Investments - Contractual Maturities of Bonds (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Cost or Amortized Cost
Due in one year or less	$ 158.9
Due after one year through five years	555.6
Due after five years through ten years	0.0
Due after ten years	0.0
Cost or Amortized Cost	714.5	$ 696.8
Fair Value
Due in one year or less	157.2
Due after one year through five years	537.5
Due after five years through ten years	0.0
Due after ten years	0.0
Fair Value	$ 694.7	$ 691.4