Catastrophe Reinsurance - Catastrophe Losses and LAE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	$ 71.3	$ 87.6	$ 75.2
Non-Core Operations | Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	48.6	52.4	48.3
Specialty Property & Casualty Insurance | Operating Segments
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	2,541.7	3,141.9	3,578.2
Specialty Property & Casualty Insurance | Operating Segments | Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	20.6	32.2	23.6
Life Insurance | Operating Segments | Catastrophe Reinsurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	$ 2.1	$ 3.0	$ 3.3