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Employee Share-Based Incentive Compensation Plans (Tables) | 6 Months Ended
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Jun. 30, 2021
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 six months ended June 30, 2021 and 2020 for performance shares granted under the WTM Incentive Plan:
|  | Three Months Ended June 30, |  | Six Months Ended June 30,
|  | 2021 |  | 2020 |  | 2021 |  | 2020
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 |  | 40,784 |  |  | $ | 38.2 |  |  | 42,458 |  |  | $ | 9.8 |  |  | 42,458 |  |  | $ | 56.3 |  |  | 42,473 |  |  | $ | 43.7 |
Shares paid (1) |  | — |  |  | — |  |  | — |  |  | — |  |  | (14,117) |  |  | (34.6) |  |  | (14,070) |  |  | (27.7) |
New grants |  | 475 |  |  | — |  |  | — |  |  | — |  |  | 13,475 |  |  | — |  |  | 14,055 |  |  | — |
Forfeitures and cancellations (2) |  | (7) |  |  | (.2) |  |  | — |  |  | — |  |  | (564) |  |  | .2 |  |  | — |  |  | .4 |
Expense recognized |  | — |  |  | 7.7 |  |  | — |  |  | 6.0 |  |  | — |  |  | 23.8 |  |  | — |  |  | (.6) |
End of period |  | 41,252 |  |  | $ | 45.7 |  |  | 42,458 |  |  | $ | 15.8 |  |  | 41,252 |  |  | $ | 45.7 |  |  | 42,458 |  |  | $ | 15.8 |
(1) WTM performance share payments in 2021 for the 2018-2020 performance cycle, which were paid in cash in March 2021 at 200% of target. WTM performance share payments in 2020 for the 2017-2019 performance cycle, which were paid in cash in March 2020, ranged from 174% to 180% 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 June 30, 2021 for each performance cycle:
|  | Six Months Ended June 30, 2021
Millions, except share amounts |  | Target Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |
2019 – 2021 |  | 14,850 |  |  | $ | 28.4 |
2020 – 2022 |  | 13,555 |  |  | 15.6 |
2021 – 2023 |  | 13,475 |  |  | 2.5 |
Sub-total |  | 41,880 |  |  | 46.5 |
Assumed forfeitures |  | (628) |  |  | (.8) |
June 30, 2021 |  | 41,252 |  |  | $ | 45.7 |
Summary of restricted shares activity | The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards for the three and six months ended June 30, 2021 and 2020:
|  | Three Months Ended June 30, |  | Six Months Ended June 30,
|  | 2021 |  | 2020 |  | 2021 |  | 2020
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 |  | 37,805 |  |  | $ | 26.2 |  |  | 43,105 |  |  | $ | 26.6 |  |  | 43,105 |  |  | $ | 15.2 |  |  | 43,395 |  |  | $ | 16.7 |
Issued |  | 475 |  |  | .5 |  |  | — |  |  | — |  |  | 13,475 |  |  | 16.1 |  |  | 14,055 |  |  | 15.1 |
Vested |  | — |  |  | — |  |  | — |  |  | — |  |  | (17,717) |  |  | — |  |  | (14,345) |  |  | — |
Forfeited |  | — |  |  | — |  |  | — |  |  | — |  |  | (583) |  |  | (.6) |  |  | — |  |  | — |
Expense recognized |  | — |  |  | (3.5) |  |  | — |  |  | (3.6) |  |  | — |  |  | (7.5) |  |  | — |  |  | (8.8) |
End of period |  | 38,280 |  |  | $ | 23.2 |  |  | 43,105 |  |  | $ | 23.0 |  |  | 38,280 |  |  | $ | 23.2 |  |  | 43,105 |  |  | $ | 23.0 |

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- Definition Tabular disclosure of the number and weighted-average grant date fair value for outstanding performance shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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