Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2013
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation These interim consolidated financial statements include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) and its subsidiaries (collectively, with the Company, “White Mountains”) and have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its property and casualty insurance and reinsurance subsidiaries and affiliates. The Company’s headquarters is located at 14 Wesley Street, Hamilton, Bermuda HM 11, its principal executive office is located at 80 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. White Mountains’ reportable segments are OneBeacon, Sirius Group, HG Global/BAM and Other Operations. The OneBeacon segment consists of OneBeacon Insurance Group, Ltd. (“OneBeacon Ltd.”), an exempted Bermuda limited liability company that owns a family of property and casualty insurance companies (collectively, “OneBeacon”). OneBeacon is a specialty property and casualty insurance writer that offers a wide range of insurance products in the United States through independent agencies, regional and national brokers, wholesalers and managing general agencies. During the third quarter of 2013, OneBeacon formed Split Rock Insurance, Ltd. (“Split Rock”), a Bermuda-based reinsurance company, to reinsure certain of its risks. As of both September 30, 2013 and December 31, 2012, White Mountains owned 75.2% of OneBeacon Ltd.’s outstanding common shares. As discussed further in Note 2, OneBeacon entered into a definitive agreement to sell its runoff business in October 2012 (the “Runoff Transaction”) and sold its AutoOne Insurance business (“AutoOne”) in February 2012. Accordingly, the runoff business and AutoOne are presented as discontinued operations. Assets and liabilities associated with the runoff business as of September 30, 2013 and December 31, 2012 have been presented as held for sale in the financial statements. Prior year income statement and cash flow amounts have been reclassified to conform to the current year's presentation. (See Note 15 for discontinued operations.) The Sirius Group segment consists of Sirius International Insurance Group, Ltd., an exempted Bermuda limited liability company, and its subsidiaries (collectively, “Sirius Group”). Sirius Group provides insurance and reinsurance products for property, accident and health, aviation and space, trade credit, marine, agriculture and certain other exposures on a worldwide basis through its primary subsidiaries, Sirius International Insurance Corporation (“Sirius International”), Sirius America Insurance Company (“Sirius America”) and Lloyds Syndicate 1945 (“Syndicate 1945”). Sirius Group also specializes in the acquisition and management of runoff insurance and reinsurance companies both in the United States and internationally through its White Mountains Solutions division (“WM Solutions”). The HG Global/BAM segment consists of White Mountains’ investment in HG Global Ltd. (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”). During the third quarter of 2012, White Mountains capitalized HG Global with approximately $600 million to fund the start-up of BAM. BAM is a municipal bond insurer domiciled in New York that was established to provide insurance on bonds issued to support essential U.S. public purposes such as schools, utilities, core governmental functions and existing transportation facilities. HG Global, together with its subsidiaries, provided the initial capitalization of BAM through the purchase of $503 million of surplus notes issued by BAM (the “BAM Surplus Notes”). HG Global, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), also provides 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. As of both September 30, 2013 and December 31, 2012, White Mountains owned 97.3% of HG Global's preferred equity and 88.7% of its common equity. White Mountains does not have an ownership interest in BAM, which is a mutual insurance company owned by its members. However, GAAP requires White Mountains to consolidate BAM's results in its financial statements. BAM's results are attributed to non-controlling interests. White Mountains’ Other Operations segment consists of the Company and its intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), White Mountains’ variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“WM Life Re”), which is in runoff, as well as various other entities not included in other segments. Prior to 2012, the Other Operations segment also included the consolidated results of the Tuckerman Capital, LP fund (“Tuckerman Fund I”). On December 31, 2011, 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, LLC (“Hamer”) and Bri-Mar Manufacturing, LLC (“Bri-Mar”), two small manufacturing companies. Prior to the dissolution, Tuckerman Fund I was consolidated within White Mountains’ financial statements. The consolidated results of Hamer and Bri-Mar are included in the Other Operations segment from January 1, 2012 through September 30, 2012, from which point these companies were no longer consolidated by White Mountains. White Mountains’ discontinued operations consist of OneBeacon's runoff business and AutoOne. The OneBeacon runoff business included assets and liabilities that were principally related to non-specialty commercial lines and certain other runoff business that it no longer writes, including nearly all of its asbestos and environmental reserves. AutoOne was formed by OneBeacon in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey. All significant intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2012 Annual Report on Form 10-K. