Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains on Sales of Investments	$ 6.8	$ 3.4
Net Impairment Losses Recognized in Earnings	(9.3)	(7.0)
Total Before Income Taxes	(6.5)	17.8
Income Tax Benefit	4.3	(4.3)
Interest and Other Expenses	(22.3)	(29.7)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassification from AOCI to Net Income	(3.2)	(6.0)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains on Sales of Investments	6.8	3.4
Net Impairment Losses Recognized in Earnings	(9.3)	(7.0)
Total Before Income Taxes	(2.5)	(3.6)
Income Tax Benefit	0.9	1.3
Total Reclassification from AOCI to Net Income	(1.6)	(2.3)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Benefit	1.0	1.7
Interest and Other Expenses	(2.6)	(5.4)
Total Reclassification from AOCI to Net Income	$ (1.6)	$ (3.7)