Other Comprehensive Income (Loss) And Accumulated Other Comprehensive Income Reclassification from AOCI to Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains (Losses) on Sales of Investments	$ 9.4	$ 5.3	$ 34.0	$ 3.4	$ 21.0	$ 8.0	$ 3.5	$ 6.6	$ 52.1	$ 39.1	$ 99.1
Net Impairment Losses Recognized in Earnings	(14.7)	(3.3)	(2.2)	(7.0)	(6.5)	(3.8)	(4.1)	(0.8)	(27.2)	(15.2)	(13.9)
Income Tax Benefit (Expense)	2.9	(11.8)	(6.9)	(4.3)	(29.8)	0.8	(1.9)	(16.7)	(20.1)	(47.6)	(99.9)
Net Income	4.6	37.9	29.7	13.5	65.4	4.7	9.3	35.1	85.7	114.5	217.7
Interest and Other Expenses	$ (25.6)	$ (25.7)	$ (26.6)	$ (29.7)	$ (24.4)	$ (22.1)	$ (22.5)	$ (22.7)	(107.6)	(91.7)	(100.5)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income									1.4	11.2	8.5
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									52.6	37.9	51.8
Net Impairment Losses Recognized in Earnings									(27.2)	(12.8)	(13.9)
Total Before Income Taxes									25.4	25.1	37.9
Income Tax Benefit (Expense)									(8.9)	(8.8)	(13.2)
Net Income									16.5	16.3	24.7
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)									8.0	2.8	8.8
Net Income									(15.1)	(5.1)	(16.2)
Interest and Other Expenses									$ (23.1)	$ (7.9)	$ (25.0)