XML 169 R107.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Derivatives (Realized and Unrealized Gains (Losses)) (Details) (White Mountains Life Re, USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Variable Annuity Reinsurance [Line Items] |  |  |  |  |  |  |  |
Change in fair value of variable annuity death benefit liabilities, included in general and administrative expenses | $ 10.2 |  | $ 14.2 |  | $ (1.8) |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Change in fair value of derivatives, included in other revenue | (402.0) |  | (339.0) |  | 92.9 |  |  |
Derivative, Fair Value, Net | 69.2 |  | 98.3 |  |  |  |  |
Fixed income/interest rate |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Change in fair value of derivatives, included in other revenue | (108.7) |  | (149.5) |  | 8.9 |  |  |
Derivative, Fair Value, Net | (9.7) |  | 27.1 |  |  |  |  |
Foreign exchange |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Change in fair value of derivatives, included in other revenue | (96.7) |  | (102.3) |  | 29.5 |  |  |
Derivative, Fair Value, Net | 58.0 |  | 52.8 |  |  |  |  |
Equity |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Change in fair value of derivatives, included in other revenue | (196.6) |  | (87.2) |  | 54.5 |  |  |
Derivative, Fair Value, Net | 20.9 |  | 18.4 |  |  |  |  |
Level 3 |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Change in fair value of derivatives, included in other revenue | 136.5 | [1] | 84.0 | [1] | (14.5) | [1] |  |
Derivative, Fair Value, Net | 63.4 | [1] | 140.5 | [1] | 247.1 | [1] | 275.3 | [1]
Level 3 | Projected Surrender Assumption [Member] |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Change in fair value of derivatives, included in other revenue | $ 6.5 |  |  |  | $ 7.2 |  |  |
[1] | Consists of over-the-counter instruments.

X
- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13495-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 + Details
Name: | us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | wtm_DerivativeInstrumentsGainLossRecognizedInIncomeNetAndCarryingValueAbstract
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net increase or decrease in the fair value of the variable annuity death benefit liabilities included in earnings. + References No definition available. + Details
Name: | wtm_GainLossOnLiabilityForDeathBenefit
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | wtm_VariableAnnuityReinsuranceLineItems
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration