Business Segments - Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) segments	Sep. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments | segments			2
Earned Premiums	$ 536.7	$ 462.8	$ 1,468.1	$ 1,410.7
Net Investment Income	75.9	72.3	223.2	216.0
Other Income	0.8	0.5	2.3	0.8
Total Revenues	615.4	539.8	1,723.8	1,636.9
Net Realized Gains on Sales of Investments	5.3	8.0	42.7	18.1
Segment Operating Profit (Loss)	47.8	(0.2)	80.8	57.7
Net Impairment Losses Recognized in Earnings	(3.3)	(3.8)	(12.5)	(8.7)
Loss from Early Extinguishment of Debt	0.0	0.0	9.1	0.0
Income from Continuing Operations before Income Taxes	49.8	4.0	101.9	67.1
Segment Net Operating Income (Loss)	36.6	2.1	65.1	43.2
Income from Continuing Operations	38.0	4.8	78.9	49.3
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	(12.6)	(7.7)	(36.2)	(24.1)
Segment Net Operating Income (Loss)	(7.9)	(4.6)	(20.6)	(14.7)
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Other Income	2.5	4.6	12.6	13.0
Net Realized Gains on Sales of Investments	5.3	8.0	42.7	18.1
Net Impairment Losses Recognized in Earnings	(3.3)	(3.8)	(12.5)	(8.7)
Loss from Early Extinguishment of Debt	0.0	0.0	(9.1)	0.0
Net Realized Gains (Losses) on Sales of Investments, Net of Tax	3.5	5.2	27.8	11.8
Net Impairment Losses Recognized in Earnings, Net of Tax	(2.1)	(2.5)	(8.1)	(5.7)
Loss from Early Extinguishment of Debt, Net of Tax	0.0	0.0	(5.9)	0.0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	610.9	531.0	1,681.0	1,614.5
Segment Operating Profit (Loss)	60.4	7.5	117.0	81.8
Segment Net Operating Income (Loss)	44.5	6.7	85.7	57.9
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Earned Premiums	386.1	309.7	1,023.1	949.5
Net Investment Income	18.3	18.5	51.7	55.6
Other Income	0.1	0.1	0.5	0.4
Total Revenues	404.5	328.3	1,075.3	1,005.5
Segment Operating Profit (Loss)	25.0	(23.9)	34.6	(8.9)
Segment Net Operating Income (Loss)	21.0	(13.6)	31.8	(0.4)
Operating Segments [Member] | Life and Health Insurance [Member]
Segment Reporting Information [Line Items]
Earned Premiums	150.6	153.1	445.0	461.2
Net Investment Income	55.1	49.2	159.0	147.4
Other Income	0.7	0.4	1.7	0.4
Total Revenues	206.4	202.7	605.7	609.0
Segment Operating Profit (Loss)	35.4	31.4	82.4	90.7
Segment Net Operating Income (Loss)	$ 23.5	$ 20.3	$ 53.9	$ 58.3