Variable Interest Entities	12 Months Ended
Dec. 31, 2013
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable Interest Entities	Variable Interest Entities BAM BAM is a newly formed mutual insurance company. As a mutual company BAM is owned by its members and a portion of each member’s policy payments represents a contribution to member’s surplus. During 2012, White Mountains capitalized HG Global to fund BAM through the purchase of $503.0 million of BAM Surplus Notes. The equity at risk funded by BAM’s members is not sufficient to fund its operations without the additional subordinated financial support provided by the BAM Surplus Notes and accordingly, BAM is considered to be a variable interest entity (“VIE”). BAM and HG Global, through its wholly-owned subsidiary, HG Re, entered into a first loss reinsurance treaty (“FLRT”), under which HG Re will provide first loss protection up to 15% of par outstanding on each bond insured by BAM in exchange for 60% of the premium, net of a ceding commission, charged by BAM. HG Re's obligations under the FLRT are satisfied by the assets in two collateral trusts: a Regulation 114 Trust and a Supplemental Trust. Losses required to be reimbursed to BAM by HG Re are subject to an aggregate limit equal to the assets held in the collateral trusts at any point in time. In addition, HG Global has the right to designate two directors for election to BAM’s board of directors. White Mountains is required to consolidate the results of BAM. Since BAM is owned by its members, its equity and results of operations are included in non-controlling interests (see Note 9). Reciprocals Reciprocals are policyholder-owned insurance carriers organized as unincorporated associations. Each policyholder insured by the reciprocal shares risk with the other policyholders. Policyholders share profits and losses in the same proportion as the amount of insurance purchased but are not subject to assessment for net losses of the reciprocal. In 2004, OneBeacon formed Houston General Management Company to provide management services for a fee to a reciprocal, Houston General Insurance Exchange (“HGIE”). During 2004, OneBeacon contributed $2.0 million of capital to HGIE and in 2005, contributed one of its subsidiaries, Houston General Insurance Company (“HGIC”) with assets of $149.4 million and liabilities of $127.6 million, to HGIE. Subsequent to the contribution of HGIC, HGIE issued a surplus note for $23.7 million to OneBeacon. During 2013, HGIE repaid $19.0 million of the interest owed on the surplus note, as well as $1.0 million of the outstanding principal balance. Subsequent to this payment, the surplus note was amended such that the remaining balance was reduced to $4.0 million. The principal and interest on the remaining surplus note is repayable to OneBeacon only with regulatory approval. The obligation to repay principal on the note is subordinated to all other liabilities including obligations to policyholders and claimants for benefits under insurance policies. OneBeacon has no ownership interest in the reciprocal. OneBeacon has determined that HGIE qualifies as a VIE. Furthermore, OneBeacon has determined that it is the primary beneficiary as it has both the power to direct the activities of the VIE that most significantly impact the entity's economic performance and the obligation to absorb losses or receive benefits of the entity that could potentially be significant to the VIE as a result of the management services provided to the reciprocal and the funds loaned to it. Accordingly, OneBeacon consolidates HGIE. At December 31, 2013 and 2012, consolidated amounts related to HGIE included total assets of $2.6 million and $22.6 million and total liabilities of $4.2 million and $43.8 million. At December 31, 2013, the net amount of capital at risk is equal to the surplus note of $4.0 million less the accumulated losses of $1.6 million which includes accrued interest on the surplus note of $0.1 million that eliminates in consolidation. Prospector Funds White Mountains has determined that the Prospector Offshore Fund, Ltd. and Prospector Turtle Fund, Ltd. (collectively, the “Prospector Funds”) are VIEs for which White Mountains is the primary beneficiary and is required to consolidate. At December 31, 2013 and 2012, White Mountains consolidated total assets of $249.2 million and $238.6 million and total liabilities of $90.6 million and $94.4 million of the Prospector Funds. In addition, at December 31, 2013 and 2012, White Mountains recorded non-controlling interest of $46.2 million and $41.5 million in the Prospector Funds. For the years ended December 31, 2013, 2012 and 2011, White Mountains recorded $14.5 million, $9.3 million, and $(1.0) million of income (loss) and $4.0 million, $2.7 million and $(0.2) million of non-controlling interest income (loss) related to the Prospector Funds. At December 31, 2013, the net amount of capital at risk is equal to White Mountains’ investment in the Funds of $112.5 million, which represents White Mountains’ ownership interest of 71.7% in the Prospector Offshore Fund and 68.9% in the Prospector Turtle Fund. Tuckerman Fund I On December 31, 2011, the Tuckerman Capital, LP fund (“Tuckerman Fund I”) was dissolved and all of the net assets of the fund were distributed to the owners of the fund, of which White Mountains owned approximately 94%. In conjunction with the dissolution, White Mountains received a portion of the shares of Hamer and Bri-Mar, two small manufacturing companies that were owned by the Tuckerman Fund I. The consolidated results of Hamer and Bri-Mar are included in the Other Operations segment from January 1, 2012 through September 30, 2012, at which point the results of these companies were no longer consolidated by White Mountains. Prior to the dissolution, White Mountains had determined that Tuckerman Fund I was a VIE for which White Mountains was the primary beneficiary and was required to consolidate Tuckerman Fund I. At December 31, 2011, White Mountains consolidated assets of $17.6 million, liabilities of $9.9 million, non-controlling interests of $3.5 million and $2.2 million of non-controlling interest expense related to the companies distributed by Tuckerman Fund I.

