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Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Total mortgage and asset-backed securities and collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | $ 740.0 | $ 610.6
Total mortgage and asset-backed securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 393.0 | 373.9
Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 354.0 | 370.0
Mortgage-backed securities: | Total non-agency |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.4
Mortgage-backed securities: | Total agency |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 354.0 | 369.6
Mortgage-backed securities: | FNMA |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 192.1 | 198.3
Mortgage-backed securities: | FHLMC |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 141.3 | 147.1
Mortgage-backed securities: | GNMA |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 20.6 | 24.2
Mortgage-backed securities: | Non-agency: Commercial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.4
Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 39.0 | 3.9
Other asset-backed securities: | Vehicle receivables |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 21.9 | 1.7
Other asset-backed securities: | Credit card receivables |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 14.0 | 0.2
Other asset-backed securities: | Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 3.1 | 2.0
Collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 347.0 | 236.7
Level 2 | Total mortgage and asset-backed securities and collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 740.0 | 610.6
Level 2 | Total mortgage and asset-backed securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 393.0 | 373.9
Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 354.0 | 370.0
Level 2 | Mortgage-backed securities: | Total non-agency |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.4
Level 2 | Mortgage-backed securities: | Total agency |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 354.0 | 369.6
Level 2 | Mortgage-backed securities: | FNMA |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 192.1 | 198.3
Level 2 | Mortgage-backed securities: | FHLMC |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 141.3 | 147.1
Level 2 | Mortgage-backed securities: | GNMA |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 20.6 | 24.2
Level 2 | Mortgage-backed securities: | Non-agency: Commercial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.4
Level 2 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 39.0 | 3.9
Level 2 | Other asset-backed securities: | Vehicle receivables |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 21.9 | 1.7
Level 2 | Other asset-backed securities: | Credit card receivables |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 14.0 | 0.2
Level 2 | Other asset-backed securities: | Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 3.1 | 2.0
Level 2 | Collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 347.0 | 236.7
Level 3 | Total mortgage and asset-backed securities and collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Total mortgage and asset-backed securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: | Total non-agency |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: | Total agency |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: | FNMA |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: | FHLMC |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: | GNMA |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Mortgage-backed securities: | Non-agency: Commercial |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Other asset-backed securities: | Vehicle receivables |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Other asset-backed securities: | Credit card receivables |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Other asset-backed securities: | Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | 0.0 | 0.0
Level 3 | Collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed maturity investments, at fair value | $ 0.0 | $ 0.0

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