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Stockholders' Equity (Tables) | 12 Months Ended
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Dec. 31, 2020
Equity [Abstract] |
Schedule of Common Stock Activity | The following table summarizes Common Stock activity during the periods presented below:
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
| (In millions)
Shares outstanding at the beginning of the period | 96.9 |  |  | 110.4 |  |  | 105.2 |
Shares issued for preferred share conversions | — |  |  | — |  |  | 25.5 |
Shares issued for vested restricted stock units | 1.3 |  |  | 1.5 |  |  | 1.1 |
Shares issued for disputed claims | — |  |  | — |  |  | 0.1 |
Shares repurchased | (0.4) |  |  | (15.0) |  |  | (21.5) |
Shares outstanding at the end of the period | 97.8 |  |  | 96.9 |  |  | 110.4 |
Summary of Preferred Stock Activity | The following table summarizes the Series A Convertible Preferred Stock activity during the periods presented below:
| Year Ended December 31, 2018
Shares outstanding at the beginning of the period | 13.5 |
Shares converted to Common Stock | (13.5) |
Shares outstanding at the end of the period | — |

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