XML 68 R58.htm IDEA: XBRL DOCUMENT
v3.23.1

Investment Securities - Other long-term investments (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | $ 1,643.0 | $ 1,488.0
Asset Management (Kudu) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 683.2 | 695.9
PassportCard/DavidShield |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 140.0 | 135.0
Elementum Holdings, L.P. |  |
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
Total unconsolidated entities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 940.7 | 898.1
Private equity funds and hedge funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 218.5 | 197.8
Bank loan fund |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 179.5 | 174.8
Lloyd’s trust deposits |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 148.7 | 137.4
ILS funds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 123.6 | 49.3
Private debt instruments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | 10.1 | 9.6
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total other long-term investments | $ 21.9 | $ 21.0

X
- Definition Amount of long-term investments classified as other. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(f)) -URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + 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: | us-gaap_FinancialInstrumentAxis=wtm_KuduInvestmentManagementLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

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

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=wtm_HedgeFundsAndPrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=wtm_ForeignRegulatoryDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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