Significant Transactions	9 Months Ended
Significant Transactions	Sep. 30, 2025
Significant Transactions [Abstract]
Significant Transactions	Significant Transactions Bamboo On October 2, 2025, White Mountains, together with Bamboo, entered into a securities purchase agreement (the “Bamboo SPA”) with certain affiliates of funds advised by CVC Capital Partners (“CVC”) to sell a controlling financial interest in the Bamboo Group. Under the terms of the Bamboo SPA, White Mountains will sell approximately 77.0% of its equity interest in Bamboo for cash and retain the remainder (the “Bamboo Sale Transaction”). The Bamboo Sale Transaction values Bamboo at an enterprise value of $1.75 billion. White Mountains expects to receive net cash proceeds of approximately $840.0 million and will retain a $250.0 million interest in Bamboo, representing approximately 15.0% on a fully-diluted/fully-converted basis. As a result of the Bamboo Sale Transaction, the Bamboo Group’s assets and liabilities have been presented as held for sale in White Mountains’s consolidated balance sheet as of September 30, 2025. Amounts as of December 31, 2024 have been reclassified to conform to the current period’s presentation. See Note 19 — “Held for Sale.” The Bamboo Sale Transaction is expected to close in the fourth quarter of 2025. Completion of the Bamboo Sale Transaction is subject to the receipt of certain regulatory approvals and other customary closing conditions. There is no condition with respect to the availability of financing to consummate the Bamboo Sale Transaction. Distinguished On September 2, 2025, White Mountains acquired a controlling financial interest in Distinguished (the “Distinguished Transaction”). White Mountains funded the Distinguished Transaction through a combination of cash on hand and new borrowings by Distinguished. White Mountains paid $224.3 million of cash consideration, and Distinguished borrowed $50.0 million of incremental debt as part of the transaction. The consideration is subject to customary purchase price adjustments. At closing, White Mountains owned 55.5%, inclusive of its 1.7% previously-held interest, of Distinguished on a basic units outstanding basis (43.6% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives). In connection with the closing, certain management incentive units that would have vested upon a change in control were amended to extend the required service period. As a result, White Mountains’s basic ownership interest at closing increased from the reported 51.0%, which included 1.4% for its previously-held interest, to 55.5%. At closing, 4.2% of the basic units outstanding are owned by Distinguished management (24.7% on a fully-diluted/fully-converted basis). As part of the Distinguished Transaction, WM Phoenix GP, LLC, an indirect wholly-owned subsidiary of the Company, became the general partner of Distinguished. As the general partner, White Mountains has control over all activities of Distinguished subject to consent rights held by certain limited partners. As a result, White Mountains will continue to control Distinguished even if its economic interest falls below 50%. See Note 15 — “Variable Interest Entities.” On September 5, 2028, the third anniversary of the closing of the Distinguished Transaction, certain noncontrolling unitholders will have the option to sell additional units representing 31.4% of Distinguished’s basic units outstanding to White Mountains at the same unit price paid in the Distinguished Transaction less aggregate per unit distributions. As of September 30, 2025, the redemption value would be $131.2 million if exercised in full. See Note 13 — “Noncontrolling Interests.” In addition, White Mountains will have the parallel option to purchase such units at 1.35 times the unit price paid in the Distinguished Transaction less aggregate per unit distributions. White Mountains recognized total assets acquired related to the Distinguished Transaction of $726.2 million, including $595.4 million of goodwill and other intangible assets, total liabilities assumed of $231.7 million, including $100.6 million of debt, redeemable noncontrolling interest of $133.2 million and nonredeemable noncontrolling interest of $74.8 million, reflecting provisional acquisition date fair values. In connection with the acquisition, White Mountains incurred transaction costs of $6.8 million in Other Operations. The Distinguished segment’s revenue and earnings since acquisition are presented in Note 14 — “Segment Information.” BroadStreet On July 18, 2025, White Mountains deployed $150.0 million into BroadStreet through the BroadStreet SPV. BroadStreet is an insurance brokerage company with a presence in all 50 U.S. states and ten Canadian provinces. BroadStreet focuses on commercial and personal property & casualty and employee benefits. White Mountains’s unconsolidated limited partnership interest in the BroadStreet SPV is accounted for at fair value using NAV as a practical expedient and is included within other long-term investments. As of September 30, 2025, the fair value of White Mountains’s interest in the BroadStreet SPV was $150.0 million. As of September 30, 2025, White Mountains had a 10.9% limited partnership interest in the BroadStreet SPV and a less than 5% ownership interest in BroadStreet on a look-through basis. See Note 15 — “Variable Interest Entities.” BAM On July 1, 2024, HG Re and BAM amended the terms of the FLRT with respect to certain governance rights held by HG Re. As a result, and in combination with other governance changes at BAM, White Mountains concluded that it no longer has the power to direct BAM’s activities that most significantly impact its economic performance and is no longer BAM’s primary beneficiary. Accordingly, effective July 1, 2024, White Mountains no longer consolidates BAM. See Note 15 — “Variable Interest Entities.” Through June 30, 2024, BAM’s results of operations were presented within the HG Global segment. Upon deconsolidation, the BAM Surplus Notes met the criteria to be accounted for under the fair value option, which