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Employee Share-Based Incentive Compensation Plans (Tables) | 12 Months Ended
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Dec. 31, 2016
White Mountains |
Share-based compensation arrangement by share-based payment award |
Summary of performance share activity | The following summarizes performance share activity for the years ended December 31, 2016, 2015 and 2014 for performance shares granted under the WTM Incentive Plan:
|  | Year Ended December 31,
|  | 2016 |  | 2015 |  | 2014
$ in millions |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 93,654 |  |  | $ | 57.7 |  |  | 111,257 |  |  | $ | 44.4 |  |  | 108,605 |  |  | $ | 54.9 |
Shares paid or expired(1) |  | (36,294 | ) |  | (41.0 | ) |  | (42,959 | ) |  | (30.8 | ) |  | (33,730 | ) |  | (24.5 | )
New grants |  | 22,615 |  |  | — |  |  | 29,195 |  |  | — |  |  | 39,590 |  |  | — |
Assumed forfeitures and cancellations(2) |  | 378 |  |  | .5 |  |  | (3,839 | ) |  | (.3 | ) |  | (3,208 | ) |  | (.1 | )
Expense recognized |  | — |  |  | 25.2 |  |  | — |  |  | 44.4 |  |  | — |  |  | 14.1 |
End of period (3) |  | 80,353 |  |  | $ | 42.4 |  |  | 93,654 |  |  | $ | 57.7 |  |  | 111,257 |  |  | $ | 44.4 |
(1) | WTM performance share payments in 2016 for the 2013-2015 performance cycle ranged from 140% to 142% of target. WTM performance shares payments in 2015 for the 2012-2014 performance cycle ranged from 91% to 145.5% of target. WTM performance shares payments in 2014 for the 2011-2013 performance cycle ranged from 88% to 131.5% of target.
(2) | Amounts include changes in assumed forfeitures, as required under GAAP.
(3) | Outstanding performance share awards as of December 31, 2016, 2015 and 2014 exclude 7,315, 10,826 and 12,607 unvested performance shares awards for employees of Sirius Group.
Summary of performance shares outstanding and accrued expense for performance shares awarded under an Incentive Plan | The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of December 31, 2016 for each performance cycle:
$ in millions |  | Target WTM Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2016 – 2018 |  | 19,615 |  |  | $ | 5.4 |
2015 – 2017 |  | 31,795 |  |  | 19.1 |
2014 – 2016 |  | 30,167 |  |  | 18.6 |
Sub-total |  | 81,577 |  |  | 43.1 |
Assumed forfeitures |  | (1,224 | ) |  | (.7 | )
Total at December 31, 2016 |  | 80,353 |  |  | $ | 42.4 |
Schedule of Nonvested Restricted Stock Activity [Table Text Block] | The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards under the WTM Incentive Plan for the years ended December 31, 2016, 2015 and 2014:
|  | Year Ended December 31,
|  | 2016 |  | 2015 |  | 2014
$ 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 |  | 70,675 |  |  | $ | 15.7 |  |  | 83,314 |  |  | $ | 14.3 |  |  | 94,130 |  |  | $ | 17.0 |
Issued |  | 25,365 |  |  | 20.2 |  |  | 23,640 |  |  | 15.7 |  |  | 23,440 |  |  | 13.1 |
Vested |  | (24,620 | ) |  | — |  |  | (36,279 | ) |  | — |  |  | (33,205 | ) |  | — |
Forfeited |  | (800 | ) |  | (.3 | ) |  | — |  |  | — |  |  | (1,051 | ) |  | (.5 | )
Expense recognized |  | — |  |  | (15.9 | ) |  | — |  |  | (14.3 | ) |  | — |  |  | (15.3 | )
End of period (1) |  | 70,620 |  |  | $ | 19.7 |  |  | 70,675 |  |  | $ | 15.7 |  |  | 83,314 |  |  | $ | 14.3 |
(1) | Outstanding restricted share awards as of December 31, 2016, 2015 and 2014 include 5,235, 9,205, and 12,477 unvested restricted shares for employees of Sirius Group.
OneBeacon |
Share-based compensation arrangement by share-based payment award |
Summary of performance share activity | The following summarizes activity for the years ended December 31, 2016, 2015 and 2014 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:
|  | Year Ended December 31,
|  | 2016 |  | 2015 |  | 2014
$ in millions |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 449,435 |  |  | $ | 1.4 |  |  | 517,470 |  |  | $ | 3.4 |  |  | 493,421 |  |  | $ | 4.0 |
Payments and deferrals(1) |  | (167,300 | ) |  | (.6 | ) |  | (181,290 | ) |  | (1.5 | ) |  | (142,138 | ) |  | (1.0 | )
New awards |  | 163,150 |  |  | — |  |  | 154,887 |  |  | — |  |  | 165,800 |  |  | — |
Forfeitures and cancellations(2) |  | 7,234 |  |  | — |  |  | (41,632 | ) |  | (.1 | ) |  | 387 |  |  | — |
Expense recognized |  | — |  |  | .8 |  |  | — |  |  | (.4 | ) |  | — |  |  | .4 |
End of period |  | 452,519 |  |  | $ | 1.6 |  |  | 449,435 |  |  | $ | 1.4 |  |  | 517,470 |  |  | $ | 3.4 |
(1) | OneBeacon performance share payments in 2016 for the 2013-2015 performance cycle were at 24.3% of target. OneBeacon performance share payments in 2015 for the 2012-2014 performance cycle were at 45.7% of target. OneBeacon performance share payments in 2014 for the 2011-2013 performance cycle were at 37.1% of target.
(2) | Amounts include changes in assumed forfeitures, as required under GAAP.
Summary of performance shares outstanding and accrued expense for performance shares awarded under an Incentive Plan | The following summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan as of December 31, 2016 for each performance cycle:
$ in millions |  | Target OneBeacon Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2016 – 2018 |  | 163,150 |  |  | $ | .9 |
2015 – 2017 |  | 146,659 |  |  | .7 |
2014 – 2016 |  | 142,710 |  |  | — |
Total at December 31, 2016 |  | 452,519 |  |  | $ | 1.6 |
Schedule of Nonvested Restricted Stock Activity [Table Text Block] | The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the years ended December 31, 2016, 2015 and 2014.
|  | Year Ended December 31,
|  | 2016 |  | 2015 |  | 2014
$ in millions |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value |  | Restricted Shares |  | Unamortized Issue Date Fair Value
Beginning of period |  | 382,722 |  |  | $ | 2.5 |  |  | 612,500 |  |  | $ | 3.5 |  |  | 915,000 |  |  | $ | 6.5 |
Issued |  | 170,650 |  |  | 2.3 |  |  | 75,950 |  |  | 1.1 |  |  | — |  |  | — |
Vested |  | (157,500 | ) |  | — |  |  | (296,000 | ) |  | — |  |  | (300,000 | ) |  | — |
Forfeited |  | — |  |  | — |  |  | (9,728 | ) |  | (.1 | ) |  | (2,500 | ) |  | — |
Expense recognized |  | — |  |  | (2.7 | ) |  | — |  |  | (2.0 | ) |  | — |  |  | (3.0 | )
End of period |  | 395,872 |  |  | $ | 2.1 |  |  | 382,722 |  |  | $ | 2.5 |  |  | 612,500 |  |  | $ | 3.5 |

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