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. Refer to the Company’s 2012 Annual Report on Form 10-K for a complete discussion regarding White Mountains’ significant accounting policies. Non-controlling Interests Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries and are presented separately on the balance sheet. The percentage of the non-controlling shareholders’ ownership interest in OneBeacon Ltd. at both September 30, 2013 and December 31, 2012 was 24.8%. In July 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from certain management personnel of BAM, the latter of which is included in non-controlling interest. Upon closing, certain BAM management personnel also received additional common and preferred shares of HG Global that resulted in a $2.2 million allocation of the carrying value of White Mountains’ investment in HG Global to the non-controlling interest, which was recorded as an adjustment to paid-in surplus in White Mountains’ consolidated statement of changes in equity. White Mountains is required to consolidate BAM in its GAAP financial statements. However, since BAM is a mutual insurance company that is owned by its members, BAM’s results do not affect White Mountains’ common shareholders’ equity as they are attributable to non-controlling interests. For the three and nine months ended September 30, 2013, BAM reported $11.4 million and $52.4 million in after-tax losses that have been allocated to non-controlling interest. In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250 million non-cumulative perpetual preference shares, with a $1,000 per share liquidation preference (the “SIG Preference Shares”), and received $245.7 million of proceeds, net of $4.3 million of issuance costs and commissions. SIG Preference Shares and dividends thereon are included in non-controlling interest on the balance sheet and on the statement of income and comprehensive income. The SIG Preference Shares have an initial fixed annual dividend rate of 7.506%. In June 2017, the fixed rate will move to a floating rate equal to the greater of (i) 7.506% and (ii) 3-month LIBOR plus 320 bps. In July 2013, SIG executed a 5-year forward LIBOR cap (the “Interest Rate Cap”) for the period from June 2017 to June 2022 to protect against a significant increase in interest rates during that 5-year period. The Interest Rate Cap fixes the annual dividend rate on the SIG Preference Shares from June 2017 to June 2022 at 8.30%. The Interest Rate Cap is recorded in other assets at fair value. Changes in fair value are recorded in other revenue. At September 30, 2013 and December 31, 2012, the non-controlling equity interest in White Mountains’ consolidated limited partnerships was $45.1 million and $41.5 million. At September 30, 2013 and December 31, 2012, the non-controlling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $2.9 million and $2.8 million. On September 30, 2013, Sirius Group purchased the remaining 25.0% ownership in one of its subsidiaries, Passage2Health Limited, and now owns 100.0%. At December 31, 2012, the non-controlling equity interest in Passage2Health Limited was $0.2 million. Recently Adopted Changes in Accounting Principles Policy Acquisition Costs On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred. White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon's collector car and boat business, no longer met the criteria for deferral. During the year ended December 31, 2012, White Mountains recognized $5.6 million of expense related to such previously deferrable acquisition costs that, if White Mountains had adopted ASU 2010-26 retrospectively, would have been recognized during 2011. Fair Value Measurements On January 1, 2012, White Mountains adopted ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. The ASU clarifies existing guidance with respect to the concepts of highest and best use and valuation premise and measuring instruments classified within a reporting entity’s shareholders’ equity. The ASU also clarifies disclosure requirements, requiring disclosure of quantitative information about unobservable inputs used in Level 3 fair value measurements. The ASU also amends existing guidance. In circumstances where a reporting entity manages a portfolio of financial assets and liabilities based on the net market and counterparty credit risk exposures, the ASU permits determination of the fair value of those instruments to be based on the net risk exposure. In addition, the ASU permits the application of premiums or discounts to be applied in a fair value measurement to the extent that market participants would consider them in valuing the financial instruments. The ASU also expands the required disclosures for Level 3 measurements, requiring that reporting entities provide a narrative description of the sensitivity of Level 3 fair value measurements to changes in unobservable inputs and the interrelationships between those inputs, if any. As a result of adopting ASU 2011-04, White Mountains expanded its fair value disclosures. (See Note 5.) Offsetting Assets and Liabilities Effective January 1, 2013, White Mountains adopted ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (ASC 210) and ASU 2013-01, Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities. The new guidance expands the required disclosures in circumstances where either balances have been offset or the right of offset exists to make it easier for financial statement users to evaluate the effect or potential effect of netting arrangements on a reporting entity’s financial position. White Mountains is party to master netting arrangements in connection with derivative instruments held by WM Life Re and Sirius International. As a result of adoption, White Mountains has expanded its disclosures to present the gross amounts of assets and liabilities subject to master netting arrangements along with any related collateral amounts. Recently Issued Accounting Pronouncements Unrecognized Tax Benefits On July 18, 2013, the FASB issued ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (ASC 740). The new ASU requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward or tax credit carryforward rather than as a liability. The exception is in circumstances where a carryfoward is not available to settle the additional taxes that might arise upon disallowance of the tax position under the tax law of the applicable jurisdiction. Prior to the issuance of ASU 2013-11, the guidance for unrecognized tax benefits under ASC 740 did not provide explicit guidance on whether an entity should present an unrecognized tax benefit as a liability or as a reduction of NOL carryforwards or other tax credits. In circumstances where an NOL carryforward is not available to offset settlement of any additional taxes arising from a disallowed tax position, the unrecognized tax benefit should be presented as a liability. The new guidance becomes effective for fiscal periods beginning on or after December 15, 2013 and should be applied prospectively to all unrecognized tax benefits that exist at the effective date. Retrospective adoption is allowed. White Mountains does not expect adoption to significantly affect its balance sheet.

