XML 105 R56.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Significant Transactions (Dispositions) (Details) - USD ($) |  |  |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Feb. 26, 2019 | Sep. 28, 2017 | Jul. 21, 2016 | Apr. 18, 2016 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Sep. 30, 2018 | Sep. 28, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales of unconsolidated affiliates and consolidated subsidiaries, net of cash sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 1,131,000,000.0
Gain (loss) on sale of other discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 800,000 | (17,200,000) | 557,000,000.0
Other comprehensive (loss) income, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (1,400,000) | (4,800,000) | 300,000
Net income from discontinued operations, net of tax |  |  |  |  | $ (800,000) | $ 900,000 | $ 0 | $ 700,000 | $ 0 | $ (17,300,000) | $ 0 | $ 100,000 |  |  | 0 | 0 | 20,500,000
Tranzact |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from dividends received |  |  | $ 221,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
MediaAlpha |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from dividends received | $ 89,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Realized gain from transaction |  |  |  |  |  |  |  | 67,500,000 |  |  |  |  |  |  | 67,500,000 |  |
Ownership interest (as a percent) | 48.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fully diluted ownership interest (as a percent) | 42.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assets, fair value |  |  |  |  |  |  |  | 114,700,000 |  |  |  |  |  |  |  |  |
Unrealized investment gain |  |  |  |  |  |  |  | $ 114,700,000 |  |  |  |  |  |  | 180,000,000.0 |  |
Total realized and unrealized gain on sale of minority stake |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 182,200,000 |  |
OneBeacon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of Stock, Price Per Share |  | $ 18.10 |  |  |  |  |  |  |  |  |  |  |  | $ 18.10 |  |  |
Sales of unconsolidated affiliates and consolidated subsidiaries, net of cash sold |  | $ 1,300,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of other discontinued operations, net of tax |  | 554,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive (loss) income, net of tax |  | $ 2,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income from discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 20,500,000 |  |  |
Tranzact |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales of unconsolidated affiliates and consolidated subsidiaries, net of cash sold |  |  | $ 221,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of other discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,200,000 | 3,200,000
Sirius Group |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sales of unconsolidated affiliates and consolidated subsidiaries, net of cash sold |  |  |  | $ 2,600,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of other discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (17,300,000) |
Disposal group, consideration |  |  |  | $ 2,600,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Discontinued Operations | OneBeacon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of other discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 554,500,000
Net income from discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,500,000
Discontinued Operations | Tranzact |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of other discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,200,000
Net income from discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0
Discontinued Operations | Sirius Group |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of other discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 800,000 | $ (17,200,000) | (700,000)
Net income from discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0
Swedish Tax Authority | Sirius Group | Sirius Group |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income from discontinued operations, net of tax |  |  |  |  |  |  |  |  |  |  |  |  | $ (17,300,000) |  | $ 800,000 |  |
MediaAlpha |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  | 48.30% |  |  |  |  |  |  |  |  |  | 48.30% |  |

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after tax of gain (loss) not previously recognized resulting from the disposal of a discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e957-107759 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109222650&loc=d3e1361-107760 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=109222160&loc=SL51721525-107759 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5C -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721675-107760 + Details
Name: | us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation. + References No definition available. + Details
Name: | us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(a)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)) -URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(b)(9)(a)) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(b)(7)(c)) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 + Details
Name: | us-gaap_GainOnSaleOfInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount after tax of income (loss) from a discontinued operation including the portion attributable to the noncontrolling interest. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(12)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=109222160&loc=SL51721525-107759 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5C -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721675-107760 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e957-107759 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109222650&loc=d3e1361-107760 Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(21)) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3A -URI http://asc.fasb.org/extlink&oid=109222160&loc=SL51721523-107759 Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e1012-107759 + Details
Name: | us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount after tax and reclassification adjustments of other comprehensive income (loss). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669619-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=118951672&loc=d3e1436-108581 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669625-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash inflow associated with the deconsolidation of a previously consolidated subsidiary or sale of an entity that is related to it but not strictly controlled. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromDivestitureOfInterestInSubsidiariesAndAffiliates
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Dividends received on equity and other investments during the current period. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 16 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3337-108585 + Details
Name: | us-gaap_ProceedsFromDividendsReceived
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction. + References No definition available. + Details
Name: | us-gaap_SaleOfStockPricePerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the equity in unrealized gains or losses from investments in unconsolidated affiliates. + References No definition available. + Details
Name: | wtm_EquityInUnrealizedGainsLossesFromInvestmentsInUnconsolidatedAffiliates
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Equity Method Investment, Fully Diluted Ownership Percentage + References No definition available. + Details
Name: | wtm_EquityMethodInvestmentFullyDilutedOwnershipPercentage
Namespace Prefix: | wtm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Realized Gain From Transaction + References No definition available. + Details
Name: | wtm_RealizedGainFromTransaction
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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: | wtm_SignificantTransactionsLineItems
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

X
- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=wtm_OnebeaconMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=wtm_TranzactMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=wtm_SiriusGroupMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_SegmentDiscontinuedOperationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeTaxAuthorityAxis=wtm_SwedishTaxAuthorityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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