecognized Pension and Postretirement Benefit Costs Reclassified to Net Income
Reclassification Adjustment on Pension and Other Postretirement Benefit Plans for Amortization of Net Actuarial Loss, before Tax	(14.9)
Amortization of Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	1.2
Interest Rate Swap [Member]
Gain on Cash Flow Hedges Reclassified to Net Income
Cash Flow Hedge Gain Reclassified to Net Investment Income	10.0
Cash Flow Hedge Loss Reclassified to Interest and Debt Expense	(0.4)
Foreign Exchange Contract [Member]
Gain on Cash Flow Hedges Reclassified to Net Income
Cash Flow Hedge Gain Reclassified to Net Investment Income	(1.7)
Foreign Exchange Contract [Member] | Net Realized Investments Gain Loss [Member]
Gain on Cash Flow Hedges Reclassified to Net Income
Cash Flow Hedge Loss Reclassified to Earnings	$ (6.7)