Summary of Significant Accounting Policies

Basis of Presentation

These interim consolidated financial statements include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) and its subsidiaries (collectively, with the Company, “White Mountains”) and have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its property and casualty insurance and reinsurance subsidiaries and affiliates. The Company’s headquarters is located at 14 Wesley Street, Hamilton, Bermuda HM 11, its principal executive office is located at 80 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. White Mountains’ reportable segments are OneBeacon, Sirius Group, HG Global/BAM and Other Operations.

The OneBeacon segment consists of OneBeacon Insurance Group, Ltd. (“OneBeacon Ltd.”), an exempted Bermuda limited liability company that owns a family of property and casualty insurance companies (collectively, “OneBeacon”). OneBeacon is a specialty property and casualty insurance writer that offers a wide range of insurance products in the United States through independent agencies, regional and national brokers, wholesalers and managing general agencies. During the third quarter of 2013, OneBeacon formed Split Rock Insurance, Ltd. (“Split Rock”), a Bermuda-based reinsurance company, to reinsure certain of its risks. As of both September 30, 2013 and December 31, 2012, White Mountains owned 75.2% of OneBeacon Ltd.’s outstanding common shares.

As discussed further in Note 2, OneBeacon entered into a definitive agreement to sell its runoff business in October 2012 (the “Runoff Transaction”) and sold its AutoOne Insurance business (“AutoOne”) in February 2012. Accordingly, the runoff business and AutoOne are presented as discontinued operations. Assets and liabilities associated with the runoff business as of September 30, 2013 and December 31, 2012 have been presented as held for sale in the financial statements. Prior year income statement and cash flow amounts have been reclassified to conform to the current year's presentation. (See Note 15 for discontinued operations.)

