Property and Casualty Insurance Reserves (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Property and Casulty Insurance Reserve - Gross of Reinsurance at Beginning of Year	$ 931.4	$ 862.8
Property and Casualty Insurance Reserves - Net of Reinsurance and Indemnification at Beginning of Year	881.2	810.8
Incurred Losses and LAE Related to Prior Years	19.7	(21.0)
Total Incurred Losses and LAE	1,091.7	1,010.1
Paid Losses and LAE Related to Prior Years	446.6	366.1
Total Paid Losses and LAE	1,047.3	949.3
Property and Casualty Insurance Reserves - Net of Reinsurance and Indemnification at End of Period	925.6	871.6
Property and Casualty Insurance Reserves - Gross of Reinsurance and Indemnification at End of Period	968.5	920.7
Continuing Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Current Year	1,072.0	1,031.1
Incurred Losses and LAE Related to Prior Years	19.7	(17.7)
Paid Losses and LAE Related to Current Year	600.7	583.2
Paid Losses and LAE Related to Prior Years	443.6	360.8
Discontinued Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	0.0	(3.3)
Paid Losses and LAE Related to Prior Years	3.0	5.3
Personal Automobile [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	18.1	7.3
Homeowners [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(0.1)	(18.1)
Other Personal Lines [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(0.3)	(6.9)
Property and Casualty, Personal Insurance Product Line [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	17.7	(17.7)
Property and Casualty, Commercial Insurance Product Line [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	2.0	(3.3)
Property and Casualty, Commercial Insurance Product Line [Member] | Continuing Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years		0.0
Property and Casualty, Commercial Insurance Product Line [Member] | Discontinued Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years		(3.3)
Catastrophe [Member] | Homeowners [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(3.2)	(14.3)
Property and Casualty Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less Reinsurance and Indemnification Recoverables at Beginning of Year	50.2	52.0
Plus Reinsurance and Indemnification Recoverables at End of Period	$ 42.9	$ 49.1