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Stock-Based Compensation - Supplemental Information (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Stock-Based Compensation |  |  |
Minimum tax withholdings | $ 27 | $ 36 | $ 19
Compensation Expense | 27 | 32 | 41
Tax detriment recognized | (9) | (12) | (4)
Unrecognized Total Cost | 23 |  |
RSUs |  |  |
Stock-Based Compensation |  |  |
Compensation Expense | 9 | 9 | 12
Unrecognized Total Cost | $ 7 |  |
Weighted Average Recognition Period Remaining (In years) | 1 year 1 month 24 days |  |
Award vesting period | 3 years |  |
DSUs |  |  |
Stock-Based Compensation |  |  |
Compensation Expense | $ 2 | 2 | 2
Unrecognized Total Cost | $ 0 |  |
Weighted Average Recognition Period Remaining (In years) | 0 years |  |
MSUs |  |  |
Stock-Based Compensation |  |  |
Compensation Expense | $ 0 | 0 | 4
Unrecognized Total Cost | $ 0 |  |
Weighted Average Recognition Period Remaining (In years) | 3 days |  |
RPSUs |  |  |
Stock-Based Compensation |  |  |
Compensation Expense | $ 10 | 10 | 7
Unrecognized Total Cost | $ 10 |  |
Weighted Average Recognition Period Remaining (In years) | 11 months 12 days |  |
Award vesting period | 3 years |  |
PRSUs |  |  |
Stock-Based Compensation |  |  |
Compensation Expense | $ 6 | $ 11 | $ 16
Unrecognized Total Cost | $ 6 |  |
Weighted Average Recognition Period Remaining (In years) | 1 year 2 months 26 days |  |
Award vesting period | 3 years |  |

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