The Sirius Group segment consists of Sirius International Insurance Group, Ltd., an exempted Bermuda limited liability company, and its subsidiaries (collectively, “Sirius Group”). Sirius Group provides insurance and reinsurance products for property, accident and health, aviation and space, trade credit, marine, agriculture and certain other exposures on a worldwide basis through its primary subsidiaries, Sirius International Insurance Corporation (“Sirius International”), Sirius America Insurance Company (“Sirius America”) and Lloyds Syndicate 1945 (“Syndicate 1945”). Sirius Group also specializes in the acquisition and management of runoff insurance and reinsurance companies both in the United States and internationally through its White Mountains Solutions division (“WM Solutions”).

The HG Global/BAM segment consists of White Mountains’ investment in HG Global Ltd. (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”). During the third quarter of 2012, White Mountains capitalized HG Global with approximately $600 million to fund the start-up of BAM. BAM is a municipal bond insurer domiciled in New York that was established to provide insurance on bonds issued to support essential U.S. public purposes such as schools, utilities, core governmental functions and existing transportation facilities. HG Global, together with its subsidiaries, provided the initial capitalization of BAM through the purchase of $503 million of surplus notes issued by BAM (the “BAM Surplus Notes”). HG Global, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), also provides 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. As of both September 30, 2013 and December 31, 2012, White Mountains owned 97.3% of HG Global's preferred equity and 88.7% of its common equity. White Mountains does not have an ownership interest in BAM, which is a mutual insurance company owned by its members. However, GAAP requires White Mountains to consolidate BAM's results in its financial statements. BAM's results are attributed to non-controlling interests.

White Mountains’ Other Operations segment consists of the Company and its intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), White Mountains’ variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“WM Life Re”), which is in runoff, as well as various other entities not included in other segments. Prior to 2012, the Other Operations segment also included the consolidated results of the Tuckerman Capital, LP fund (“Tuckerman Fund I”). On December 31, 2011, 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, LLC (“Hamer”) and Bri-Mar Manufacturing, LLC (“Bri-Mar”), two small manufacturing companies. Prior to the dissolution, Tuckerman Fund I was consolidated within White Mountains’ financial statements. The consolidated results of Hamer and Bri-Mar are included in the Other Operations segment from January 1, 2012 through September 30, 2012, from which point these companies were no longer consolidated by White Mountains.

White Mountains’ discontinued operations consist of OneBeacon's runoff business and AutoOne. The OneBeacon runoff business included assets and liabilities that were principally related to non-specialty commercial lines and certain other runoff business that it no longer writes, including nearly all of its asbestos and environmental reserves. AutoOne was formed by OneBeacon in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey.

All significant intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2012 Annual Report on Form 10-K.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. Refer to the Company’s 2012 Annual Report on Form 10-K for a complete discussion regarding White Mountains’ significant accounting policies.

Non-controlling Interests

Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries and are presented separately on the balance sheet.

The percentage of the non-controlling shareholders’ ownership interest in OneBeacon Ltd. at both September 30, 2013 and December 31, 2012 was 24.8%.

In July 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from certain management personnel of BAM, the latter of which is included in non-controlling interest. Upon closing, certain BAM management personnel also received additional common and preferred shares of HG Global that resulted in a $2.2 million allocation of the carrying value of White Mountains’ investment in HG Global to the non-controlling interest, which was recorded as an adjustment to paid-in surplus in White Mountains’ consolidated statement of changes in equity.

White Mountains is required to consolidate BAM in its GAAP financial statements. However, since BAM is a mutual insurance company that is owned by its members, BAM’s results do not affect White Mountains’ common shareholders’ equity as they are attributable to non-controlling interests. For the three and nine months ended September 30, 2013, BAM reported $11.4 million and $52.4 million in after-tax losses that have been allocated to non-controlling interest.

In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250 million non-cumulative perpetual preference shares, with a $1,000 per share liquidation preference (the “SIG Preference Shares”), and received $245.7 million of proceeds, net of $4.3 million of issuance costs and commissions. SIG Preference Shares and dividends thereon are included in non-controlling interest on the balance sheet and on the statement of income and comprehensive income. The SIG Preference Shares have an initial fixed annual dividend rate of 7.506%. In June 2017, the fixed rate will move to a floating rate equal to the greater of (i) 7.506% and (ii) 3-month LIBOR plus 320 bps. In July 2013, SIG executed a 5-year forward LIBOR cap (the “Interest Rate Cap”) for the period from June 2017 to June 2022 to protect against a significant increase in interest rates during that 5-year period. The Interest Rate Cap fixes the annual dividend rate on the SIG Preference Shares from June 2017 to June 2022 at 8.30%. The Interest Rate Cap is recorded in other assets at fair value. Changes in fair value are recorded in other revenue.

