Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains on Sales of Investments	$ 3.4	$ 6.6
Net Impairment Losses Recognized in Earnings	(7.0)	(0.8)
Total Before Income Taxes	17.8	51.9
Interest and Other Expenses	(29.7)	(22.7)
Income Tax Benefit (Expense)	(4.3)	(16.7)
Total Reclassification from AOCI to Net Income	13.5	35.1
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassification from AOCI to Net Income	(6.0)	1.6
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	3.4	5.2
Net Impairment Losses Recognized in Earnings	(7.0)	(0.8)
Total Before Income Taxes	(3.6)	4.4
Income Tax Benefit (Expense)	1.3	(1.5)
Total Reclassification from AOCI to Net Income	(2.3)	2.9
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest and Other Expenses	(5.4)	(2.0)
Income Tax Benefit (Expense)	1.7	0.7
Total Reclassification from AOCI to Net Income	$ (3.7)	$ (1.3)