Property and Casualty Insurance Reserves - Reserve Activity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Incurred Losses and LAE related to:
Incurred Losses and LAE Related to Prior Years			$ 14.4	$ 17.0
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			1,440.4	1,359.2
Total Incurred Losses and LAE			1,454.8	1,376.2
Paid Losses and LAE related to:
Paid Losses and LAE Related to Current Year			535.1	555.1
Paid Losses and LAE Related to Prior Years	$ 866.8	$ 932.9
Total Paid Losses and LAE			1,401.9	1,488.0
Property and Casualty Insurance Reserves, Net of Reinsurance at End of Period	2,640.5	2,540.9	2,640.5	2,540.9
Plus: Reinsurance Recoverables at End of Period	24.2	26.3	24.2	26.3
Property and Casualty Insurance Reserves, Gross of Reinsurance at End of Period	$ 2,664.7	$ 2,567.2	$ 2,664.7	$ 2,567.2