XML 98 R43.htm IDEA: XBRL DOCUMENT
v3.19.3

Investment Securities (Net Realized Investment Gains (Losses)) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Trading securities, net realized gains | $ 19.6 | $ (10.2) | $ 90.8 | $ (24.9)
Trading securities, Tax on Realized Holding (Losses) Gains on Investments | (0.2) | 2.3 | (9.0) | 11.2
Trading securities realized holding (losses) gain on investments after tax | 19.4 | (7.9) | 81.8 | (13.7)
Foreign Currency Transaction Gains (Losses), Realized | 0.0 | 0.0 | 0.0 | 11.0
Trading Securities, Tax on Realized Foreign Currency Transaction Gains (Losses) Tax | 0.0 | 0.0 | 0.0 | 0.0
Trading securities, realized foreign currency gain (loss) net of tax | 0.0 | 0.0 | 0.0 | 11.0
Net realized investment gains (losses), pre-tax (1) | 19.6 | (10.2) | 90.8 | (13.9)
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | (0.2) | 2.3 | (9.0) | 11.2
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | 19.4 | (7.9) | 81.8 | (2.7)
Fixed maturity investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Trading securities, net realized gains | 1.4 | (5.1) | 3.5 | (27.6)
Foreign Currency Transaction Gains (Losses), Realized | 0.0 | 0.0 | 0.0 | 18.2
Net realized investment gains (losses), pre-tax (1) | 1.4 | (5.1) | 3.5 | (9.4)
Short-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Trading securities, net realized gains |  |  | 0.1 | (0.8)
Foreign Currency Transaction Gains (Losses), Realized |  |  | 0.0 | 0.0
Net realized investment gains (losses), pre-tax (1) |  |  | 0.1 | (0.8)
Common equity securities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Trading securities, net realized gains | 14.0 | (1.5) | 81.4 | 10.5
Foreign Currency Transaction Gains (Losses), Realized | 0.0 | 0.0 | 0.0 | 0.0
Net realized investment gains (losses), pre-tax (1) | 14.0 | (1.5) | 81.4 | 10.5
Other long-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Trading securities, net realized gains | 4.2 | (3.6) | 5.8 | (7.0)
Foreign Currency Transaction Gains (Losses), Realized | 0.0 | 0.0 | 0.0 | (7.2)
Net realized investment gains (losses), pre-tax (1) | $ 4.2 | $ (3.6) | $ 5.8 | $ (14.2)

X
- Definition Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30690-110894 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30700-110894 + Details
Name: | us-gaap_ForeignCurrencyTransactionGainLossRealized
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 gain (loss) realized from securities classified as trading. + References No definition available. + Details
Name: | us-gaap_TradingSecuritiesRealizedGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax + References No definition available. + Details
Name: | wtm_NetRealizedGainLossandForeignCurrencyGainLossonTradingSecuritiesNetofTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities + References No definition available. + Details
Name: | wtm_TaxonNetRealizedGainLossandForeignCurrencyGainLossonTradingSecurities
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Trading Securities, Realized Foreign Currency Gain (Loss) Net of Tax + References No definition available. + Details
Name: | wtm_TradingSecuritiesRealizedForeignCurrencyGainLossNetofTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Trading Securities, Realized Gain (Loss), Total + References No definition available. + Details
Name: | wtm_TradingSecuritiesRealizedGainLossTotal
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Trading Securities Realized Holding Gain (Loss) on Investments after Tax + References No definition available. + Details
Name: | wtm_TradingSecuritiesRealizedHoldingGainLossonInvestmentsafterTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax + References No definition available. + Details
Name: | wtm_TradingSecuritiesTaxonRealizedForeignCurrencyTransactionGainLossTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Trading securities, Tax on Realized Holding Gain (Loss) on Investments + References No definition available. + Details
Name: | wtm_TradingsecuritiesTaxonRealizedHoldingGainLossonInvestments
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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_EquitySecuritiesMember
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: |