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Employee Share-Based Incentive Compensation Plans (Tables) | 12 Months Ended
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Dec. 31, 2015
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, 2015, 2014 and 2013 for performance shares granted under the WTM Incentive Plan and the WTM Phantom Share Plan:
|  | Year Ended December 31,
|  | 2015 |  | 2014 |  | 2013
$ in millions |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 113,198 |  |  | $ | 44.4 |  |  | 108,605 |  |  | $ | 54.9 |  |  | 108,065 |  |  | $ | 26.5 |
Shares paid or expired(1) |  | (42,958 | ) |  | (30.8 | ) |  | (33,730 | ) |  | (24.5 | ) |  | (43,100 | ) |  | (10.1 | )
New grants |  | 29,828 |  |  | — |  |  | 41,580 |  |  | — |  |  | 43,660 |  |  | — |
Assumed forfeitures and cancellations(2)(3) |  | (3,857 | ) |  | (.3 | ) |  | (3,257 | ) |  | (.1 | ) |  | (20 | ) |  | (.6 | )
Expense recognized |  | — |  |  | 44.4 |  |  | — |  |  | 14.1 |  |  | — |  |  | 39.1 |
End of period (4) |  | 96,211 |  |  | $ | 57.7 |  |  | 113,198 |  |  | $ | 44.4 |  |  | 108,605 |  |  | $ | 54.9 |
(1) | WTM performance share 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. WTM performance shares payments in 2013 for the 2010-2012 performance cycle ranged from 33% to 98% of target.
(2) | On November 19, 2014, the Compensation Committee canceled 3,040 WTM performance shares for the 2014-2016 performance cycle and issued the same number of WTM restricted shares.
(3) | 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 table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of December 31, 2015 for each performance cycle:
$ in millions |  | Target WTM Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2015 – 2017 |  | 29,828 |  |  | $ | 8.3 |
2014 – 2016 |  | 32,557 |  |  | 12.9 |
2013 – 2015 |  | 36,293 |  |  | 38.0 |
Sub-total |  | 98,678 |  |  | 59.2 |
Assumed forfeitures |  | (2,467 | ) |  | (1.5 | )
Total at December 31, 2015 |  | 96,211 |  |  | $ | 57.7 |
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, 2015, 2014 and 2013:
|  | Year Ended December 31,
|  | 2015 |  | 2014 |  | 2013
$ 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 |  | 83,314 |  |  | $ | 14.3 |  |  | 94,130 |  |  | $ | 17.0 |  |  | 69,910 |  |  | $ | 16.8 |
Issued (1) |  | 23,640 |  |  | 15.7 |  |  | 23,440 |  |  | 13.1 |  |  | 25,720 |  |  | 14.4 |
Vested |  | (36,279 | ) |  | — |  |  | (33,205 | ) |  | — |  |  | (1,500 | ) |  | — |
Forfeited |  | — |  |  | — |  |  | (1,051 | ) |  | (.5 | ) |  | — |  |  | — |
Expense recognized |  | — |  |  | (14.3 | ) |  | — |  |  | (15.3 | ) |  | — |  |  | (14.2 | )
End of period (2) |  | 70,675 |  |  | $ | 15.7 |  |  | 83,314 |  |  | $ | 14.3 |  |  | 94,130 |  |  | $ | 17.0 |
(1) | On November 19, 2014, the Compensation Committee canceled 3,040 WTM performance shares for the 2014-2016 performance cycle and issued the same number of WTM restricted shares.
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, 2015, 2014 and 2013 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:
|  | Year Ended December 31,
|  | 2015 |  | 2014 |  | 2013
$ in millions |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense |  | Target Performance Shares Outstanding |  | Accrued Expense
Beginning of period |  | 517,470 |  |  | $ | 3.4 |  |  | 493,421 |  |  | $ | 4.0 |  |  | 563,190 |  |  | $ | 1.2 |
Payments and deferrals(1) |  | (181,290 | ) |  | (1.5 | ) |  | (142,138 | ) |  | (1.0 | ) |  | (238,658 | ) |  | — |
New awards |  | 154,887 |  |  | — |  |  | 165,800 |  |  | — |  |  | 179,000 |  |  | — |
Forfeitures and cancellations(2) |  | (41,632 | ) |  | (.1 | ) |  | 387 |  |  | — |  |  | (10,111 | ) |  | (.1 | )
Expense recognized |  | — |  |  | (.4 | ) |  | — |  |  | .4 |  |  | — |  |  | 2.9 |
End of period |  | 449,435 |  |  | $ | 1.4 |  |  | 517,470 |  |  | $ | 3.4 |  |  | 493,421 |  |  | $ | 4.0 |
(1) | 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. No payments were made in 2013 for the 2010-2012 OneBeacon performance cycle as the performance factor was zero.
(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, 2015 for each performance cycle:
$ in millions |  | Target OneBeacon Performance Shares Outstanding |  | Accrued Expense
Performance cycle: |  |  |  |  |  |
2015 – 2017 |  | 146,659 |  |  | $ | .7 |
2014 – 2016 |  | 142,710 |  |  | .1 |
2013 – 2015 |  | 167,300 |  |  | .6 |
Sub-total |  | 456,669 |  |  | 1.4 |
Assumed forfeitures |  | (7,234 | ) |  | — |
Total at December 31, 2015 |  | 449,435 |  |  | $ | 1.4 |
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, 2015, 2014 and 2013.
|  | Year Ended December 31,
|  | 2015 |  | 2014 |  | 2013
$ 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 |  | 612,500 |  |  | $ | 3.5 |  |  | 915,000 |  |  | $ | 6.5 |  |  | 927,000 |  |  | $ | 9.6 |
Issued |  | 75,950 |  |  | 1.1 |  |  | — |  |  | — |  |  | — |  |  | — |
Vested |  | (296,000 | ) |  | — |  |  | (300,000 | ) |  | — |  |  | (9,000 | ) |  | — |
Forfeited |  | (9,728 | ) |  | (.1 | ) |  | (2,500 | ) |  | — |  |  | (3,000 | ) |  | — |
Expense recognized |  | — |  |  | (2.0 | ) |  | — |  |  | (3.0 | ) |  | — |  |  | (3.1 | )
End of period |  | 382,722 |  |  | $ | 2.5 |  |  | 612,500 |  |  | $ | 3.5 |  |  | 915,000 |  |  | $ | 6.5 |

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