XML 106 R89.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Loss and Loss Adjustment Expense Reserves - Schedule of Ending Liabilities for Unpaid Loss and LAE, Net of Reinsurance (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Total Reinsurance recoverables on unpaid losses | $ 428.9 |
Property and Accident & Health |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 175.0 |
Marine & Energy |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 99.3 |
Specialty |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 85.2 |
Casualty - Active |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 37.4 |
Casualty - Runoff |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 68.4 |
Ark |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Unpaid loss and LAE reserves, net of reinsurance recoverables on unpaid losses | 465.8 |
Total Reinsurance recoverables on unpaid losses | 428.9 |
Loss and loss adjustment expense reserves | 894.7 | $ 0.0
Ark | Amount attributable to TPC Providers |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Total Reinsurance recoverables on unpaid losses | 276.8 |
Ark | Property and Accident & Health |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 175.0 |
Total Reinsurance recoverables on unpaid losses | 145.2 |
Ark | Marine & Energy |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 99.3 |
Total Reinsurance recoverables on unpaid losses | 70.2 |
Ark | Specialty |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 85.2 |
Total Reinsurance recoverables on unpaid losses | 68.9 |
Ark | Casualty - Active |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 37.4 |
Total Reinsurance recoverables on unpaid losses | 41.4 |
Ark | Casualty - Runoff |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | 68.4 |
Total Reinsurance recoverables on unpaid losses | 103.2 |
Ark | Other |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |
Loss and LAE reserves, net of reinsurance | $ 0.5 |

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 -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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://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(13)(a)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before valuation allowance of reinsurance recoverables for losses reported to the ceding insurer but not yet paid, and for amounts expected based upon statistical projections and other measures of incurred losses and loss settlement expenses which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489 + Details
Name: | us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=116884468&loc=SL65671315-158438 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=116884468&loc=SL65671311-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ProductOrServiceAxis=wtm_PropertyAndAHMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=wtm_MarineAndEnergyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=wtm_SpecialtyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=wtm_CasualtyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=wtm_CasualtyRunoffMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=wtm_ArkInsuranceHoldingsLimitedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_ProductOrServiceAxis=wtm_OtherBusinessMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |