XML 32 R81.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Investments in Unconsolidated Affiliates (Details) (USD $) In Millions, unless otherwise specified |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2012 | Dec. 31, 2011 | Sep. 30, 2012 Symetra | Sep. 30, 2011 Symetra | Sep. 30, 2012 Symetra | Sep. 30, 2011 Symetra | Dec. 31, 2011 Symetra | Jun. 30, 2012 Symetra | Mar. 31, 2012 Symetra | Dec. 31, 2010 Symetra | Sep. 30, 2012 Symetra Common shareholders' equity. | Jun. 30, 2012 Symetra Common shareholders' equity. | Dec. 31, 2011 Symetra Common shareholders' equity. | Sep. 30, 2011 Symetra Common shareholders' equity. | Jun. 30, 2011 Symetra Common shareholders' equity. | Dec. 31, 2010 Symetra Common shareholders' equity. | Sep. 30, 2012 Symetra Warrants | Mar. 31, 2012 Symetra Warrants | Dec. 31, 2011 Symetra Warrants | Sep. 30, 2011 Symetra Warrants | Mar. 31, 2011 Symetra Warrants | Dec. 31, 2010 Symetra Warrants | Sep. 30, 2012 Pentelia Capital Management | Dec. 31, 2011 Pentelia Capital Management
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Symetra Common Shares excluding unrealized gains (losses) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 284.0 |  |  | $ 261.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total investments in unconsolidated affiliates | 376.3 | 275.3 | 374.8 | [1],[2] | 456.7 | [1],[2] | 374.8 | [1],[2] | 456.7 | [1],[2] | 273.6 | 421.0 | 335.7 | 387.5 | 348.6 | [1],[2] | 305.9 | 261.0 | 449.0 | [1],[2] | 388.5 | 350.4 | 26.2 | [1],[2] | 29.8 | 12.6 | 7.7 | [1],[2] | 32.5 | 37.1 | 1.5 | 1.7
Equity in Unrealized Gains (Losses) from Investments in Unconsolidated Affiliates |  |  | $ 35.2 |  | $ 147.7 |  | $ 64.6 |  | $ 147.7 |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $64.6 and $147.7 as of September 30, 2012 and 2011, which exclude tax expense of $5.2 and $24.2.
[2] | The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share at September 30, 2012.

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

X
- Definition Represents the equity in unrealized gains or losses from investments in unconsolidated affiliates. + References No definition available. + Details
Name: | wtm_EquityInUnrealizedGainsLossesFromInvestmentsInUnconsolidatedAffiliates
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Total investments in (A) companies that are accounted for using the equity method and (B) warrants to acquire additional shares of an unconsolidated affiliate that are carried at fair value. + References No definition available. + Details
Name: | wtm_InvestmentsInUnconsolidatedAffiliates
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Symetra Common Shares excluding unrealized gains (losses) from fixed maturities. + References No definition available. + Details
Name: | wtm_SymetraCommonSharesExcludingUnrealizedGainsLosses
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant