Investments - Amortized Cost and Fair Value of Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Cost or Amortized Cost
Due in one year or less, cost or amortized cost	$ 182.5
Due after one year through five years, cost or amortized cost	1,697.8
Due after five years through ten years, cost or amortized cost	2,241.6
Due after ten years, cost or amortized cost	1,094.4
Total, cost or amortized cost	5,216.3
Fixed maturity securities, cost or amortized cost	6,863.6	$ 6,903.9
Fair Value
Due in one year or less, fair value	181.6
Due after one year through five years, fair value	1,614.2
Due after five years through ten years, fair value	1,973.5
Due after ten years, fair value	872.9
Total, fair value	4,642.2
Fixed maturity securities, fair value	6,137.9	7,215.3
Commercial mortgage-backed
Cost or Amortized Cost
Cost or amortized cost	461.7
Fair Value
Fair value	411.2
Residential mortgage-backed
Cost or Amortized Cost
Cost or amortized cost	515.5
Fair Value
Fair value	458.3
Asset-backed
Cost or Amortized Cost
Cost or amortized cost	670.1
Fixed maturity securities, cost or amortized cost	670.1	411.1
Fair Value
Fair value	626.2
Fixed maturity securities, fair value	$ 626.2	$ 423.0

Available For Sale Securities Debt Maturities Contractual Maturity Fair Value Total

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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