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Employee Share-Based Incentive Compensation Plans (Tables) | 12 Months Ended
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Dec. 31, 2019
Share-based Payment Arrangement [Abstract] |
Summary of performance share activity | The following table presents performance share activity for the years ended December 31, 2019, 2018 and 2017 for performance shares granted under the WTM Incentive Plan:
|  | Year Ended December 31,
|  | 2019 |  | 2018 |  | 2017
$ in Millions |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 40,616 |  |  | $ | 31.7 |  |  | 50,515 |  |  | $ | 45.8 |  |  | 80,353 |  |  | $ | 42.4 |
Shares paid or expired (1) |  | (13,715 | ) |  | (18.1 | ) |  | (23,186 | ) |  | (28.4 | ) |  | (30,838 | ) |  | (21.9 | )
New grants |  | 15,600 |  |  | — |  |  | 14,105 |  |  | — |  |  | 17,710 |  |  | — |
Forfeitures (2) |  | (28 | ) |  | (.1 | ) |  | (818 | ) |  | .1 |  |  | (16,710 | ) |  | (9.3 | )
Expense recognized |  | — |  |  | 30.2 |  |  | — |  |  | 14.2 |  |  | — |  |  | 34.6 |
End of period (3) |  | 42,473 |  |  | $ | 43.7 |  |  | 40,616 |  |  | $ | 31.7 |  |  | 50,515 |  |  | $ | 45.8 |
(1) | WTM performance shares payments in 2019 for the 2016-2018 performance cycle, which were paid in March 2019 ranged from 139% to 166% of target. WTM performance share payments in 2018 for the 2015-2017 performance cycle, which were paid in March 2018 ranged from 145% to 147% of target. WTM performance share payments in 2017 for the 2014-2016 performance cycle, which were paid in March 2017 ranged from 34% to 76% of target.
(2) | Amounts include changes in assumed forfeitures, as required under GAAP.
(3) Outstanding performance share awards as of December 31, 2017 exclude 2,195 unvested performance shares awards for employees of Sirius Group, which are included in discontinued operations.
Summary of performance shares outstanding and accrued expense for performance shares awarded under an Incentive Plan | The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of December 31, 2019 for each performance cycle:
$ in Millions |  | Target Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2019 – 2021 |  | 15,600 |  |  | $ | 6.0 |
2018 – 2020 |  | 13,450 |  |  | 10.5 |
2017 – 2019 |  | 14,070 |  |  | 27.8 |
Sub-total |  | 43,120 |  |  | 44.3 |
Assumed forfeitures |  | (647 | ) |  | (.6 | )
Total |  | 42,473 |  |  | $ | 43.7 |
Schedule of nonvested restricted stock activity | The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards under the WTM Incentive Plan for the years ended December 31, 2019, 2018 and 2017:
|  | Year Ended December 31,
|  | 2019 |  | 2018 |  | 2017
$ in Millions |  | 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 |  | 41,510 |  |  | $ | 12.5 |  |  | 53,755 |  |  | $ | 14.3 |  |  | 70,620 |  |  | $ | 19.7 |
Issued |  | 15,600 |  |  | 14.5 |  |  | 14,105 |  |  | 11.4 |  |  | 17,985 |  |  | 16.3 |
Vested |  | (13,715 | ) |  | — |  |  | (25,381 | ) |  | — |  |  | (28,846 | ) |  | — |
Forfeited |  | — |  |  | — |  |  | (969 | ) |  | (.2 | ) |  | (6,004 | ) |  | (3.5 | )
Expense recognized |  | — |  |  | (10.3 | ) |  | — |  |  | (13.0 | ) |  | — |  |  | (18.2 | )
End of period (1) |  | 43,395 |  |  | $ | 16.7 |  |  | 41,510 |  |  | $ | 12.5 |  |  | 53,755 |  |  | $ | 14.3 |
(1) Outstanding restricted share awards as of December 31, 2017 include 2,195 unvested restricted shares for employees of Sirius Group

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