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Employee Share-Based Incentive Compensation Plans (Tables) | 9 Months Ended
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Sep. 30, 2024
Share-Based Payment Arrangement [Abstract] |
Summary of performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan | The following table presents the performance share activity for the three and nine months ended September 30, 2024 and 2023 for performance shares granted under the WTM Incentive Plan:
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2024 |  | 2023 |  | 2024 |  | 2023
$ in Millions |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 34,992 |  |  | $ | 52.0 |  |  | 37,031 |  |  | $ | 44.6 |  |  | 37,031 |  |  | $ | 69.4 |  |  | 39,449 |  |  | $ | 67.5 |
Shares paid (1) (2) |  | — |  |  | — |  |  | — |  |  | — |  |  | (13,475) |  |  | (44.9) |  |  | (13,350) |  |  | (40.8) |
New grants |  | — |  |  | — |  |  | — |  |  | — |  |  | 11,405 |  |  | — |  |  | 10,895 |  |  | — |
Forfeitures and cancellations (3) |  | (133) |  |  | — |  |  | — |  |  | — |  |  | (102) |  |  | .3 |  |  | 37 |  |  | .2 |
Expense recognized |  | — |  |  | 3.7 |  |  | — |  |  | 10.5 |  |  | — |  |  | 30.9 |  |  | — |  |  | 28.2 |
End of period |  | 34,859 |  |  | $ | 55.7 |  |  | 37,031 |  |  | $ | 55.1 |  |  | 34,859 |  |  | $ | 55.7 |  |  | 37,031 |  |  | $ | 55.1 |
(1) WTM performance share payments for the 2021-2023 performance cycle were made in March 2024 at 188% of target. (2) WTM performance share payments for the 2020-2022 performance cycle were made in March 2023 at 200% of target. (3) Amounts include changes in assumed forfeitures, as required under GAAP.
Share-based compensation, performance shares award outstanding activity | The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of September 30, 2024 for each performance cycle:
|  | September 30, 2024
$ in Millions |  | Target Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |
2022 – 2024 |  | 13,150 |  |  | $ | 40.7 |
2023 – 2025 |  | 10,835 |  |  | 11.8 |
2024 – 2026 |  | 11,405 |  |  | 4.0 |
Sub-total |  | 35,390 |  |  | 56.5 |
Assumed forfeitures |  | (531) |  |  | (.8) |
Total |  | 34,859 |  |  | $ | 55.7 |
Unrecognized compensation cost for restricted share awards | The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards under the WTM Incentive Plan for the three and nine months ended September 30, 2024 and 2023:
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2024 |  | 2023 |  | 2024 |  | 2023
$ in Millions |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value
Non-vested, |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning of period |  | 35,525 |  |  | $ | 28.8 |  |  | 37,595 |  |  | $ | 24.3 |  |  | 37,595 |  |  | $ | 16.2 |  |  | 38,350 |  |  | $ | 15.5 |
Issued |  | — |  |  | — |  |  | — |  |  | — |  |  | 11,405 |  |  | 20.0 |  |  | 10,895 |  |  | 16.0 |
Vested |  | — |  |  | — |  |  | — |  |  | — |  |  | (13,475) |  |  | — |  |  | (11,650) |  |  | — |
Forfeited |  | (135) |  |  | — |  |  | — |  |  | — |  |  | (135) |  |  | — |  |  | — |  |  | — |
Expense recognized |  | — |  |  | (4.5) |  |  | — |  |  | (4.1) |  |  | — |  |  | (11.9) |  |  | — |  |  | (11.3) |
End of period |  | 35,390 |  |  | $ | 24.3 |  |  | 37,595 |  |  | $ | 20.2 |  |  | 35,390 |  |  | $ | 24.3 |  |  | 37,595 |  |  | $ | 20.2 |

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