Property and Casualty Insurance Reserves - Reserve Activity (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance and Indemnification at Beginning of Year	$ 1,874.9
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Prior Years	(34.6)	$ 1.6
Paid Losses and LAE Related to:
Property and Casualty Insurance Reserves - Gross of Reinsurance at End of Period	1,911.9
Property, Liability and Casualty Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance and Indemnification at Beginning of Year	1,874.9	1,016.8
Less Reinsurance and Indemnification 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	0.0
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Prior Years	(34.6)	1.6
Total Incurred Losses and LAE	1,384.8	743.9
Paid Losses and LAE Related to:
Paid Losses and LAE Related to Prior Years	698.5	363.3
Total Paid Losses and LAE	1,335.1	698.4
Property and Casualty Insurance Reserves - Net of Reinsurance at End of Period	1,826.3	1,009.2
Plus Reinsurance Recoverables at End of Period	85.6	50.5
Property and Casualty Insurance Reserves - Gross of Reinsurance at End of Period	1,911.9	1,059.7
Property, Liability and Casualty Insurance Product Line | Continuing Operations
Incurred Losses and LAE Related to:
Incurred Losses and LAE Related to Current Year	1,419.4	742.3
Incurred Losses and LAE Related to Prior Years	(34.6)	2.0
Paid Losses and LAE Related to:
Paid Losses and LAE Related to Current Year	636.6	335.1
Paid Losses and LAE Related to Prior Years	696.9	361.6
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	(0.4)
Paid Losses and LAE Related to:
Paid Losses and LAE Related to Prior Years	$ 1.6	$ 1.7