Property and Casualty Insurance Reserves (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Property and Casulty Insurance Reserve - Gross of Reinsurance at Beginning of Year	$ 1,874.9	$ 1,016.8
Property and Casualty Insurance Reserves - Net of Reinsurance at Beginning of Year	1,773.0	963.7
Incurred Losses and LAE Related to Prior Years	(21.4)	(1.3)
Total Incurred Losses and LAE	666.2	338.0
Paid Losses and LAE Related to Prior Years	445.4	222.9
Total Paid Losses and LAE	668.9	348.2
Property and Casualty Insurance Reserves - Net of Reinsurance at End of Period	1,770.3	953.5	$ 963.7
Property and Casualty Insurance Reserves - Gross of Reinsurance at End of Period	1,868.7	1,005.1	1,016.8
Continuing Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Current Year	687.6	339.3
Incurred Losses and LAE Related to Prior Years	(21.4)	(1.0)
Paid Losses and LAE Related to Current Year	223.5	125.3
Paid Losses and LAE Related to Prior Years	444.5	222.2
Discontinued Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	0.0	(0.3)
Paid Losses and LAE Related to Prior Years	0.9	0.7
Specialty Automobile [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(14.3)
Commercial Automobile Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(3.8)
Commercial Automobile Insurance [Member] | Continuing Operations [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years			(0.7)
Other Personal Lines [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(1.8)	(1.2)
Preferred Automobile [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years	(1.3)	0.5
Non-Catastrophe [Member] | Homeowners [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years		5.6
Catastrophe [Member] | Homeowners [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Incurred Losses and LAE Related to Prior Years		(5.1)
Property and Casualty Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less Reinsurance and Indemnification Recoverables at Beginning of Year	101.9	53.1
Plus Reinsurance Recoverables at End of Period	$ 98.4	$ 51.6	$ 53.1