XML 86 R69.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Investment Securities - Other Long-Term Investments (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Investment securities |  |
Other long-term investments | $ 1,998.2 | $ 1,488.0
Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 440.9 | 373.6
Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 896.3 | 695.9
Other Operations |  |
Investment securities |  |
Other long-term investments | 661.0 | 418.5
PassportCard/DavidShield |  |
Investment securities |  |
Other long-term investments | 150.0 | 135.0
PassportCard/DavidShield | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
PassportCard/DavidShield | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
PassportCard/DavidShield | Other Operations |  |
Investment securities |  |
Other long-term investments | 150.0 | 135.0
Elementum Holdings, L.P. |  |
Investment securities |  |
Other long-term investments | 35.0 | 30.0
Elementum Holdings, L.P. | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Elementum Holdings, L.P. | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Elementum Holdings, L.P. | Other Operations |  |
Investment securities |  |
Other long-term investments | 35.0 | 30.0
Other unconsolidated entities |  |
Investment securities |  |
Other long-term investments | 48.1 | 37.2
Other unconsolidated entities | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Other unconsolidated entities | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Other unconsolidated entities | Other Operations |  |
Investment securities |  |
Other long-term investments | 48.1 | 37.2
Private equity funds and hedge funds |  |
Investment securities |  |
Other long-term investments | 312.9 | 197.8
Private equity funds and hedge funds | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 55.5 | 40.4
Private equity funds and hedge funds | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Private equity funds and hedge funds | Other Operations |  |
Investment securities |  |
Other long-term investments | 257.4 | 157.4
Bank loan fund |  |
Investment securities |  |
Other long-term investments | 194.4 | 174.8
Bank loan fund | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 194.4 | 174.8
Bank loan fund | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Bank loan fund | Other Operations |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
ILS funds |  |
Investment securities |  |
Other long-term investments | 160.5 | 49.3
ILS funds | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
ILS funds | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
ILS funds | Other Operations |  |
Investment securities |  |
Other long-term investments | 160.5 | 49.3
Lloyd’s trust deposits |  |
Investment securities |  |
Other long-term investments | 158.0 | 137.4
Lloyd’s trust deposits | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 158.0 | 137.4
Lloyd’s trust deposits | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Lloyd’s trust deposits | Other Operations |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Private debt instruments |  |
Investment securities |  |
Other long-term investments | 10.0 | 9.6
Private debt instruments | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Private debt instruments | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Private debt instruments | Other Operations |  |
Investment securities |  |
Other long-term investments | 10.0 | 9.6
Other |  |
Investment securities |  |
Other long-term investments | 38.8 | 21.0
Other | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 33.0 | 21.0
Other | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 5.8 | 0.0
Other | Other Operations |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Kudu’s Participation Contracts | Kudu |  |
Investment securities |  |
Other long-term investments | 890.5 | 695.9
Kudu’s Participation Contracts | Kudu | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Kudu’s Participation Contracts | Kudu | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 890.5 | 695.9
Kudu’s Participation Contracts | Kudu | Other Operations |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Investments, Excluding MediaAlpha | Total unconsolidated entities |  |
Investment securities |  |
Other long-term investments | 1,123.6 | 898.1
Investments, Excluding MediaAlpha | Total unconsolidated entities | Operating Segments | Ark |  |
Investment securities |  |
Other long-term investments | 0.0 | 0.0
Investments, Excluding MediaAlpha | Total unconsolidated entities | Operating Segments | Kudu |  |
Investment securities |  |
Other long-term investments | 890.5 | 695.9
Investments, Excluding MediaAlpha | Total unconsolidated entities | Other Operations |  |
Investment securities |  |
Other long-term investments | $ 233.1 | $ 202.2

X
- 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
Name: | us-gaap_OtherLongTermInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wtm_ArkInsuranceHoldingsLimitedWMOutriggerReSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wtm_KuduInvestmentManagementLLCSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ConsolidationItemsAxis=us-gaap_CorporateNonSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_DavidShieldPassportCardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_ElementumHoldingsL.P.Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_OtherUnconsolidatedPrivateEquityInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_PrivateEquityFundsAndHedgeFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_BankLoanFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_InsuranceLinkedSecuritiesFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_TrustDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_PrivateDebtInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_OtherFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wtm_KuduParticipationContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_KuduInvestmentManagementLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=wtm_InvestmentsExcludingMediaAlphaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=wtm_TotalUnconsolidatedEntitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |