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Investment Securities - Other long-term investments (Details) - USD ($) $ in Millions | Jun. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | $ 1,815.0 | $ 1,488.0
P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 410.7 | 373.6
Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 737.1 | 695.9
Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 667.2 | 418.5
Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 737.1 | 695.9
Asset Management (Kudu) | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Asset Management (Kudu) | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 737.1 | 695.9
Asset Management (Kudu) | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 150.0 | 135.0
PassportCard/DavidShield | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
PassportCard/DavidShield | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
PassportCard/DavidShield | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 150.0 | 135.0
Elementum Holdings, L.P. |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 30.0 | 30.0
Elementum Holdings, L.P. | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Elementum Holdings, L.P. | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Elementum Holdings, L.P. | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 30.0 | 30.0
Other unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 87.5 | 37.2
Other unconsolidated entities | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Other unconsolidated entities | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Other unconsolidated entities | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 87.5 | 37.2
Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 1,004.6 | 898.1
Total unconsolidated entities | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Total unconsolidated entities | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 737.1 | 695.9
Total unconsolidated entities | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 267.5 | 202.2
Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 289.3 | 197.8
Private equity funds and hedge funds | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 52.8 | 40.4
Private equity funds and hedge funds | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Private equity funds and hedge funds | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 236.5 | 157.4
Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 184.3 | 174.8
Bank loan fund | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 184.3 | 174.8
Bank loan fund | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Bank loan fund | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 153.3 | 49.3
ILS funds | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
ILS funds | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
ILS funds | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 153.3 | 49.3
Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 152.3 | 137.4
Lloyd’s trust deposits | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 152.3 | 137.4
Lloyd’s trust deposits | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Lloyd’s trust deposits | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 9.9 | 9.6
Private debt instruments | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Private debt instruments | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Private debt instruments | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 9.9 | 9.6
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 21.3 | 21.0
Other | P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 21.3 | 21.0
Other | Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 0.0 | 0.0
Other | Other Operations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | $ 0.0 | $ 0.0

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- Definition Amount of long-term investments classified as other. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(1)(f)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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