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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Realized Gains on Sales of Investments	$ 3.5	$ 2.3	$ 10.1	$ 29.2
Net Impairment Losses Recognized in Earnings	(4.1)	(1.0)	(4.9)	(2.9)
Total Before Income Taxes	11.2	46.4	63.1	131.0
Interest and Other Expenses	(22.5)	(25.2)	(45.2)	(49.0)
Income Tax Expense	(1.9)	(13.9)	(18.6)	(39.9)
Total Reclassification from AOCI to Net Income	9.3	34.0	44.4	92.4
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassification from AOCI to Net Income	(1.7)	(3.6)	(0.1)	8.6
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	2.2	8.6	28.2
Net Impairment Losses Recognized in Earnings	(4.1)	(1.0)	(4.9)	(2.9)
Total Before Income Taxes	(0.7)	1.2	3.7	25.3
Income Tax Expense	0.2	(0.4)	(1.3)	(8.8)
Total Reclassification from AOCI to Net Income	(0.5)	0.8	2.4	16.5
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	(1.9)	(6.7)	(3.9)	(12.1)
Income Tax Expense	0.7	2.3	1.4	4.2
Total Reclassification from AOCI to Net Income	$ (1.2)	$ (4.4)	$ (2.5)	$ (7.9)