Investment Securities - Cost and Amortized Cost Maturity Schedule (Details) $ in Millions	Sep. 30, 2022 USD ($)
Cost or Amortized Cost
Total fixed maturity investments	$ 2,034.0
Carrying Value
Total fixed maturity investments	1,854.3
Fixed Maturities and Convertible Fixed Maturities Excluding Mortgage Backed Securities
Cost or Amortized Cost
Due in one year or less	207.5
Due after one year through five years	917.9
Due after five years through ten years	354.8
Due after ten years	105.8
Carrying Value
Due in one year or less	203.8
Due after one year through five years	849.4
Due after five years through ten years	309.3
Due after ten years	93.8
Mortgage and asset-backed securities
Cost or Amortized Cost
Mortgage and asset-backed securities and collateralized loan obligations	448.0
Carrying Value
Mortgage and asset-backed securities and collateralized loan obligations	$ 398.0

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