Investments - Contractual Maturities of Bonds (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Cost or Amortized Cost
Due in one year or less	$ 251.4
Due after one year through five years	470.8
Due after five years through ten years	0.0
Due after ten years	0.0
Cost or Amortized Cost	722.2	$ 696.8
Fair Value
Due in one year or less	246.1
Due after one year through five years	447.0
Due after five years through ten years	0.0
Due after ten years	0.0
Fair Value	$ 693.1	$ 691.4