Investments - Contractual Maturities of Bonds (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Cost or Amortized Cost
Due in one year or less	$ 271.1
Due after one year through five years	351.3
Due after five years through ten years	0.2
Due after ten years	0.0
Cost or Amortized Cost	622.6	$ 607.1
Fair Value
Due in one year or less	271.5
Due after one year through five years	352.8
Due after five years through ten years	0.2
Due after ten years	0.0
Fair Value	$ 624.5	$ 607.4