Catastrophe Reinsurance - Catastrophe Losses and LAE (Details) - Catastrophe - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	$ 75.2	$ 102.4	$ 106.9
Specialty Property & Casualty Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	23.6	16.0	12.5
Preferred Property & Casualty Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	48.3	73.5	81.5
Life & Health Insurance
Liability for Catastrophe Claims [Line Items]
Catastrophe Losses and LAE	$ 3.3	$ 12.9	$ 12.9