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Stock-Based Compensation - Supplemental Information (Details) - USD ($) $ in Millions | 5 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 13, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Stock-Based Compensation |  |  |  |
Minimum tax withholdings |  | $ 19.0 | $ 5.0 | $ 5.0
Compensation Expense |  | 41.0 | 38.0 | 20.0
Tax detriment recognized |  | (4.0) | (5.0) | (4.0)
Unrecognized Total Cost |  | 33.0 |  |
GenOn |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense | $ 1.0 | 1.0 | 6.0 | 4.0
NQSOs |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense |  | 0.0 | 0.0 | 0.0
Unrecognized Total Cost |  | $ 0.0 |  |
Weighted Average Recognition Period Remaining (In years) |  | 0 years |  |
RSUs |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense |  | $ 12.0 | 15.0 | 12.0
Unrecognized Total Cost |  | $ 9.0 |  |
Weighted Average Recognition Period Remaining (In years) |  | 10 months 21 days |  |
Award vesting period |  | 3 years |  |
DSUs |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense |  | $ 2.0 | 2.0 | 2.0
Unrecognized Total Cost |  | $ 0.0 |  |
Weighted Average Recognition Period Remaining (In years) |  | 0 years |  |
MSUs |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense |  | $ 4.0 | 5.0 | 2.0
Unrecognized Total Cost |  | $ 0.0 |  |
Weighted Average Recognition Period Remaining (In years) |  | 11 days |  |
RPSUs |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense |  | $ 7.0 | 3.0 | 0.0
Unrecognized Total Cost |  | $ 10.0 |  |
Weighted Average Recognition Period Remaining (In years) |  | 1 year 3 months 26 days |  |
PRSUs |  |  |  |
Stock-Based Compensation |  |  |  |
Compensation Expense |  | $ 16.0 | $ 13.0 | $ 4.0
Unrecognized Total Cost |  | $ 14.0 |  |
Weighted Average Recognition Period Remaining (In years) |  | 1 year 2 months 1 day |  |
Award vesting period |  | 3 years |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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