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Investment Securities - Other Long-Term Investments (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | $ 2,958.5 | $ 2,150.2
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 689.7 | 547.8
Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,291.4 | 1,014.0
Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 977.4 | 588.4
Bamboo SPV |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 250.0 |
Bamboo SPV | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 |
Bamboo SPV | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 |
Bamboo SPV | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 250.0 |
PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 170.0 | 150.0
PassportCard/DavidShield | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
PassportCard/DavidShield | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
PassportCard/DavidShield | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 170.0 | 150.0
BroadStreet SPV |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 160.0 |
BroadStreet SPV | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 |
BroadStreet SPV | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 |
BroadStreet SPV | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 160.0 |
Elementum |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 35.0 | 35.0
Elementum | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Elementum | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Elementum | Other Operations |  |
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 | 73.7 | 63.6
Other unconsolidated entities | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other unconsolidated entities | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other unconsolidated entities | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 73.7 | 63.6
Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 395.2 | 360.6
Private equity funds and hedge funds | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 167.1 | 104.1
Private equity funds and hedge funds | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Private equity funds and hedge funds | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 228.1 | 256.5
Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 308.5 | 264.7
Bank loan fund | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 308.5 | 264.7
Bank loan fund | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Bank loan fund | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 180.4 | 149.9
Lloyd’s trust deposits | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 180.4 | 149.9
Lloyd’s trust deposits | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Lloyd’s trust deposits | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 50.1 | 74.0
ILS funds | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
ILS funds | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
ILS funds | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 50.1 | 74.0
Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 16.9 | 14.9
Private debt instruments | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Private debt instruments | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 6.4 | 5.6
Private debt instruments | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 10.5 | 9.3
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 33.7 | 29.1
Other | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 33.7 | 29.1
Other | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Other | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Kudu’s Participation Contracts | Kudu |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,285.0 | 1,008.4
Kudu’s Participation Contracts | Kudu | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Kudu’s Participation Contracts | Kudu | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,285.0 | 1,008.4
Kudu’s Participation Contracts | Kudu | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Total unconsolidated entities | Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,973.7 | 1,257.0
Total unconsolidated entities | Total unconsolidated entities | Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 0.0 | 0.0
Total unconsolidated entities | Total unconsolidated entities | Operating Segments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | 1,285.0 | 1,008.4
Total unconsolidated entities | Total unconsolidated entities | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other long-term investments | $ 688.7 | $ 248.6

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