Segment Information

12 Months Ended

Dec. 31, 2025

Segment Reporting [Abstract]

Segment Information

Segment Information

As of December 31, 2025, White Mountains conducted its operations through four reportable segments: (1) Ark/WM Outrigger, (2) HG Global, (3) Kudu and (4) Distinguished, with its remaining operating businesses, holding companies and other assets included in Other Operations. White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the Company’s CODM and the Board of Directors. The Company’s CODM is its Chief Executive Officer. The CODM utilizes each segment's pre-tax income (loss) in assessing each segment's performance and allocating resources. Other measures of segment profitability are also reviewed by the CODM. Significant intercompany transactions among White Mountains’s segments have been eliminated herein.

During the fourth quarter of 2022, Ark sponsored the formation of Outrigger Re Ltd. to provide collateralized reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio written in the 2023 underwriting year. Ark renewed its quota share reinsurance agreement with Outrigger Re Ltd. for the 2024, 2025 and 2026 underwriting years. White Mountains consolidates its segregated account of Outrigger Re Ltd., WM Outrigger Re, in its financial statements. WM Outrigger Re’s quota share reinsurance agreement with GAIL eliminates in White Mountains’s consolidated financial statements. WM Outrigger Re exclusively provides reinsurance protection to Ark. As a result, WM Outrigger Re was aggregated with Ark within the Ark/WM Outrigger segment starting in 2023. See Note 2 — “Significant Transactions.”

Effective July 1, 2024, White Mountains no longer consolidates BAM. Through June 30, 2024, BAM’s results of operations are presented within the HG Global segment. See Note 2 — “Significant Transactions.”

On December 5, 2025, White Mountains completed the Bamboo Sale Transaction. As a result, White Mountains deconsolidated the Bamboo Group on December 5, 2025, and Bamboo is no longer a reportable segment. Through December 5, 2025, Bamboo’s results of operations are presented within the Bamboo segment. White Mountains’s noncontrolling equity interest in the Bamboo SPV is accounted for at fair value in other long-term investments within Other Operations. See Note 2 — “Significant Transactions.”

On September 2, 2025, White Mountains completed the Distinguished Transaction. As a result, White Mountains began consolidating Distinguished in its financial statements on September 2, 2025. See Note 2 — “Significant Transactions.”

The following tables present White Mountains’s pre-tax financial results by segment for the years ended December 31, 2025, 2024 and 2023:

	Ark/WM Outrigger
Millions	Ark			WM Outrigger Re		HG Global		Kudu		Bamboo (1)		Distinguished (2)		Other Operations		Total
Year Ended December 31, 2025
Earned insurance premiums	$	1,612.8		$	84.6	$	30.8	$	—	$	26.7	$	—	$	22.2	$	1,777.1
Net investment income (3)	97.4			9.1		27.1		78.7		2.6		1.0		32.1		248.0
Net realized and unrealized investment gains    (losses) (3)	124.6			—		23.2		103.5		.6		—		80.0		331.9
Net realized and unrealized investment gains    (losses) from investment in MediaAlpha	—			—		—		—		—		—		29.6		29.6
Interest income from BAM Surplus Notes	—			—		29.8		—		—		—		—		29.8
Change in fair value of BAM Surplus Notes	—			—		(37.5)		—		—		—		—		(37.5)
Commission and fee revenues	—			—		—		—		211.4		56.7		16.4		284.5
Net gain on sale of the Bamboo Group	—			—		—		—		—		—		849.3		849.3
Other revenues	15.3			—		.2		1.2		5.0		—		200.6		222.3
Total revenues	1,850.1			93.7		73.6		183.4		246.3		57.7		1,230.2		3,735.0
Loss and loss adjustment expenses	818.8			25.4		—		—		18.0		—		20.0		882.2
Acquisition expenses	371.1			23.1		8.0		—		9.7		—		8.3		420.2
Cost of sales	—			—		—		—		—		—		151.8		151.8
Broker commission expenses	—		—	—		—		—		72.0		22.1		—		94.1
General and administrative expenses (4) (5) (6)	205.0			.1		3.1		17.9		96.8		47.0		236.7		606.6
Change in fair value of contingent consideration	173.0			—		—		—		—		—		—		173.0
Interest expense	17.1			—		17.4		25.9		9.7		5.1		3.2		78.4
Total expenses	1,585.0			48.6		28.5		43.8		206.2		74.2		420.0		2,406.3
Pre-tax income (loss)	$	265.1		$	45.1	$	45.1	$	139.6	$	40.1	$	(16.5)	$	810.2	$	1,328.7

(1) Bamboo’s results are from January 1, 2025 through December 5, 2025, the date of sale.

