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Investment Securities - Other Long-Term Investments (Details) - USD ($) $ in Millions | Mar. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | $ 2,287.9 | $ 2,150.2
PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 150.0 | 150.0
Elementum |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 35.0 | 35.0
Other unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 64.7 | 63.6
Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 379.2 | 360.6
Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 264.9 | 264.7
Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 155.9 | 149.9
ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 71.3 | 74.0
Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 15.3 | 14.9
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 31.2 | 29.1
Kudu’s Participation Contracts | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,120.4 | 1,008.4
Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,370.1 | 1,257.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 586.8 | 547.8
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Elementum |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Other unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 134.8 | 104.1
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 264.9 | 264.7
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 155.9 | 149.9
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 31.2 | 29.1
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Kudu’s Participation Contracts | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) | Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,126.2 | 1,014.0
Operating Segments | Asset Management (Kudu) | PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Elementum |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Other unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 5.8 | 5.6
Operating Segments | Asset Management (Kudu) | Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Operating Segments | Asset Management (Kudu) | Kudu’s Participation Contracts | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,120.4 | 1,008.4
Operating Segments | Asset Management (Kudu) | Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,120.4 | 1,008.4
Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 574.9 | 588.4
Other Operations | PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 150.0 | 150.0
Other Operations | Elementum |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 35.0 | 35.0
Other Operations | Other unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 64.7 | 63.6
Other Operations | Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 244.4 | 256.5
Other Operations | Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other Operations | Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other Operations | ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 71.3 | 74.0
Other Operations | Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 9.5 | 9.3
Other Operations | Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other Operations | Kudu’s Participation Contracts | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other Operations | Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | $ 249.7 | $ 248.6

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