Basis of Presentation (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic)	9 Months Ended
Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic)	Basis of Presentation (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic) GenOn Energy, Inc., a wholly owned subsidiary of NRG, is a wholesale power generator engaged in the ownership and operation of power generation facilities, with 15,395 MW of net electric generating capacity located in the U.S. On January 1, 2017, GenOn Americas Generation deactivated Pittsburg which resulted in the decrease in operating generation capacity of 1,029 MW from December 31, 2016. GenOn Americas Generation is a wholesale power generator with 6,878 MW of net electric generating capacity located, in many cases, near major metropolitan areas. GenOn Americas Generation's electric generating capacity is part of the 15,395 MW of net electric generating capacity of GenOn. GenOn Mid-Atlantic operates and owns or leases 4,605 MW of net electric generating capacity in Maryland near Washington, D.C. GenOn Mid-Atlantic’s electric generating capacity is part of the 6,878 MW of net electric generating capacity of GenOn Americas Generation. GenOn Mid-Atlantic’s generating stations serve the Eastern PJM markets. GenOn Americas Generation and GenOn Mid-Atlantic are Delaware limited liability companies and indirect wholly owned subsidiaries of GenOn. GenOn Mid-Atlantic is an indirect wholly owned subsidiary of GenOn Americas Generation. The Registrants sell power from their generation portfolio, offer capacity or similar products to retail electric providers and others, and provide ancillary services to support system reliability. Chapter 11 Cases As further described in Note 3, Chapter 11 Cases, on June 14, 2017, GenOn, along with GenOn Americas Generation and certain of their directly and indirectly-owned subsidiaries, or collectively the GenOn Entities, filed voluntary petitions for relief under Chapter 11, or the Chapter 11 Cases, of the United States Bankruptcy Code, or the Bankruptcy Code, in the United States Bankruptcy Court for the Southern District of Texas, Houston Division, or the Bankruptcy Court. GenOn Mid-Atlantic, as well as its consolidated subsidiaries, REMA and certain other subsidiaries, did not file for relief under Chapter 11. The GenOn Entities remain in possession of their property and continue their business operations in the ordinary course uninterrupted as "debtors-in-possession" under jurisdiction of the Bankruptcy Court and in accordance with the applicable provisions of the Bankruptcy Code and orders of the Bankruptcy Court. The consolidated financial statements for GenOn and GenOn Americas Generation were prepared in accordance with Accounting Standards Codification (ASC) 852, Reorganizations, for debtors-in-possession. On June 29, 2017, the GenOn Entities filed a Joint Plan of Reorganization pursuant to Chapter 11 of the Bankruptcy Code (as may be amended, modified or supplemented from time to time), or the Plan, and a related Disclosure Statement, or the Disclosure Statement, with the Bankruptcy Court consistent with the restructuring support and lock-up agreement, or Restructuring Support Agreement, by and among the GenOn Entities, NRG, certain holders representing greater than 93% in aggregate principal amount of GenOn’s Senior Notes and certain holders representing greater than 93% in aggregate principal amount of GenOn Americas Generation’s Senior Notes, as further described in Note 3, Chapter 11 Cases. Liquidity and Ability to Continue as a Going Concern As described above and in Note 3, Chapter 11 Cases, the GenOn Entities have submitted the Plan in connection with the Chapter 11 Cases. There is no assurance that such Plan will be approved by the requisite stakeholders, confirmed by the Bankruptcy Court, or successfully implemented thereafter. GenOn's and GenOn Americas Generation’s ability to continue as a going concern is dependent on many factors, including the successful confirmation of the Plan and emergence from bankruptcy. Given the uncertainty as to the outcome of these factors, there is substantial doubt about GenOn's and GenOn Americas Generation's ability to continue as a going concern. The accompanying unaudited interim condensed consolidated financial statements have been prepared assuming GenOn will continue as a going concern, which contemplates continuity of operations, realization of assets and the satisfaction of liabilities in the normal course of business. As such, the accompanying unaudited interim condensed consolidated financial statements do not include any adjustments relating to the recoverability and classification of assets and their carrying amounts, or the amount and classification of liabilities that may result should GenOn be unable to continue as a going concern. Such adjustments could have a material adverse impact on GenOn's results of operations, cash flows and financial position. With respect to GenOn Mid-Atlantic, a consolidated subsidiary of GenOn, management has determined that while it has sufficient cash on hand to fund current obligations including operating lease payments due under the GenOn Mid-Atlantic operating leases as of September 30, 2017, the potential significant adverse impact of financial stresses at GenOn Mid-Atlantic's parent companies and any adverse impact resulting from the notification by GenOn Mid-Atlantic's owner lessors alleging the existence of certain lease events of default as further described in Note 8, Debt and Capital Leases, has caused there to be substantial doubt about GenOn Mid-Atlantic's ability to continue as a going concern. Basis of Presentation This is a combined quarterly report of the Registrants for the quarter ended September 30, 2017. The notes to the condensed consolidated financial statements apply to the Registrants as indicated parenthetically next to each corresponding disclosure. The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the SEC's regulations for interim financial information and with the instructions to Form 10-Q. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The following notes should be read in conjunction with the accounting policies and other disclosures as set forth in the notes to the financial statements in the Registrants' 2016 Form 10-K. Interim results are not necessarily indicative of results for a full year. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all material adjustments consisting of normal and recurring accruals necessary to present fairly the Registrants' consolidated financial positions as of September 30, 2017, and the results of operations, comprehensive income/(loss) and cash flows for the three and nine months ended September 30, 2017 and 2016. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates. Reclassifications Certain prior year amounts have been reclassified for comparative purposes. The reclassifications did not affect results from operations, net assets or cash flows.

