Property and Casualty Insurance Reserves - Reserve Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance at Beginning of Year	$ 6,102.9
Less: Reinsurance Recoverables at Beginning of Year	86.5
Incurred Losses and LAE related to:
Prior Years	22.6		$ (14.6)
Paid Losses and LAE related to:
Plus: Reinsurance Recoverables at End of Year	78.7	$ 86.5
Property and Casualty Insurance Reserves, Gross of Reinsurance at End of Year	5,811.6	6,102.9
Property and Liability Insurance
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance at Beginning of Year	2,680.5	2,756.9	2,772.7
Less: Reinsurance Recoverables at Beginning of Year	27.8	39.6	41.9
Property and Casualty Insurance Reserves, Net of Reinsurance at Beginning of Year	2,652.7	2,717.3	2,730.8
Incurred Losses and LAE related to:
Current Year	2,745.9	3,429.9	4,103.3
Prior Years	29.8	159.8	(14.6)
Total Incurred Losses and LAE	2,775.7	3,589.7	4,088.7
Paid Losses and LAE related to:
Paid Losses and LAE Related to Current Year	1,383.0	1,965.3	2,460.5
Paid Losses and LAE Related to Prior Years	1,457.8	1,689.0	1,641.7
Total Paid Losses and LAE	2,840.8	3,654.3	4,102.2
Property and Casualty Insurance Reserves, Net of Reinsurance at End of Year	2,587.6	2,652.7	2,717.3
Plus: Reinsurance Recoverables at End of Year	24.3	27.8	39.6
Property and Casualty Insurance Reserves, Gross of Reinsurance at End of Year	$ 2,611.9	$ 2,680.5	$ 2,756.9