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Held for Sale and Discontinued Operations - Financial Statement Disclosure (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022 | Dec. 31, 2022 | Dec. 31, 2021
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] |  |  |  |  |  |
Net income (loss) from discontinued operations, net of tax | $ 0.0 | $ 6.4 | $ 0.0 | $ 10.1 |  |
Net (income) loss from discontinued operations attributable to noncontrolling interests | 0.0 | (0.5) | 0.0 | (0.6) |  |
Other comprehensive income (loss) from discontinued operations, net of tax - NSM Group | 0.0 | (4.0) | 0.0 | (5.9) |  |
Net Cash Provided by (Used in) Discontinued Operations [Abstract] |  |  |  |  |  |
Net cash provided from (used for) operations |  |  | 0.0 | 36.7 |  |
Net cash provided from (used for) investing activities |  |  | 0.0 | 7.1 |  |
Net cash used from (used for) financing activities |  |  | 0.0 | (16.9) |  |
Net change in cash during the period |  |  | (100.5) | 235.7 |  |
Cash balances at beginning of period (includes restricted cash balances of $12.2 and $4.5 and excludes discontinued operations cash balances of $0.0 and $111.6) |  |  | 255.0 | 147.7 |  |
Cash balances at end of period (includes restricted cash balances of $13.4 and $7.3 and excludes discontinued operations cash balances of $0.0 and $142.7) | 154.5 | 383.4 | 154.5 | 383.4 |  |
Restricted cash balance | 13.4 | 7.3 | 13.4 | 7.3 | $ 12.2 | $ 4.5
Interest paid |  |  | 11.6 | 6.3 |  |
Net income tax payments |  |  | 27.8 | 3.8 |  |
Discontinued Operations, Held-for-sale | NSM Insurance Group |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] |  |  |  |  |  |
Commission revenues |  | 80.2 |  | 150.3 |  |
Other revenues |  | 22.7 |  | 41.1 |  |
Total revenues |  | 102.9 |  | 191.4 |  |
General and administrative expenses |  | 57.1 |  | 111.1 |  |
Broker commission expenses |  | 24.1 |  | 44.7 |  |
Change in fair value of contingent consideration |  | 0.0 |  | 0.1 |  |
Amortization of other intangible assets |  | 0.0 |  | 9.1 |  |
Interest expense |  | 8.4 |  | 10.5 |  |
Total expenses |  | 89.6 |  | 175.5 |  |
Pre-tax income (loss) from discontinued operations |  | 13.3 |  | 15.9 |  |
Income tax (expense) benefit |  | (6.9) |  | (5.8) |  |
Net income (loss) from discontinued operations, net of tax |  | 6.4 |  | 10.1 |  |
Net (income) loss from discontinued operations attributable to noncontrolling interests |  | (0.5) |  | (0.6) |  |
Total income (loss) from discontinued operations attributable to White Mountains’s common shareholders |  | 5.9 |  | 9.5 |  |
Other comprehensive income (loss) from discontinued operations, net of tax - NSM Group |  | (4.0) |  | (5.9) |  |
Comprehensive income (loss) from discontinued operations |  | 1.9 |  | 3.6 |  |
Other comprehensive (income) loss from discontinued operations attributable to noncontrolling interests |  | 0.2 |  | 0.3 |  |
Comprehensive income (loss) from discontinued operations attributable to White Mountains’s common shareholders |  | 2.1 |  | 3.9 |  |
Net Cash Provided by (Used in) Discontinued Operations [Abstract] |  |  |  |  |  |
Net cash provided from (used for) operations |  |  |  | 36.7 |  |
Net cash provided from (used for) investing activities |  |  |  | 7.1 |  |
Net cash used from (used for) financing activities |  |  |  | (16.9) |  |
Effect of exchange rate changes on cash |  |  |  | 4.2 |  |
Net change in cash during the period |  |  |  | 31.1 |  |
Cash balances at beginning of period (includes restricted cash balances of $12.2 and $4.5 and excludes discontinued operations cash balances of $0.0 and $111.6) |  |  | 0.0 | 111.6 |  |
Cash balances at end of period (includes restricted cash balances of $13.4 and $7.3 and excludes discontinued operations cash balances of $0.0 and $142.7) | $ 0.0 | 142.7 | $ 0.0 | 142.7 |  |
Restricted cash balance |  | $ 108.9 |  | 108.9 |  | $ 89.2
Interest paid |  |  |  | 10.4 |  |
Net income tax payments |  |  |  | $ 0.0 |  |

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