(2) Distinguished’s results are from September 2, 2025, the date of acquisition, through December 31, 2025.

(3) Net investment income and net realized and unrealized investment gains (losses) for both Bamboo and Distinguished are included in other revenues in the consolidated statement of operations.

(4) Ark’s general and administrative expenses include $143.9 of other underwriting expenses.

(5) Bamboo’s general and administrative expenses include $12.0 of amortization of other intangible assets.

(6) Distinguished’s general and administrative expenses include $7.8 of amortization of other intangible assets.

	Ark/WM Outrigger					HG Global								Other Operations
Millions	Ark			WM Outrigger Re		HG Global		BAM (1)(2)		Kudu		Bamboo				Total
Year Ended December 31, 2024
Earned insurance premiums	$	1,499.8		$	88.0	$	28.9	$	2.8	$	—	$	39.4	$	32.7	$	1,691.6
Net investment income (3)	79.4			11.3		23.4		8.8		66.7		2.2		35.6		227.4
Net realized and unrealized investment gains (losses) (3)	50.1			—		(6.4)		(5.1)		51.3		—		57.0		146.9
Net realized and unrealized investment gains    (losses) from investment in MediaAlpha	—			—		—		—		—		—		38.0		38.0
Interest income (expense) from BAM Surplus Notes	—			—		29.0		(13.2)		—		—		—		15.8
Change in fair value of BAM Surplus Notes	—			—		.5		—		—		—		—		0.5
Unrealized loss on deconsolidation of BAM	—			—		(114.5)		—		—		—		—		(114.5)
Commission and fee revenues	—			—		—		—		—		134.6		14.8		149.4
Other revenues	22.3			—		.1		1.1		.8		3.6		56.8		84.7
Total revenues	1,651.6		1,651.6	99.3		(39.0)		(5.6)		118.8		179.8		234.9		2,239.8
Losses and loss adjustment expenses	825.9			29.9		—		—		—		20.6		12.1		888.5
Acquisition expenses	283.9			23.2		7.8		.4		—		14.1		12.1		341.5
Cost of sales	—			—		—		—		—		—		29.6		29.6
Broker commission expenses	—			—		—		—		—		51.3		—		51.3
General and administrative expenses (4) (5)	208.3			.1		2.2		33.5		15.4		61.1		169.5		490.1
Change in fair value of contingent consideration	61.3			—		—		—		—		—		—		61.3
Interest expense	19.5			—		16.7		—		22.1		—		2.5		60.8
Total expenses	1,398.9			53.2		26.7		33.9		37.5		147.1		225.8		1,923.1
Pre-tax income (loss)	$	252.7		$	46.1	$	(65.7)	$	(39.5)	$	81.3	$	32.7	$	9.1	$	316.7

(1) Effective July 1, 2024, White Mountains no longer consolidates BAM. For the period from January 1, 2024 through June 30, 2024, BAM’s results of operations are presented within the HG Global segment.

(2) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS.

(3) Bamboo’s net investment income and net realized and unrealized investment gains (losses) are included in other revenues in the consolidated statement of operations.

(4) Ark’s general and administrative expenses include $136.1 of other underwriting expenses.

(5) Bamboo’s general and administrative expenses include $16.4 of other underwriting expenses.

	Ark/WM Outrigger				HG Global						Other Operations
Millions	Ark		WM Outrigger Re		HG Global		BAM (1)		Kudu				Total
Year Ended December 31, 2023
Earned insurance premiums	$	1,305.4	$	104.3	$	26.0	$	5.2	$	—	$	—	$	1,440.9
Net investment income	50.4		11.0		17.1		14.6		71.0		30.1		194.2
Net realized and unrealized investment gains (losses)	85.9		—		13.6		13.0		106.1		188.5		407.1
Net realized and unrealized investment gains    (losses) from investment in MediaAlpha	—		—		—		—		—		27.1		27.1
Interest income (expense) from BAM Surplus Notes	—		—		26.2		(26.2)		—		—		—
Commission and fee revenues	—		—		—		—		—		13.2		13.2
Other revenues	.8		—		—		2.9		—		80.5		84.2
Total revenues	1,442.5		115.3		82.9		9.5		177.1		339.4		2,166.7
Loss and loss adjustment expenses	711.2		15.6		—		—		—		—		726.8
Acquisition expenses	251.0		30.5		7.4		1.2		—		—		290.1
Cost of sales	—		—		—		—		—		40.4		40.4
General and administrative expenses (2)	161.7		.3		2.8		66.1		19.4		182.3		432.6
Change in fair value of contingent consideration	48.7		—		—		—		—		—		48.7
Interest expense	21.3		—		16.5		—		21.2		3.7		62.7
Total expenses	1,193.9		46.4		26.7		67.3		40.6		226.4		1,601.3
Pre-tax income (loss)	$	248.6	$	68.9	$	56.2	$	(57.8)	$	136.5	$	113.0	$	565.4

(1)    BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS.