White Mountains elected. Accordingly, the BAM Surplus Notes, including accrued interest receivable, were carried at fair value of $387.4 million as of July 1, 2024, which resulted in an unrealized loss on deconsolidation of $114.5 million. This fair value included the impact of a discount for the time value of money, which was previously included in adjusted book value per share as a non-GAAP adjustment to book value per share. See Note 10 — “Municipal Bond Guarantee Reinsurance” for the valuation techniques and inputs utilized to determine the fair value of the BAM Surplus Notes. WM Outrigger Re During the fourth quarter of 2022, Ark sponsored the formation of Outrigger Re Ltd., a Bermuda company registered as a special purpose insurer and segregated accounts company, to provide reinsurance capacity to Ark. Outrigger Re Ltd. was initially capitalized with $250.0 million of preference shares for business written in the 2023 underwriting year, of which White Mountains contributed $205.0 million. The remaining capital was provided by third-party investors. Outrigger Re Ltd. entered into collateralized quota share agreements with GAIL to provide reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio written for the 2023 underwriting year. The proceeds from the issuance of the preference shares were deposited into collateral trust accounts to fund any potential obligations under the reinsurance agreements with GAIL. Outrigger Re Ltd.’s obligations under the reinsurance agreements with GAIL are subject to an aggregate limit equal to the assets in the collateral trusts at any point in time. The terms of the reinsurance agreements are renewable upon the mutual agreement of Ark and the applicable preference shareholder of Outrigger Re Ltd. During the fourth quarter of 2023, Ark renewed Outrigger Re Ltd. for the 2024 underwriting year with $250.0 million of capital. White Mountains rolled over $130.0 million from its commitment to the 2023 underwriting year and received a return of capital of $75.0 million during 2024 as a result of its reduced capital commitment. The remaining capital was provided by third-party investors. During the fourth quarter of 2024, Ark renewed Outrigger Re Ltd. for the 2025 underwriting year with $230.0 million of capital. White Mountains’s total commitment was $150.0 million, of which $130.0 million was rolled over from its commitment to the 2024 underwriting year. The remaining capital was provided by third-party investors. The reduced capacity at Outrigger Re Ltd. was replaced by Ark through traditional quota share reinsurance agreements. White Mountains owns 100% of the preference shares linked to its segregated account, WM Outrigger Re. White Mountains consolidates WM Outrigger Re’s results in its financial statements. WM Outrigger Re’s quota share reinsurance agreement with GAIL eliminates in White Mountains’s consolidated financial statements. See Note 15 — “Variable Interest Entities.” During the nine months ended September 30, 2025, White Mountains received a distribution of $5.9 million from WM Outrigger Re. During the three months ended March 31, 2024, White Mountains received a return of capital of $68.1 million from WM Outrigger Re as a result of its reduced capital commitment relating to the 2024 underwriting year. During the three months ended September 30, 2024, White Mountains received an additional $64.9 million from WM Outrigger Re, reflecting an initial profit distribution from the 2023 underwriting year. During 2024, WM Outrigger Re commuted its reinsurance agreement with GAIL for the 2023 underwriting year. As of September 30, 2025 and December 31, 2024, WM Outrigger Re held investments of $228.4 million and $203.7 million in a collateral trust. Enterprise Solutions On April 1, 2025, White Mountains acquired a controlling financial interest in Enterprise Solutions (the “Enterprise Solutions Transaction”). Enterprise Solutions provides specialty electrical contracting services to commercial and institutional customers. White Mountains funded the Enterprise Solutions Transaction through a combination of cash on hand and new borrowings by Enterprise Solutions. White Mountains paid $58.3 million of cash consideration, which included a post-acquisition contribution of $1.5 million, and Enterprise Solutions borrowed $15.0 million in new debt as part of the transaction. At closing, White Mountains owned 65.5% of Enterprise Solutions on a basic units outstanding basis (59.0% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives). This is the first acquisition by WTM Partners. White Mountains recognized total assets acquired related to Enterprise Solutions of $176.4 million, total liabilities assumed of $74.4 million and noncontrolling interest of $30.6 million, reflecting provisional acquisition date fair values. Total assets acquired included $57.7 million of goodwill and $37.6 million of other intangible assets, reflecting provisional acquisition date fair values. In connection with the acquisition, White Mountains incurred transaction costs of $3.0 million in Other Operations, of which $1.3 million was expensed in the second quarter of 2025. Unaudited supplemental pro forma information White Mountains’s unaudited pro forma revenues were $891.7 million and $2,287.6 million for the three and nine months ended September 30, 2025, which include revenues from Distinguished and Enterprise Solutions as if the acquisitions had occurred on January 1, 2024, compared to $921.7 million and $2,114.2 million for the three and nine months ended September 30, 2024. The pro forma revenues are presented for comparative purposes only and are not necessarily indicative of the operating results that White Mountains would have recognized had the acquisitions actually been completed on January 1, 2024. The pro forma revenues have been calculated after applying White Mountains’s accounting policies and do not include any material, nonrecurring pro forma adjustments. Impacts to White Mountains’s unaudited pro forma earnings were not material to the amounts previously reported.