XML 74 R63.htm IDEA: XBRL DOCUMENT
v3.24.1.u1

Loss and Loss Adjustment Expense Reserves - Reserve Activity (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2021 | Dec. 31, 2020
Loss and loss adjustment expenses incurred relating to: |  |  |  |
Net incurred loss and loss adjustment expenses | $ 185.8 | $ 147.8 |  |
Syndicate - Ark Insurance Holdings Limited |  |  |  |
Loss and loss adjustment expenses paid relating to: |  |  |  |
Percent of underwriting capital provided by third parties |  |  | 0.00% | 42.80%
P&C Insurance and Reinsurance (Ark/WM Outrigger) |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Gross beginning balance | 1,605.1 | 1,296.5 |  |
Less: beginning reinsurance recoverable on unpaid losses | (340.8) | (505.0) |  |
Net loss and loss adjustment expense reserves | 1,264.3 | 791.5 |  |
Loss and loss adjustment expenses incurred relating to: |  |  |  |
Current year losses | 180.3 | 139.2 |  |
Prior year losses | (0.3) | 8.6 |  |
Net incurred loss and loss adjustment expenses | 180.0 | 147.8 |  |
Loss and loss adjustment expenses paid relating to: |  |  |  |
Current year losses | (4.0) | (4.0) |  |
Prior year losses | (96.7) | (87.7) |  |
Net paid loss and loss adjustment expenses | (100.7) | (91.7) |  |
Change in TPC providers’ participation | 0.0 | 145.4 |  |
Foreign currency translation and other adjustments to loss and loss adjustment expense reserves | (3.6) | 3.7 |  |
Net ending balance | 1,340.0 | 996.7 |  |
Plus: ending reinsurance recoverable on unpaid losses | (404.5) | (348.9) |  |
Gross ending balance | 1,744.5 | 1,345.6 |  |
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Gross beginning balance | 1,605.1 |  |  |
Loss and loss adjustment expenses incurred relating to: |  |  |  |
Net incurred loss and loss adjustment expenses | 180.0 | 147.8 |  |
Loss and loss adjustment expenses paid relating to: |  |  |  |
Gross ending balance | 1,744.5 |  |  |
P&C Insurance and Reinsurance (Ark/WM Outrigger) | TPC Providers |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Less: beginning reinsurance recoverable on unpaid losses |  | (145.4) |  |
P&C Insurance Distribution (Bamboo) | Operating Segments |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Gross beginning balance | 0.0 |  |  |
Loss and loss adjustment expenses incurred relating to: |  |  |  |
Net incurred loss and loss adjustment expenses | 5.8 | $ 0.0 |  |
Loss and loss adjustment expenses paid relating to: |  |  |  |
Gross ending balance | $ 12.3 |  |  |

X
- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in the current period and related claims settlement costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in prior periods and related claims settlement costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of foreign currency gain (loss) which decreases (increases) the cost of settling unpaid claims after deduction of reinsurance recoveries. Includes, but is not limited to, claims which have been incurred but not reported. + References No definition available. + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(13)(a)(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 25 -Subparagraph (g) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-25 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_PaymentsForLossesAndLossAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479584/944-310-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479838/944-20-50-5 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 45 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479616/944-310-45-6 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Liability for Unpaid Claims and Claims Adjustment Expense, Third Party Provider + References No definition available. + Details
Name: | wtm_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseThirdPartyProvider
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Reinsurance, Loss and Loss Reserves, Participation Results, Percentage + References No definition available. + Details
Name: | wtm_ReinsuranceLossAndLossReservesParticipationResultsPercentage
Namespace Prefix: | wtm_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
Name: | srt_CounterpartyNameAxis=wtm_TPCProvidersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=wtm_BambooIde8InsuranceServicesLLCSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |