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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains (Losses) on Sales of Investments	$ 9.1	$ 11.6	$ 5.6	$ 6.8	$ 9.4	$ 5.3	$ 34.0	$ 3.4	$ 33.1	$ 52.1	$ 39.1
Net Impairment Losses Recognized in Earnings	(8.7)	(8.3)	(6.4)	(9.3)	(14.7)	(3.3)	(2.2)	(7.0)	(32.7)	(27.2)	(15.2)
Interest and Other Expenses	(25.3)	(22.0)	(20.7)	(22.3)	(25.6)	(25.7)	(26.6)	(29.7)	(90.3)	(107.6)	(91.7)
Income Tax Benefit (Expense)	(11.5)	14.9	1.5	4.3	2.9	(11.8)	(6.9)	(4.3)	9.2	(20.1)	(47.6)
Net Income	$ 31.2	$ (16.3)	$ 4.0	$ (2.1)	$ 4.6	$ 37.9	$ 29.7	$ 13.5	16.8	85.7	114.5
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income									(4.1)	1.4	11.2
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									32.0	52.6	37.9
Net Impairment Losses Recognized in Earnings									(32.2)	(27.2)	(12.8)
Total Before Income Taxes									(0.2)	25.4	25.1
Income Tax Benefit (Expense)									0.1	(8.9)	(8.8)
Net Income									(0.1)	16.5	16.3
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and Other Expenses									(6.3)	(23.1)	(7.9)
Income Tax Benefit (Expense)									2.3	8.0	2.8
Net Income									$ (4.0)	$ (15.1)	$ (5.1)