Business Segments - Segment Revenues (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Earned Premiums	$ 451.5	$ 462.8	$ 470.3	$ 477.6	$ 495.6	$ 507.5	$ 512.8	$ 509.9	$ 1,862.2	$ 2,025.8	$ 2,107.1
Net Investment Income	93.1	72.3	72.6	71.1	76.9	82.4	74.6	80.8	309.1	314.7	295.9
Other Income	0.6	0.5	0.2	0.1	0.3	0.1	0.2	0.2	1.4	0.8	0.8
Total Revenues	559.7	539.8	542.5	554.6	586.0	635.7	588.9	615.9	2,196.6	2,426.5	2,462.3
Net Realized Gains on Sales of Investments	21.0	8.0	3.5	6.6	20.8	49.1	2.3	26.9	39.1	99.1	65.4
Net Impairment Losses Recognized in Earnings	(6.5)	(3.8)	(4.1)	(0.8)	(7.6)	(3.4)	(1.0)	(1.9)	(15.2)	(13.9)	(6.9)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues									2,155.0	2,327.3	2,390.1
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Earned Premiums									1,249.5	1,392.9	1,467.2
Net Investment Income									72.7	90.9	77.9
Other Income									0.5	0.5	0.7
Total Revenues									1,322.7	1,484.3	1,545.8
Operating Segments [Member] | Life and Health Insurance [Member]
Segment Reporting Information [Line Items]
Earned Premiums									612.7	632.9	639.9
Net Investment Income									218.7	209.9	204.3
Other Income									0.9	0.2	0.1
Total Revenues									832.3	843.0	844.3
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Other Income									17.7	14.0	13.7
Net Realized Gains on Sales of Investments									39.1	99.1	65.4
Net Impairment Losses Recognized in Earnings									$ (15.2)	$ (13.9)	$ (6.9)