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, 2014	Mar. 31, 2013
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains on Sales of Investments	$ 6.6	$ 26.9
Net Impairment Losses Recognized in Earnings	(0.8)	(1.9)
Total Before Income Taxes	51.9	84.6
Interest and Other Expenses	(22.7)	(23.8)
Income Tax Expense	(16.7)	(26.0)
Total Reclassification from AOCI to Net Income	35.1	58.4
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassification from AOCI to Net Income	1.6	12.2
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	5.2	26.0
Net Impairment Losses Recognized in Earnings	(0.8)	(1.9)
Total Before Income Taxes	4.4	24.1
Income Tax Expense	(1.5)	(8.4)
Total Reclassification from AOCI to Net Income	2.9	15.7
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	(2.0)	(5.4)
Income Tax Expense	0.7	1.9
Total Reclassification from AOCI to Net Income	$ (1.3)	$ (3.5)