Business Segments - Segment Operating Profit (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Income (Loss)									$ 118.9	$ 3.1	$ 84.5
Net Realized Gains on Sales of Investments	$ 11.5	$ 8.1	$ 26.4	$ 10.5	$ 9.1	$ 11.6	$ 5.6	$ 6.8	56.5	33.1	52.1
Net Impairment Losses Recognized in Earnings	(3.8)	(2.9)	(2.6)	(5.0)	(8.7)	(8.3)	(6.4)	(9.3)	(14.3)	(32.7)	(27.2)
Loss from Early Extinguishment of Debt									0.0	0.0	9.1
Income (Loss) from Continuing Operations before Income Taxes	$ 44.2	$ 68.3	$ 52.1	$ (3.5)	$ 40.6	$ (33.2)	$ 2.6	$ (6.5)	161.1	3.5	100.3
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)									137.1	28.5	133.4
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)									(1.4)	(17.2)	23.7
Operating Segments [Member] | Life and Health Insurance [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)									138.5	45.7	109.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)									(18.2)	(25.4)	(48.9)
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Net Realized Gains on Sales of Investments									56.5	33.1	52.1
Net Impairment Losses Recognized in Earnings									(14.3)	(32.7)	(27.2)
Loss from Early Extinguishment of Debt									$ 0.0	$ 0.0	$ (9.1)