Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Details) $ in Millions	Dec. 31, 2024 USD ($)
Amortized Cost
Due in one year or less	$ 262.5
Due after one year through five years	887.4
Due after five years through ten years	173.0
Due after ten years	20.1
Structured securities	689.9
Total	2,032.9
Fair Value
Due in one year or less	263.9
Due after one year through five years	898.7
Due after five years through ten years	179.4
Due after ten years	20.7
Structured securities	706.2
Total	$ 2,068.9