XML 40 R73.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Investment Securities (Net Realized and Unrealized Investement Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract] |  |  |
Net realized investment gains, pre-tax | $ 104.5 | $ 68.1 | $ 68.3
Net unrealized investment gains, pre-tax | 57.2 | 50.1 | 5.8
Net realized and unrealized investment gains, pre-tax | 161.7 | 118.2 | 74.1
Income tax expense attributable to net realized and unrealized investment gains | (21.9) | (26.8) | (18.1)
Net realized and unrealized investment gains, after tax | $ 139.8 | $ 91.4 | $ 56.0

X
- Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The sum of the realized and unrealized net gain (loss) on trading securities during the period. + References Reference 1: 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_NetRealizedOrUnrealizedGainLossOnTradingSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Definition The aggregate of the change in unrealized holding gain (loss) and foreign currency gain (loss) included in earnings during the reporting period. + References No definition available. + Details
Name: | wtm_NetUnrealizedGainLossandForeignCurrencyGainLossonTradingSecurities
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Tax on net realized and unrealized gains (loss), trading securities + References No definition available. + Details
Name: | wtm_Taxonnetrealizedandunrealizedgainslosstradingsecurities
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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