Other Comprehensive Income and Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains on Sales of Investments	$ 10.5	$ 6.8
Net Impairment Losses Recognized in Earnings	(5.0)	(9.3)
Total Before Income Taxes	(3.5)	(6.5)
Income Tax Benefit (Expense)	3.1	4.3
Net Loss	(0.3)	(2.1)
Interest and Other Expenses	(19.5)	(22.3)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Loss	3.4	(3.2)
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	10.1	6.8
Net Impairment Losses Recognized in Earnings	(5.0)	(9.3)
Total Before Income Taxes	5.1	(2.5)
Income Tax Benefit (Expense)	(1.8)	0.9
Net Loss	3.3	(1.6)
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 (Expense)	0.0	1.0
Net Loss	0.1	(1.6)
Interest and Other Expenses	$ 0.1	$ (2.6)