At September 30, 2013 and December 31, 2012, the non-controlling equity interest in White Mountains’ consolidated limited partnerships was $45.1 million and $41.5 million. At September 30, 2013 and December 31, 2012, the non-controlling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $2.9 million and $2.8 million. On September 30, 2013, Sirius Group purchased the remaining 25.0% ownership in one of its subsidiaries, Passage2Health Limited, and now owns 100.0%. At December 31, 2012, the non-controlling equity interest in Passage2Health Limited was $0.2 million.

Recently Adopted Changes in Accounting Principles

Policy Acquisition Costs

On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred.

White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon's collector car and boat business, no longer met the criteria for deferral. During the year ended December 31, 2012, White Mountains recognized $5.6 million of expense related to such previously deferrable acquisition costs that, if White Mountains had adopted ASU 2010-26 retrospectively, would have been recognized during 2011.

Fair Value Measurements

On January 1, 2012, White Mountains adopted ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. The ASU clarifies existing guidance with respect to the concepts of highest and best use and valuation premise and measuring instruments classified within a reporting entity’s shareholders’ equity. The ASU also clarifies disclosure requirements, requiring disclosure of quantitative information about unobservable inputs used in Level 3 fair value measurements. The ASU also amends existing guidance. In circumstances where a reporting entity manages a portfolio of financial assets and liabilities based on the net market and counterparty credit risk exposures, the ASU permits determination of the fair value of those instruments to be based on the net risk exposure. In addition, the ASU permits the application of premiums or discounts to be applied in a fair value measurement to the extent that market participants would consider them in valuing the financial instruments. The ASU also expands the required disclosures for Level 3 measurements, requiring that reporting entities provide a narrative description of the sensitivity of Level 3 fair value measurements to changes in unobservable inputs and the interrelationships between those inputs, if any. As a result of adopting ASU 2011-04, White Mountains expanded its fair value disclosures. (See Note 5.)

Offsetting Assets and Liabilities

Effective January 1, 2013, White Mountains adopted ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (ASC 210) and ASU 2013-01, Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities. The new guidance expands the required disclosures in circumstances where either balances have been offset or the right of offset exists to make it easier for financial statement users to evaluate the effect or potential effect of netting arrangements on a reporting entity’s financial position. White Mountains is party to master netting arrangements in connection with derivative instruments held by WM Life Re and Sirius International. As a result of adoption, White Mountains has expanded its disclosures to present the gross amounts of assets and liabilities subject to master netting arrangements along with any related collateral amounts.

Recently Issued Accounting Pronouncements

Unrecognized Tax Benefits

On July 18, 2013, the FASB issued ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (ASC 740). The new ASU requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward or tax credit carryforward rather than as a liability. The exception is in circumstances where a carryfoward is not available to settle the additional taxes that might arise upon disallowance of the tax position under the tax law of the applicable jurisdiction. Prior to the issuance of ASU 2013-11, the guidance for unrecognized tax benefits under ASC 740 did not provide explicit guidance on whether an entity should present an unrecognized tax benefit as a liability or as a reduction of NOL carryforwards or other tax credits. In circumstances where an NOL carryforward is not available to offset settlement of any additional taxes arising from a disallowed tax position, the unrecognized tax benefit should be presented as a liability. The new guidance becomes effective for fiscal periods beginning on or after December 15, 2013 and should be applied prospectively to all unrecognized tax benefits that exist at the effective date. Retrospective adoption is allowed. White Mountains does not expect adoption to significantly affect its balance sheet.