Variable Interest Entities

BAM

BAM is a newly formed mutual insurance company. As a mutual company BAM is owned by its members and a portion of each member’s policy payments represents a contribution to member’s surplus. During 2012, White Mountains capitalized HG Global to fund BAM through the purchase of $503.0 million of BAM Surplus Notes. The equity at risk funded by BAM’s members is not sufficient to fund its operations without the additional subordinated financial support provided by the BAM Surplus Notes and accordingly, BAM is considered to be a variable interest entity (“VIE”).

BAM and HG Global, through its wholly-owned subsidiary, HG Re, entered into a first loss reinsurance treaty (“FLRT”), under which HG Re will provide first loss protection up to 15% of par outstanding on each bond insured by BAM in exchange for 60% of the premium, net of a ceding commission, charged by BAM. HG Re's obligations under the FLRT are satisfied by the assets in two collateral trusts: a Regulation 114 Trust and a Supplemental Trust. Losses required to be reimbursed to BAM by HG Re are subject to an aggregate limit equal to the assets held in the collateral trusts at any point in time. In addition, HG Global has the right to designate two directors for election to BAM’s board of directors. White Mountains is required to consolidate the results of BAM. Since BAM is owned by its members, its equity and results of operations are included in non-controlling interests (see Note 9).

Reciprocals

Reciprocals are policyholder-owned insurance carriers organized as unincorporated associations. Each policyholder insured by the reciprocal shares risk with the other policyholders. Policyholders share profits and losses in the same proportion as the amount of insurance purchased but are not subject to assessment for net losses of the reciprocal.

In 2004, OneBeacon formed Houston General Management Company to provide management services for a fee to a reciprocal, Houston General Insurance Exchange (“HGIE”). During 2004, OneBeacon contributed $2.0 million of capital to HGIE and in 2005, contributed one of its subsidiaries, Houston General Insurance Company (“HGIC”) with assets of $149.4 million and liabilities of $127.6 million, to HGIE. Subsequent to the contribution of HGIC, HGIE issued a surplus note for $23.7 million to OneBeacon. During 2013, HGIE repaid $19.0 million of the interest owed on the surplus note, as well as $1.0 million of the outstanding principal balance. Subsequent to this payment, the surplus note was amended such that the remaining balance was reduced to $4.0 million. The principal and interest on the remaining surplus note is repayable to OneBeacon only with regulatory approval. The obligation to repay principal on the note is subordinated to all other liabilities including obligations to policyholders and claimants for benefits under insurance policies. OneBeacon has no ownership interest in the reciprocal.

OneBeacon has determined that HGIE qualifies as a VIE. Furthermore, OneBeacon has determined that it is the primary beneficiary as it has both the power to direct the activities of the VIE that most significantly impact the entity's economic performance and the obligation to absorb losses or receive benefits of the entity that could potentially be significant to the VIE as a result of the management services provided to the reciprocal and the funds loaned to it. Accordingly, OneBeacon consolidates HGIE.

At December 31, 2013 and 2012, consolidated amounts related to HGIE included total assets of $2.6 million and $22.6 million and total liabilities of $4.2 million and $43.8 million. At December 31, 2013, the net amount of capital at risk is equal to the surplus note of $4.0 million less the accumulated losses of $1.6 million which includes accrued interest on the surplus note of $0.1 million that eliminates in consolidation.

Prospector Funds

White Mountains has determined that the Prospector Offshore Fund, Ltd. and Prospector Turtle Fund, Ltd. (collectively, the “Prospector Funds”) are VIEs for which White Mountains is the primary beneficiary and is required to consolidate. At December 31, 2013 and 2012, White Mountains consolidated total assets of $249.2 million and $238.6 million and total liabilities of $90.6 million and $94.4 million of the Prospector Funds. In addition, at December 31, 2013 and 2012, White Mountains recorded non-controlling interest of $46.2 million and $41.5 million in the Prospector Funds. For the years ended December 31, 2013, 2012 and 2011, White Mountains recorded $14.5 million, $9.3 million, and $(1.0) million of income (loss) and $4.0 million, $2.7 million and $(0.2) million of non-controlling interest income (loss) related to the Prospector Funds. At December 31, 2013, the net amount of capital at risk is equal to White Mountains’ investment in the Funds of $112.5 million, which represents White Mountains’ ownership interest of 71.7% in the Prospector Offshore Fund and 68.9% in the Prospector Turtle Fund.

Tuckerman Fund I

On December 31, 2011, the Tuckerman Capital, LP fund (“Tuckerman Fund I”) was dissolved and all of the net assets of the fund were distributed to the owners of the fund, of which White Mountains owned approximately 94%. In conjunction with the dissolution, White Mountains received a portion of the shares of Hamer and Bri-Mar, two small manufacturing companies that were owned by the Tuckerman Fund I. The consolidated results of Hamer and Bri-Mar are included in the Other Operations segment from January 1, 2012 through September 30, 2012, at which point the results of these companies were no longer consolidated by White Mountains.

Prior to the dissolution, White Mountains had determined that Tuckerman Fund I was a VIE for which White Mountains was the primary beneficiary and was required to consolidate Tuckerman Fund I. At December 31, 2011, White Mountains consolidated assets of $17.6 million, liabilities of $9.9 million, non-controlling interests of $3.5 million and $2.2 million of non-controlling interest expense related to the companies distributed by Tuckerman Fund I.