XML 62 R52.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Investment Securities - Net Realized and Unrealized Investment Gains (Losses) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized investment gains (losses) | $ (1.6) | $ 9.9 | $ 12.9 | $ 165.4
Net unrealized investment gains (losses) | (47.7) | (374.7) | (274.3) | (393.2)
Net unrealized investment gains (losses) on investment securities held at the end of the period | (18.6) | (396.8) | (113.3) | (325.5)
Gain (loss) on investments, exchange rate effect | (22.6) | (7.0) | (44.4) | (7.4)
Investments Held |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized and unrealized investment gains (losses) | (48.0) | (366.5) | (255.2) | (234.3)
Fixed maturity investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized investment gains (losses) | (4.9) | 1.0 | (10.8) | 3.8
Net unrealized investment gains (losses) | (58.8) | (7.9) | (192.9) | (27.0)
Short-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized investment gains (losses) | (0.1) | (0.3) | (0.4) | 0.0
Net unrealized investment gains (losses) | (2.1) | 0.0 | (2.6) | 0.0
Common equity securities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized investment gains (losses) | 0.0 | 0.0 | 0.0 | 0.4
Net unrealized investment gains (losses) | 4.3 | 1.6 | (6.3) | 7.3
Net unrealized investment gains (losses) on investment securities held at the end of the period | 4.3 | 1.6 | (6.3) | 7.7
Marketing Technology (MediaAlpha) |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized investment gains (losses) | 0.0 | 0.0 | 0.0 | 160.3
Net unrealized investment gains (losses) | (18.6) | (396.8) | (113.3) | (485.8)
Net unrealized investment gains (losses) on investment securities held at the end of the period | (18.6) | (396.8) | (113.3) | (325.5)
Other long-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net realized investment gains (losses) | 3.4 | 9.2 | 24.1 | 0.9
Net unrealized investment gains (losses) | 27.5 | 28.4 | 40.8 | 112.3
Net realized and unrealized investment (losses) gains |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net unrealized investment gains (losses) on investment securities held at the end of the period | (49.3) | (364.8) | (261.4) | (227.8)
TPC Providers |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net unrealized investment gains (losses) on investment securities held at the end of the period | 1.3 | (1.7) | 6.2 | (6.5)
Fixed maturity and short-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net unrealized investment gains (losses) on investment securities held at the end of the period | (65.9) | (7.2) | (206.7) | (23.2)
Net realized and unrealized investment gains (losses) | 0.1 | (5.7) | (3.0) | (6.9)
Fixed maturity and short-term investments | Investments Held |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net unrealized investment gains (losses) on investment securities held at the end of the period | (66.0) | (1.5) | (203.7) | (16.3)
Common equity securities and investment in MediaAlpha |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net unrealized investment gains (losses) on investment securities held at the end of the period | (14.3) | (395.2) | (119.6) | (317.8)
Net realized and unrealized investment gains (losses) | 0.0 | (0.4) | 0.0 | (20.3)
Common equity securities and investment in MediaAlpha | Investments Held |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Net unrealized investment gains (losses) on investment securities held at the end of the period | $ (14.3) | $ (395.6) | $ (119.6) | $ (338.1)

X
- Definition Amount of realized and unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27405-111563 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c),9(a)) -URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227 Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
Name: | us-gaap_GainLossOnInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
Name: | us-gaap_GainLossOnSaleOfInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of realized gain (loss) on investment. + 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 210.7-04.3(a)) -URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 + Details
Name: | us-gaap_RealizedInvestmentGainsLosses
Namespace Prefix: | us-gaap_
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: | us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
Name: | us-gaap_UnrealizedGainLossOnInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Gain (Loss) On Investments, Exchange Rate Effect + References No definition available. + Details
Name: | wtm_GainLossOnInvestmentsExchangeRateEffect
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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

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

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

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

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

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

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