Investments - Contractual Maturities of Bonds (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Cost or Amortized Cost
Due in one year or less	$ 217.3
Due after one year through five years	481.1
Due after five years through ten years	0.0
Due after ten years	0.0
Cost or Amortized Cost	698.4	$ 696.8
Fair Value
Due in one year or less	213.7
Due after one year through five years	460.4
Due after five years through ten years	0.0
Due after ten years	0.0
Fair Value	$ 674.1	$ 691.4