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Investment Securities - Other Long-Term Investments (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | $ 2,071.1 | $ 1,998.2
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 | 56.6 | 48.1
Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 349.0 | 312.9
Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 258.9 | 194.4
Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 172.7 | 158.0
ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 71.2 | 160.5
Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 15.8 | 15.8
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 31.3 | 33.0
Kudu’s Participation Contracts | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 930.6 | 890.5
Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,172.2 | 1,123.6
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 544.8 | 440.9
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 | 81.9 | 55.5
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 | 258.9 | 194.4
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 | 172.7 | 158.0
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 | 31.3 | 33.0
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 | 936.8 | 896.3
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 | 6.2 | 5.8
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 | 930.6 | 890.5
Operating Segments | Asset Management (Kudu) | Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 930.6 | 890.5
Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 589.5 | 661.0
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 | 56.6 | 48.1
Other Operations | Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 267.1 | 257.4
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 | 71.2 | 160.5
Other Operations | Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 9.6 | 10.0
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 | $ 241.6 | $ 233.1

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