Investments - Contractual Maturities of Bonds (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Cost or Amortized Cost
Due in one year or less	$ 213.0
Due after one year through five years	452.7
Due after five years through ten years	0.0
Due after ten years	0.0
Cost or Amortized Cost	665.7	$ 673.5
Fair Value
Due in one year or less	208.9
Due after one year through five years	439.6
Due after five years through ten years	0.0
Due after ten years	0.0
Fair Value	$ 648.5	$ 650.3