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SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Summary of investments other than investments in related parties |  |  |
Cost | $ 5,878.3 |  |
Carrying Value | 6,477.6 |  |
Fair Value | 6,477.6 |  |
Dividend and income distributions from equity method eligible investments | 71.4 | $ 67.0 | $ 68.9
Fixed maturity investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 2,569.2 |  |
Carrying Value | 2,511.6 |  |
Fair Value | 2,511.6 |  |
U.S. Government and agency obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 461.8 |  |
Carrying Value | 462.1 |  |
Fair Value | 462.1 |  |
Debt securities issued by corporations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 1,444.5 |  |
Carrying Value | 1,414.2 |  |
Fair Value | 1,414.2 |  |
Municipal obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 3.2 |  |
Carrying Value | 3.2 |  |
Fair Value | 3.2 |  |
Mortgage and asset-backed securities |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 400.2 |  |
Carrying Value | 373.9 |  |
Fair Value | 373.9 |  |
Collateralized loan obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 237.3 |  |
Carrying Value | 236.7 |  |
Fair Value | 236.7 |  |
Foreign government and agency obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 22.2 |  |
Carrying Value | 21.5 |  |
Fair Value | 21.5 |  |
Short-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 964.2 |  |
Carrying Value | 964.2 |  |
Fair Value | 964.2 |  |
Equity Method Investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 1,083.8 |  |
Carrying Value | 1,423.3 |  |
Equity Method Investments | Investment in MediaAlpha |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 59.2 |  |
Carrying Value | 201.6 |  |
Fair Value | 201.6 |  |
Common equity securities - Industrial, Miscellaneous and Other |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 373.7 |  |
Carrying Value | 425.4 |  |
Fair Value | 425.4 |  |
Exchange-traded funds |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 163.3 |  |
Carrying Value | 224.6 |  |
Fair Value | 224.6 |  |
Total common equity securities |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 537.0 |  |
Carrying Value | 650.0 |  |
Fair Value | 650.0 |  |
Other long-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 1,748.7 |  |
Carrying Value | 2,150.2 |  |
Fair Value | $ 2,150.2 |  |

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