XML 94 R74.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Investment Securities Investment Securities (Net Realized Investment Gain (losses) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Investment securities |  |  |
Trading Securities, Realized Gain (Loss) | $ 76.9 | $ 166.8 | $ 95.7
Foreign Currency Transaction Gain (Loss), Realized | 0.4 | 0.0 | (0.2)
Net realized investment gains, pre-tax | 77.3 | 166.8 | 95.5
Trading securities, Tax on Realized Holding Gain (Loss) on Investments | (22.8) | (28.4) | (16.2)
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax | 0.0 | 0.0 | 0.1
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | (22.8) | (28.4) | (16.1)
Trading Securities Realized Holding Gain (Loss) on Investments after Tax | 54.1 | 138.4 | 79.5
Trading Securities, Realized Foreign Currency Gain (Loss) Net of Tax | 0.4 | 0.0 | (0.1)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | 54.5 | 138.4 | 79.4
Fixed maturity investments |  |  |
Investment securities |  |  |
Trading Securities, Realized Gain (Loss) | 1.9 | 5.8 | (0.2)
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | 0.0 | (0.2)
Net realized investment gains, pre-tax | 1.9 | 5.8 | (0.4)
Short-term investments |  |  |
Investment securities |  |  |
Trading Securities, Realized Gain (Loss) |  |  | 0.1
Foreign Currency Transaction Gain (Loss), Realized |  |  | 0.0
Net realized investment gains, pre-tax |  |  | 0.1
Common equity securities |  |  |
Investment securities |  |  |
Trading Securities, Realized Gain (Loss) | 64.4 | 138.0 | 89.4
Foreign Currency Transaction Gain (Loss), Realized | 0.4 | 0.0 | 0.0
Net realized investment gains, pre-tax | 64.8 | 138.0 | 89.4
Other long-term investments |  |  |
Investment securities |  |  |
Trading Securities, Realized Gain (Loss) | 10.6 | 23.0 | 6.4
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | 0.0 | 0.0
Net realized investment gains, pre-tax | $ 10.6 | $ 23.0 | $ 6.4

X
- Definition Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30690-110894 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6450189&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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 + 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_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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