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Employee Share-Based Incentive Compensation Plans - Performance Shares Granted Under the WTM Incentive Plan (Details) - Performance Share - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
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Share-based compensation arrangement by share-based payment award |  |  |
Target performance shares outstanding (in shares) | 37,595 |  |
Total target performance shares outstanding (in shares) | 37,031 |  |
Accrued Expense | $ 37.0 |  |
Total Accrued Expense | $ 36.4 |  |
W T M Incentive Plan |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Assumed forfeitures (in shares) | (564) |  |
Total target performance shares outstanding (in shares) |  | 39,449 | 40,828
Assumed forfeitures | $ (0.6) |  |
Total Accrued Expense |  | $ 67.5 | $ 42.2
W T M Incentive Plan | 2021 – 2023 |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Target performance shares outstanding (in shares) | 13,475 |  |
Accrued Expense | $ 22.6 |  |
W T M Incentive Plan | 2022 – 2024 |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Target performance shares outstanding (in shares) | 13,225 |  |
Accrued Expense | $ 14.0 |  |
W T M Incentive Plan | 2023 – 2025 |  |  |
Share-based compensation arrangement by share-based payment award |  |  |
Target performance shares outstanding (in shares) | 10,895 |  |
Accrued Expense | $ 0.4 |  |

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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(ii) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Aggregate carrying value as of the balance sheet date of liabilities for incentive compensation arrangements. + References No definition available. + Details
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- Definition Carrying value as of the balance sheet date for performance shares before forfeitures. + References No definition available. + Details
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- Definition This element represents the reduction to accrued expense for assumed forfeitures of performance shares. + References No definition available. + Details
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- Definition This element represents the number of non-vested performance shares before forfeiture assumptions. + References No definition available. + Details
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