Investment Securities - Cost and Amortized Cost Maturity Schedule (Details) $ in Millions	Jun. 30, 2022 USD ($)
Cost or Amortized Cost
Total fixed maturity investments	$ 1,987.6
Carrying Value
Total fixed maturity investments	1,866.7
Fixed Maturities and Convertible Fixed Maturities Excluding Mortgage Backed Securities
Cost or Amortized Cost
Due in one year or less	205.1
Due after one year through five years	892.5
Due after five years through ten years	361.1
Due after ten years	109.6
Carrying Value
Due in one year or less	202.2
Due after one year through five years	843.7
Due after five years through ten years	330.0
Due after ten years	104.4
Mortgage and asset-backed securities
Cost or Amortized Cost
Mortgage and asset-backed securities and collateralized loan obligations	419.3
Carrying Value
Mortgage and asset-backed securities and collateralized loan obligations	$ 386.4

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