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Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Total mortgage and asset-backed securities and collateralized loan obligations |  |
Investment securities |  |
Fixed maturity investments, at fair value | $ 598.5 | $ 437.1
Mortgage and asset-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 389.4 | 254.2
Total mortgage-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 366.4 | 231.9
Total mortgage-backed securities | Total non-agency |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.2 | 0.3
Total mortgage-backed securities | Total agency |  |
Investment securities |  |
Fixed maturity investments, at fair value | 366.2 | 231.6
Total mortgage-backed securities | FNMA |  |
Investment securities |  |
Fixed maturity investments, at fair value | 198.8 | 124.5
Total mortgage-backed securities | FHLMC |  |
Investment securities |  |
Fixed maturity investments, at fair value | 137.2 | 78.8
Total mortgage-backed securities | GNMA |  |
Investment securities |  |
Fixed maturity investments, at fair value | 30.2 | 28.3
Total mortgage-backed securities | Non-agency: Residential |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.2 | 0.3
Total other asset-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 23.0 | 22.3
Total other asset-backed securities | Credit card receivables |  |
Investment securities |  |
Fixed maturity investments, at fair value | 3.3 | 11.9
Total other asset-backed securities | Vehicle receivables |  |
Investment securities |  |
Fixed maturity investments, at fair value | 17.2 | 10.4
Total other asset-backed securities | Other |  |
Investment securities |  |
Fixed maturity investments, at fair value | 2.5 | 0.0
Collateralized loan obligations |  |
Investment securities |  |
Fixed maturity investments, at fair value | 209.1 | 182.9
Level 2 | Total mortgage and asset-backed securities and collateralized loan obligations |  |
Investment securities |  |
Fixed maturity investments, at fair value | 598.5 | 437.1
Level 2 | Mortgage and asset-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 389.4 | 254.2
Level 2 | Total mortgage-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 366.4 | 231.9
Level 2 | Total mortgage-backed securities | Total non-agency |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.2 | 0.3
Level 2 | Total mortgage-backed securities | Total agency |  |
Investment securities |  |
Fixed maturity investments, at fair value | 366.2 | 231.6
Level 2 | Total mortgage-backed securities | FNMA |  |
Investment securities |  |
Fixed maturity investments, at fair value | 198.8 | 124.5
Level 2 | Total mortgage-backed securities | FHLMC |  |
Investment securities |  |
Fixed maturity investments, at fair value | 137.2 | 78.8
Level 2 | Total mortgage-backed securities | GNMA |  |
Investment securities |  |
Fixed maturity investments, at fair value | 30.2 | 28.3
Level 2 | Total mortgage-backed securities | Non-agency: Residential |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.2 | 0.3
Level 2 | Total other asset-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 23.0 | 22.3
Level 2 | Total other asset-backed securities | Credit card receivables |  |
Investment securities |  |
Fixed maturity investments, at fair value | 3.3 | 11.9
Level 2 | Total other asset-backed securities | Vehicle receivables |  |
Investment securities |  |
Fixed maturity investments, at fair value | 17.2 | 10.4
Level 2 | Total other asset-backed securities | Other |  |
Investment securities |  |
Fixed maturity investments, at fair value | 2.5 | 0.0
Level 2 | Collateralized loan obligations |  |
Investment securities |  |
Fixed maturity investments, at fair value | 209.1 | 182.9
Level 3 | Total mortgage and asset-backed securities and collateralized loan obligations |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage and asset-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities | Total non-agency |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities | Total agency |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities | FNMA |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities | FHLMC |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities | GNMA |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage-backed securities | Non-agency: Residential |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total other asset-backed securities |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total other asset-backed securities | Credit card receivables |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total other asset-backed securities | Vehicle receivables |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total other asset-backed securities | Other |  |
Investment securities |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Collateralized loan obligations |  |
Investment securities |  |
Fixed maturity investments, at fair value | $ 0.0 | $ 0.0

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