Property and Casualty Insurance Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Beginning Property and Casualty Insurance Reserves: [Abstract]
Gross of Reinsurance and Indemnification at Beginning of Year	$ 931.4	$ 862.8	$ 733.9
Less Reinsurance Recoverables and Indemnification at Beginning of Year	106.4
Property and Casualty Insurance Reserves, Net of Reinsurance and Indemnification at Beginning of Year	881.2	810.8	679.0
Property and Casualty Insurance Reserves Acquired, Net of Reinsurance and Indemnification				$ 0.0	$ 0.0	$ 125.4
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	18.9	(20.7)	(20.1)
Total Incurred Losses and LAE	1,473.0	1,337.9	1,103.2
Paid Losses and LAE related to:
Prior Years - Paid Losses and LAE	522.4	436.5	373.6
Total Paid Losses and LAE	1,390.5	1,267.5	1,096.8
Property and Casualty Insurance Reserves, Net of Reinsurance and Indemnification at End of Year	881.2	810.8	679.0	$ 963.7	$ 881.2	$ 810.8
Plus Reinsurance and Indemnification Recoverables at End of Year	111.6	106.4
Property and Casualty Insurance Reserves, Gross of Reinsurance at End of Year	1,016.8	931.4	862.8
Continuing Operations [Member]
Incurred Losses and LAE related to:
Current Year - Incurred Losses and LAE	1,454.1	1,358.6	1,123.3
Prior Years - Incurred Losses and LAE	20.4	(14.4)	(11.5)
Paid Losses and LAE related to:
Current Year - Paid Losses and LAE	868.1	831.0	723.2
Prior Years - Paid Losses and LAE	518.5	431.9	366.2
Discontinued Operations [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	(1.5)	(6.3)	(8.6)
Paid Losses and LAE related to:
Prior Years - Paid Losses and LAE	3.9	4.6	7.4
Alliance United [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE			7.7
Catastrophe [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	(4.5)	(19.3)	(7.8)
Total Incurred Losses and LAE	180.4	95.8	60.5
Property and Casualty Insurance [Member]
Beginning Property and Casualty Insurance Reserves: [Abstract]
Less Reinsurance Recoverables and Indemnification at Beginning of Year	50.2	52.0	54.9
Paid Losses and LAE related to:
Plus Reinsurance and Indemnification Recoverables at End of Year	53.1	50.2	52.0
Property and Casualty, Personal Insurance Product Line [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	19.5	(16.8)	(13.3)
Property and Casualty, Commercial Insurance Product Line [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	(0.6)	(3.9)	(6.8)
Property and Casualty, Commercial Insurance Product Line [Member] | Continuing Operations [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	0.9	2.4	1.8
Property and Casualty, Commercial Insurance Product Line [Member] | Discontinued Operations [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	(1.5)	(6.3)	(8.6)
Personal Automobile [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	22.2	11.3	(1.8)
Homeowners [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	1.0	(20.0)	(10.8)
Homeowners [Member] | Catastrophe [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	(3.7)	(16.8)
Other Personal Lines [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE	$ (3.7)	$ (8.1)	(0.7)
Property and Casualty, Personal Insurance Product Line, Excluding Alliance United [Member]
Incurred Losses and LAE related to:
Prior Years - Incurred Losses and LAE			$ (21.0)