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SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT - CONDENSED STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT |  |  |
Net income (loss) attributable to White Mountains’s common shareholders | $ 1,106.4 | $ 230.4 | $ 509.2
Charges (credits) to reconcile net income to net cash from operations: |  |  |
Net realized and unrealized investment (gains) losses | (361.5) | (184.9) | (434.2)
Amortization of restricted share awards | 18.5 | 16.3 | 15.3
Net other operating activities | 89.6 | (42.1) | (5.5)
Net cash provided from (used for) operations | 550.5 | 586.8 | 404.1
Cash flows from investing activities: |  |  |
Net change in short-term investments | (872.2) | 548.4 | (495.8)
Release of cash (pre-funding) of investment purchases | (30.0) | 0.0 | 70.0
Net cash provided from (used for) investing activities | (666.9) | (447.0) | (543.9)
Cash flows from financing activities: |  |  |
Repurchases and retirement of common shares | (202.6) | (7.9) | (32.7)
Cash dividends paid to common shareholders | (2.6) | (2.5) | (2.6)
Net cash provided from (used for) financing activities | 35.6 | 4.2 | 7.2
Cash balance at beginning of year | 266.4 | 122.4 | 255.0
Cash balance at end of year | 185.6 | 266.4 | 122.4
Net change in (receivables) payables to subsidiaries | 8.1 | (14.4) | 8.4
Purchases of fixed maturity investments | 1,235.2 | 1,677.5 | 592.7
WM Hinson |  |  |
Cash flows from financing activities: |  |  |
Distributions, cash | 875.0 | 47.0 |
Repayments of debt in short-term investments |  |  | 61.7
Proceeds from borrowings | 90.0 | 208.9 | 20.0
Repayments of principal debt | 183.9 | 190.0 | 42.4
Repayments of debt in investments |  |  | 107.6
Repayments of debt in fixed maturity investments |  |  | 45.9
WM Webster |  |  |
Cash flows from financing activities: |  |  |
Distributions, cash |  | 7.5 |
Distributions, short-term investments |  | 4.9 |
WM Madison |  |  |
Cash flows from financing activities: |  |  |
Distributions, cash |  | $ 2.1 |
Ownership subsidiary |  | 3.50% |
WM Taylor |  |  |
Cash flows from financing activities: |  |  |
Distributions, cash |  | $ 300.0 |
Ownership subsidiary |  | 94.20% |
White Mountain Investments Luxembourg |  |  |
Cash flows from financing activities: |  |  |
Purchases of fixed maturity investments |  | $ 8.0 |
Proceeds from borrowings | 235.0 |  | 105.0
HG Global |  |  |
Cash flows from financing activities: |  |  |
Proceeds from borrowings | 4.0 | 15.2 | 7.5
Repayments of principal debt | 4.0 | 19.2 | 9.5
Subsidiary - White Mountains Investments Bermuda |  |  |
Cash flows from financing activities: |  |  |
Distributions, cash | 35.0 | 4.3 |
Contributions, short-term investments and cash | 30.0 |  |
Repayments of debt in short-term investments | 29.9 |  |
Contributions, cash | 0.1 |  |
Distributions, short-term investments |  | 18.7 |
Subsidiary - White Mountain Adams, Inc. |  |  |
Cash flows from financing activities: |  |  |
Contributions, short-term investments and cash |  | 319.5 |
Repayments of debt in short-term investments |  | 17.2 |
Contributions, cash |  | 0.2 |
White Mountains Insurance Group Ltd. |  |  |
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT |  |  |
Net income (loss) attributable to White Mountains’s common shareholders | 1,106.4 | 230.4 | 509.2
Charges (credits) to reconcile net income to net cash from operations: |  |  |
Net realized and unrealized investment (gains) losses | (15.8) | (50.5) | (78.9)
Equity in (earnings) losses from consolidated and unconsolidated subsidiaries, net of tax | (1,159.3) | (232.3) | (489.2)
Net other non-cash reconciling items | (1.1) | (1.1) | (2.6)
Distributions of accumulated earnings from consolidated subsidiaries | 29.9 | 24.2 | 17.3
Net other operating activities | 14.2 | (17.1) | 9.2
Net cash provided from (used for) operations | (7.2) | (30.1) | (19.7)
Cash flows from investing activities: |  |  |
Net change in short-term investments | 41.1 | 133.9 | (63.8)
Purchases of investment securities | 0.0 | (107.9) | (125.0)
Maturities, calls, paydowns and sales of investment securities | 305.6 | 100.0 | 335.4
Purchases of investment securities from subsidiaries | (8.0) | (12.0) | 0.0
Release of cash (pre-funding) of investment purchases | 0.0 | 0.0 | 70.0
Net issuance of debt (to) from subsidiaries | (279.0) | (224.1) | (132.5)
Net repayment of debt to (from) subsidiaries | 187.9 | 209.2 | 31.4
Net distributions from (contributions to) subsidiaries | (34.9) | (58.8) | (60.3)
Net cash provided from (used for) investing activities | 212.7 | 40.3 | 55.2
Cash flows from financing activities: |  |  |
Repurchases and retirement of common shares | (202.6) | (7.9) | (32.7)
Cash dividends paid to common shareholders | (2.6) | (2.5) | (2.6)
Net cash provided from (used for) financing activities | (205.2) | (10.4) | (35.3)
Net change in cash during the year | 0.3 | (0.2) | 0.2
Cash balance at beginning of year | 0.1 | 0.3 | 0.1
Cash balance at end of year | 0.4 | 0.1 | 0.3
Noncash payment in short-term investments |  |  | 10.0
Purchases of fixed maturity investments |  | 12.0 |
Proceeds from borrowings | 50.0 |  |
White Mountains Insurance Group Ltd. | WM Lafayette |  |  |
Cash flows from financing activities: |  |  |
Purchases of fixed maturity investments | 8.0 |  |
White Mountains Insurance Group Ltd. | WM Pierce |  |  |
Cash flows from financing activities: |  |  |
Purchases of fixed maturity investments | $ 9.9 |  |
Subsidiary - WM Birkdale |  |  |
Cash flows from financing activities: |  |  |
Repayments of debt in short-term investments |  |  | 36.9
Purchases of fixed maturity investments |  | $ 4.0 |
Repayments of principal debt |  |  | 20.5
Repayments of debt in investments |  |  | 73.8
Repayments of debt in fixed maturity investments |  |  | $ 36.9

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