XML 71 R116.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Derivatives Derivatives (Forward Contracts Collateral) (Details) In Millions, unless otherwise specified | Dec. 31, 2013 USD ($) | Dec. 31, 2013 JPY (¥) | Dec. 31, 2013 Forward contracts USD ($) | Dec. 31, 2013 Forward contracts SEK | Dec. 31, 2012 Forward contracts USD ($) | Dec. 31, 2013 Barclays [Member] A Forward contracts USD ($) | Dec. 31, 2012 Barclays [Member] A Forward contracts USD ($) | Dec. 31, 2013 Deutsche Bank [Member] A Forward contracts USD ($) | Dec. 31, 2012 Deutsche Bank [Member] A Forward contracts USD ($) | Dec. 31, 2013 Goldman Sachs [Member] Standard & Poor's, A- Rating [Member] Forward contracts USD ($) | Dec. 31, 2012 Goldman Sachs [Member] Standard & Poor's, A- Rating [Member] Forward contracts USD ($) | Dec. 31, 2013 HSBC Bank plc [Member] Standard & Poor's, AA- Rating [Member] Forward contracts USD ($) | Dec. 31, 2012 HSBC Bank plc [Member] Standard & Poor's, AA- Rating [Member] Forward contracts USD ($) | Dec. 31, 2013 J P Morgan Chase [Member] Standard & Poor's, A+ Rating [Member] Forward contracts USD ($) | Dec. 31, 2012 J P Morgan Chase [Member] Standard & Poor's, A+ Rating [Member] Forward contracts USD ($) | Dec. 31, 2013 Royal Bank of Canada [Member] Standard & Poor's, AA- Rating [Member] Forward contracts USD ($) | Dec. 31, 2012 Royal Bank of Canada [Member] Standard & Poor's, AA- Rating [Member] Forward contracts USD ($)
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amount | $ 1,900.0 | ¥ 203,600.0 | $ 20.4 |  | 131.3 | $ 31.2 | $ 5.8 |  | $ 7.7 | $ 7.7 |  | $ 11.1 | $ 2.1 |  | $ 0.4 | $ 3.3 |  | $ 10.1 | $ 1.3 |  | $ 1.9 | $ 0.2 |  | $ 0
Uncollaterailized Balance of Forward Currency Derivatives |  |  | $ (0.1) | [1] |  | $ (0.1) | $ 0 | [1] | $ (0.1) | $ 0 | [1] | $ 0 | $ 0 | [1] | $ 0 | $ (0.1) | [1] | $ 0 | $ 0 | [1] | $ 0 | $ 0 | [1] | $ 0
[1] | Standard & Poor’s (“S&P”) ratings as detailed above are: “AA-” (Very Strong, which is the sixth highest of twenty-one creditworthiness ratings), “A+” (Strong, which is the seventh highest of twenty-one creditworthiness ratings) and “A” (Strong, which is the eighth highest of twenty-one creditworthiness ratings).

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition Uncollaterailized Balance of Forward Currency Derivatives + References No definition available. + Details
Name: | wtm_UncollaterailizedBalanceOfForwardCurrencyDerivatives
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant