Property and Casualty Insurance Reserves - Reserve Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Incurred Losses and LAE related to:
Incurred Losses and LAE Related to Prior Years	$ (1.1)	$ 8.8
Property, Liability and Casualty Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross of Reinsurance at Beginning of Year	2,611.9	2,680.5
Less: Reinsurance Recoverables at Beginning of Year	24.3	27.8
Property and Casualty Insurance Reserves, Net of Reinsurance at Beginning of Year	2,587.6	2,652.7
Incurred Losses and LAE related to:
Incurred Losses and LAE Related to Current Year	698.7	686.1
Total Incurred Losses and LAE	697.6	694.9
Paid Losses and LAE related to:
Paid Losses and LAE Related to Current Year	192.5	213.9
Paid Losses and LAE Related to Prior Years	480.4	562.9
Total Paid Losses and LAE	672.9	776.8
Property and Casualty Insurance Reserves, Net of Reinsurance at End of Period	2,612.3	2,570.8
Plus: Reinsurance Recoverables at End of Period	25.3	26.4
Property and Casualty Insurance Reserves, Gross of Reinsurance at End of Period	$ 2,637.6	$ 2,597.2