Property and Casualty Insurance Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Property and Casulty Insurance Reserve - Gross of Reinsurance at Beginning of Year	$ 1,016.8	$ 931.4
Property and Casualty Insurance Reserves - Net of Reinsurance and Indemnification at Beginning of Year	963.7	881.2
Incurred Losses and LAE Related to Prior Years	(1.3)	10.9
Total Incurred Losses and LAE	338.0	383.9
Paid Losses and LAE Related to Prior Years	222.9	212.4
Total Paid Losses and LAE	348.2	333.0
Property and Casualty Insurance Reserves - Net of Reinsurance and Indemnification at End of Period	953.5	932.1
Property and Casualty Insurance Reserves - Gross of Reinsurance and Indemnification at End of Period	1,005.1	984.4
Continuing Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Current Year	339.3	373.0
Incurred Losses and LAE Related to Prior Years	(1.0)	11.1
Paid Losses and LAE Related to Current Year	125.3	120.6
Paid Losses and LAE Related to Prior Years	222.2	211.6
Discontinued Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(0.3)	(0.2)
Paid Losses and LAE Related to Prior Years	0.7	0.8
Personal Automobile [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	0.5	9.9
Homeowners [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	0.5	0.1
Other Personal Lines [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(1.2)	(0.7)
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	(0.3)	9.3
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	(1.0)	1.6
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		1.8
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		(0.2)
Catastrophe [Member] | Homeowners [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(5.1)	(0.6)
Property and Casualty Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less Reinsurance and Indemnification Recoverables at Beginning of Year	53.1	50.2
Plus Reinsurance and Indemnification Recoverables at End of Period	$ 51.6	$ 52.3