Property and Casualty Insurance Reserves - Reserve Activity (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance at Beginning of Year	$ 1,874.9
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Prior Years	(55.8)	$ (1.7)
Paid Losses and LAE Related to:
Property and Casualty Insurance Reserves - Gross of Reinsurance at End of Period	1,941.6
Property, Liability and Casualty Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance at Beginning of Year	1,874.9	1,016.8
Less Reinsurance Recoverables at Beginning of Year	101.9	53.1
Property and Casualty Insurance Reserves - Net of Reinsurance at Beginning of Year	1,773.0	963.7
Property and Casualty Insurance Reserves Acquired, Net of Reinsurance	3.6	682.9
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Prior Years	(55.8)	(1.7)
Total Incurred Losses and LAE	2,084.3	1,411.0
Paid Losses and LAE Related to:
Paid Losses and LAE Related to Prior Years	853.1	535.3
Total Paid Losses and LAE	1,981.9	1,306.2
Property and Casualty Insurance Reserves - Net of Reinsurance at End of Period	1,879.0	1,751.4
Plus Reinsurance Recoverables at End of Period	62.6	67.7
Property and Casualty Insurance Reserves - Gross of Reinsurance at End of Period	1,941.6	1,819.1
Property, Liability and Casualty Insurance Product Line | Continuing Operations
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Current Year	2,140.1	1,412.7
Incurred Losses and LAE Related to Prior Years	(55.8)	(1.2)
Paid Losses and LAE Related to:
Paid Losses and LAE Related to Current Year	1,128.8	770.9
Paid Losses and LAE Related to Prior Years	850.7	533.1
Property, Liability and Casualty Insurance Product Line | Discontinued Operations
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Prior Years	0.0	(0.5)
Paid Losses and LAE Related to:
Paid Losses and LAE Related to Prior Years	$ 2.4	$ 2.2