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Employee Share-Based Incentive Compensation Plans (Tables) | 9 Months Ended
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Sep. 30, 2022
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, 2022 and 2021 for performance shares granted under the WTM Incentive Plan:
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2022 |  | 2021 |  | 2022 |  | 2021
Millions, except share amounts |  | 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 |  | 39,449 |  |  | $ | 41.2 |  |  | 41,252 |  |  | $ | 45.7 |  |  | 40,828 |  |  | $ | 42.2 |  |  | 42,458 |  |  | $ | 56.3 |
Shares paid (1) |  | — |  |  | — |  |  | (219) |  |  | (.6) |  |  | (14,625) |  |  | (26.4) |  |  | (14,336) |  |  | (35.2) |
New grants |  | — |  |  | — |  |  | — |  |  | — |  |  | 13,225 |  |  | — |  |  | 13,475 |  |  | — |
Forfeitures and cancellations (2) |  | — |  |  | (.1) |  |  | (205) |  |  | .2 |  |  | 21 |  |  | (.2) |  |  | (769) |  |  | .4 |
Expense recognized |  | — |  |  | 11.9 |  |  | — |  |  | (6.5) |  |  | — |  |  | 37.4 |  |  | — |  |  | 17.3 |
End of period |  | 39,449 |  |  | $ | 53.0 |  |  | 40,828 |  |  | $ | 38.8 |  |  | 39,449 |  |  | $ | 53.0 |  |  | 40,828 |  |  | $ | 38.8 |
(1) Includes WTM performance share payments in 2022 for the 2019-2021 performance cycle, which were paid in March 2022 at 172% of target and WTM performance share payments in 2021 for the 2018-2020 performance cycle, which were paid in March 2021 at 200% of target. (2) 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, 2022 for each performance cycle:
|  | Nine Months Ended September 30, 2022
Millions, except share amounts |  | Target Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |
2020 – 2022 |  | 13,350 |  |  | $ | 31.9 |
2021 – 2023 |  | 13,475 |  |  | 14.7 |
2022 – 2024 |  | 13,225 |  |  | 7.2 |
Sub-total |  | 40,050 |  |  | 53.8 |
Assumed forfeitures |  | (601) |  |  | (.8) |
September 30, 2022 |  | 39,449 |  |  | $ | 53.0 |
Summary of restricted shares activity | Restricted shares are grants of a specified number of common shares that generally vest at the end of a 34-month service period. The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2022 and 2021:
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2022 |  | 2021 |  | 2022 |  | 2021
Millions, except share amounts |  | 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 |  | 38,350 |  |  | $ | 23.0 |  |  | 38,280 |  |  | $ | 23.2 |  |  | 37,850 |  |  | $ | 15.9 |  |  | 43,105 |  |  | $ | 15.2 |
Issued |  | — |  |  | — |  |  | — |  |  | — |  |  | 13,225 |  |  | 13.8 |  |  | 13,475 |  |  | 16.1 |
Vested |  | — |  |  | — |  |  | (219) |  |  | — |  |  | (12,725) |  |  | — |  |  | (17,936) |  |  | — |
Forfeited |  | — |  |  | — |  |  | (211) |  |  | (.2) |  |  | — |  |  | — |  |  | (794) |  |  | (.8) |
Expense recognized |  | — |  |  | (3.8) |  |  | — |  |  | (3.6) |  |  | — |  |  | (10.5) |  |  | — |  |  | (11.1) |
End of period |  | 38,350 |  |  | $ | 19.2 |  |  | 37,850 |  |  | $ | 19.4 |  |  | 38,350 |  |  | $ | 19.2 |  |  | 37,850 |  |  | $ | 19.4 |

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