CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets
Common equity securities, at fair value	$ 437.6	$ 650.0
Other long-term investments	2,589.2	2,150.2
Total investments	6,998.6	6,417.6
Goodwill and other intangible assets	1,392.9	720.3
Total assets	12,345.6	9,925.6
Liabilities
Debt	870.4	562.5
Total liabilities	6,628.5	4,794.6
Redeemable noncontrolling interests	132.4	0.0
White Mountains’s common shareholders’ equity
White Mountains’s common shares at $1 par value per share - authorized 50,000,000 shares; issued and outstanding 2,575,161 and 2,568,148 shares	2.6	2.6
Paid-in surplus	582.0	563.8
Retained earnings	4,183.0	3,919.0
Accumulated other comprehensive income (loss), after-tax:
Net unrealized gains (losses) from foreign currency translation	0.0	(1.7)
Total White Mountains’s common shareholders’ equity	4,767.6	4,483.7
Nonredeemable noncontrolling interests	817.1	647.3
Total equity	5,584.7	5,131.0
Total liabilities, redeemable noncontrolling interests and equity	12,345.6	9,925.6
Other Operations
Assets
Fixed maturity investments, at fair value	159.6	293.7
Common equity securities, at fair value	0.0	224.6
Investment in MediaAlpha, at fair value	203.2	201.6
Short-term investments, at fair value	199.1	260.1
Other long-term investments	698.3	588.4
Total investments	1,260.2	1,568.4
Cash	41.0	37.6
Goodwill and other intangible assets	154.3	64.8
Other assets	146.5	75.8
Total assets	2,270.2	2,338.8
Liabilities
Loss and loss adjustment expense reserves	14.7	12.1
Unearned insurance premiums	9.5	29.0
Debt	35.4	22.0
Accrued incentive compensation	76.0	79.3
Other liabilities	104.1	33.0
Total liabilities	556.3	349.0
Redeemable noncontrolling interests	0.0
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	1,576.4	1,867.1
Nonredeemable noncontrolling interests	137.5	122.7
Other Operations | Bamboo Group
Assets
Total assets held for sale	662.0	585.7
Liabilities
Total liabilities held for sale	312.3	167.7
Other Operations | Other Disposal Group
Assets
Total assets held for sale	6.2	6.5
Liabilities
Total liabilities held for sale	4.3	5.9
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Liabilities
Loss and loss adjustment expense reserves	2,477.9	2,127.5
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments
Assets
Fixed maturity investments, at fair value	1,834.6	1,565.1
Common equity securities, at fair value	437.6	425.4
Short-term investments, at fair value	745.4	601.4
Other long-term investments	676.5	547.8
Total investments	3,694.1	3,139.7
Cash	289.9	141.2
Reinsurance recoverables	924.8	589.0
Insurance premiums receivable	1,149.7	768.6
Deferred acquisition costs	281.2	165.2
Goodwill and other intangible assets	292.5	292.5
Other assets	164.6	202.8
Total assets	6,796.8	5,299.0
Liabilities
Loss and loss adjustment expense reserves	2,477.9	2,127.5
Unearned insurance premiums	1,427.6	853.3
Debt	159.7	154.5
Reinsurance payable	404.7	149.5
Contingent consideration	229.5	155.3
Other liabilities	249.0	224.7
Total liabilities	4,948.4	3,664.8
Redeemable noncontrolling interests	0.0
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	1,367.7	1,223.8
Nonredeemable noncontrolling interests	480.7	410.4
Financial Guarantee (HG Global) | Operating Segments
Assets
Fixed maturity investments, at fair value	686.5	612.1
Short-term investments, at fair value	56.2	55.5
Total investments	742.7	667.6
Cash	0.2	11.5
BAM Surplus Notes, at fair value	396.2	381.7
Insurance premiums receivable	7.7	4.4
Deferred acquisition costs	93.2	86.6
Other assets	26.1	27.6
Total assets	1,266.1	1,179.4
Liabilities
Unearned insurance premiums	316.3	297.3
Debt	147.7	147.4
Other liabilities	24.5	19.4
Total liabilities	488.5	464.1
Redeemable noncontrolling interests	0.0
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	789.5	728.7
Nonredeemable noncontrolling interests	(11.9)	(13.4)
Asset Management (Kudu) | Operating Segments
Assets
Short-term investments, at fair value	24.6	27.9
Other long-term investments	1,214.4	1,014.0
Total investments	1,239.0	1,041.9
Cash	4.8	0.6
Accrued investment income	24.2	18.0
Goodwill and other intangible assets	7.7	8.0
Other assets	23.1	39.9
Total assets	1,298.8	1,108.4
Liabilities
Debt	274.3	238.6
Other liabilities	85.0	78.1
Total liabilities	359.3	316.7
Redeemable noncontrolling interests	0.0
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	804.0	664.1
Nonredeemable noncontrolling interests	135.5	127.6
Specialty Insurance Distribution (Distinguished) | Operating Segments
Assets
Short-term investments, at fair value	62.6	0.0
Total investments	62.6	0.0
Cash	1.5	0.0
Premiums, commissions and fees receivable	42.2	0.0
Goodwill and other intangible assets	595.4	0.0
Other assets	12.0	0.0
Total assets	713.7	0.0
Liabilities
Debt	148.7	0.0
Premiums and commissions payable	67.9	0.0
Other liabilities	59.4	0.0
Total liabilities	276.0	0.0
Redeemable noncontrolling interests	132.4
Accumulated other comprehensive income (loss), after-tax:
Total White Mountains’s common shareholders’ equity	230.0	0.0
Nonredeemable noncontrolling interests	75.3	0.0
P&C Insurance Distribution (Bamboo) | Operating Segments
Liabilities
Loss and loss adjustment expense reserves	$ 28.5	$ 17.8