(2)    Ark’s general and administrative expenses include $113.6 of other underwriting expenses.

The following tables present White Mountains’s revenues from external customers by country for the years ended December 31, 2025, 2024 and 2023:

	December 31, 2025
Millions	United States		United Kingdom		Bermuda		Other		Total
Earned insurance premiums	$	26.7	$	1,045.3	$	705.1	$	—	$	1,777.1
Commission and fee revenues	268.1		—		—		16.4		284.5
Other revenues (1)	198.7		—		—		—		198.7
Total	$	493.5	$	1,045.3	$	705.1	$	16.4	$	2,260.3

(1)    Amounts include revenues from external customers related to Enterprise Solutions and certain Other Operating Businesses.

	December 31, 2024
Millions	United States		United Kingdom		Bermuda		Other		Total
Earned insurance premiums	$	2.8	$	956.8	$	732.0	$	—	$	1,691.6
Commission and fee revenues	134.6		—		—		14.8		149.4
Other revenues (1)	55.8		—		—		—		55.8
Total	$	193.2	$	956.8	$	732.0	$	14.8	$	1,896.8

(1)    Amounts include revenues from external customers related to certain Other Operating Businesses.

	December 31, 2023
Millions	United States		United Kingdom		Bermuda		Other		Total
Earned insurance premiums	$	5.2	$	791.7	$	644.0	$	—	$	1,440.9
Commission and fee revenues	—		—		—		13.2		13.2
Other revenues (1)	69.0		—		—		—		69.0
Total	$	74.2	$	791.7	$	644.0	$	13.2	$	1,523.1

(1)    Amounts include revenues from external customers related to certain Other Operating Businesses.

The following table presents White Mountains’s balance sheet information by segment as of December 31, 2025 and 2024:

Millions Selected Balance Sheet Data	Ark/WM Outrigger		HG Global			Kudu		Distinguished		Other Operations			Total
December 31, 2025:
Total investments	$	3,926.5	$	784.2		$	1,313.3	$	94.0	$	2,205.9	(1)	$	8,323.9
Total assets	$	6,354.1	$	1,236.8		$	1,402.3	$	735.4	$	2,577.9	(2)(3)	$	12,306.5
Total liabilities	$	4,528.5	$	499.5	(2)	$	446.9	$	307.1	$	269.4	(2)(3)	$	6,051.4
Redeemable noncontrolling interests	$	—	$	—		$	—	$	131.5	$	—		$	131.5
Total White Mountains’s common    shareholders’ equity	$	1,360.4	$	755.7	(2)	$	814.2	$	223.1	$	2,272.0	(2)	$	5,425.4
Nonredeemable noncontrolling    interests	$	465.2	$	(18.4)		$	141.2	$	73.7	$	36.5		$	698.2
December 31, 2024:
Total investments	$	3,139.7	$	667.6		$	1,041.9	$	—	$	1,568.4	(4)	$	6,417.6
Total assets	$	5,299.0	$	1,179.4	(3)	$	1,108.4	$	—	$	2,338.8	(2)(3)	$	9,925.6
Total liabilities	$	3,664.8	$	464.1	(2)	$	316.7	$	—	$	349.0	(2)(3)	$	4,794.6
Total White Mountains’s common    shareholders’ equity	$	1,223.8	$	728.7	(2)	$	664.1	$	—	$	1,867.1	(2)	$	4,483.7
Nonredeemable noncontrolling    interests	$	410.4	$	(13.4)		$	127.6	$	—	$	122.7		$	647.3

(1) Amount excludes investments of $1.0 related to an Other Operating Business that were reclassified to assets held for sale. See Note 20 — “Held for Sale.”

(2) HG Global preferred dividends payable to White Mountains’s subsidiaries is eliminated in White Mountains’s consolidated financial statements. For segment reporting, the HG Global preferred dividends payable to White Mountains’s subsidiaries included within the HG Global segment are eliminated against the offsetting receivable included within Other Operations and therefore added back to White Mountains’s common shareholders’ equity within the HG Global segment. As of December 31, 2025 and 2024, the HG Global preferred dividends payable to White Mountains’s subsidiaries was $527.2 and $462.1.

(3) Amounts include held for sale balances. See Note 20 — “Held for Sale.”

(4) Amounts exclude investments of $58.0 related to the Bamboo Group and $2.0 related to an Other Operating Business that were reclassified to assets held for sale. See Note 20 — “Held for Sale.”