Other Comprehensive Income And Accumulated Other Comprehensive Income Reclassification from AOCI to Consolidated Statements of 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 [Line Items]
Net Realized Gains (Losses) on Sales of Investments	$ 21.0	$ 8.0	$ 3.5	$ 6.6	$ 20.8	$ 49.1	$ 2.3	$ 26.9	$ 39.1	$ 99.1	$ 65.4
Net Impairment Losses Recognized in Earnings	(6.5)	(3.8)	(4.1)	(0.8)	(7.6)	(3.4)	(1.0)	(1.9)	(15.2)	(13.9)	(6.9)
Income Tax Benefit (Expense)	(29.8)	0.8	(1.9)	(16.7)	(26.6)	(33.4)	(13.9)	(26.0)	(47.6)	(99.9)	(30.6)
Net Income	65.4	4.7	9.3	35.1	55.2	70.1	34.0	58.4	114.5	217.7	103.4
Interest and Other Expenses	(24.4)	(22.1)	(22.5)	(22.7)	(26.2)	(25.3)	(25.2)	(23.8)	(91.7)	(100.5)	(85.5)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income									11.2	8.5	29.2
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains (Losses) on Sales of Investments									37.9	51.8	65.0
Net Impairment Losses Recognized in Earnings									(12.8)	(13.9)	(3.8)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest									25.1	37.9	61.2
Income Tax Benefit (Expense)									(8.8)	(13.2)	(21.5)
Net Income									16.3	24.7	39.7
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Benefit (Expense)									2.8	8.8	5.7
Net Income									(5.1)	(16.2)	(10.5)
Interest and Other Expenses									$ (7.9)	$ (25.0)	$ (16.2)