Basis of Presentation (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic)

GenOn Energy, Inc., a wholly owned subsidiary of NRG, is a wholesale power generator engaged in the ownership and operation of power generation facilities, with 15,395 MW of net electric generating capacity located in the U.S. On January 1, 2017, GenOn Americas Generation deactivated Pittsburg which resulted in the decrease in operating generation capacity of 1,029 MW from December 31, 2016.

GenOn Americas Generation is a wholesale power generator with 6,878 MW of net electric generating capacity located, in many cases, near major metropolitan areas. GenOn Americas Generation's electric generating capacity is part of the 15,395 MW of net electric generating capacity of GenOn.

GenOn Mid-Atlantic operates and owns or leases 4,605 MW of net electric generating capacity in Maryland near Washington, D.C. GenOn Mid-Atlantic’s electric generating capacity is part of the 6,878 MW of net electric generating capacity of GenOn Americas Generation. GenOn Mid-Atlantic’s generating stations serve the Eastern PJM markets.

GenOn Americas Generation and GenOn Mid-Atlantic are Delaware limited liability companies and indirect wholly owned subsidiaries of GenOn. GenOn Mid-Atlantic is an indirect wholly owned subsidiary of GenOn Americas Generation.

The Registrants sell power from their generation portfolio, offer capacity or similar products to retail electric providers and others, and provide ancillary services to support system reliability.

Chapter 11 Cases

As further described in Note 3, Chapter 11 Cases, on June 14, 2017, GenOn, along with GenOn Americas Generation and certain of their directly and indirectly-owned subsidiaries, or collectively the GenOn Entities, filed voluntary petitions for relief under Chapter 11, or the Chapter 11 Cases, of the United States Bankruptcy Code, or the Bankruptcy Code, in the United States Bankruptcy Court for the Southern District of Texas, Houston Division, or the Bankruptcy Court. GenOn Mid-Atlantic, as well as its consolidated subsidiaries, REMA and certain other subsidiaries, did not file for relief under Chapter 11.

The GenOn Entities remain in possession of their property and continue their business operations in the ordinary course uninterrupted as "debtors-in-possession" under jurisdiction of the Bankruptcy Court and in accordance with the applicable provisions of the Bankruptcy Code and orders of the Bankruptcy Court. The consolidated financial statements for GenOn and GenOn Americas Generation were prepared in accordance with Accounting Standards Codification (ASC) 852, Reorganizations, for debtors-in-possession.

On June 29, 2017, the GenOn Entities filed a Joint Plan of Reorganization pursuant to Chapter 11 of the Bankruptcy Code (as may be amended, modified or supplemented from time to time), or the Plan, and a related Disclosure Statement, or the Disclosure Statement, with the Bankruptcy Court consistent with the restructuring support and lock-up agreement, or Restructuring Support Agreement, by and among the GenOn Entities, NRG, certain holders representing greater than 93% in aggregate principal amount of GenOn’s Senior Notes and certain holders representing greater than 93% in aggregate principal amount of GenOn Americas Generation’s Senior Notes, as further described in Note 3, Chapter 11 Cases.

Liquidity and Ability to Continue as a Going Concern

As described above and in Note 3, Chapter 11 Cases, the GenOn Entities have submitted the Plan in connection with the Chapter 11 Cases. There is no assurance that such Plan will be approved by the requisite stakeholders, confirmed by the Bankruptcy Court, or successfully implemented thereafter. GenOn's and GenOn Americas Generation’s ability to continue as a going concern is dependent on many factors, including the successful confirmation of the Plan and emergence from bankruptcy. Given the uncertainty as to the outcome of these factors, there is substantial doubt about GenOn's and GenOn Americas Generation's ability to continue as a going concern.

The accompanying unaudited interim condensed consolidated financial statements have been prepared assuming GenOn will continue as a going concern, which contemplates continuity of operations, realization of assets and the satisfaction of liabilities in the normal course of business. As such, the accompanying unaudited interim condensed consolidated financial statements do not include any adjustments relating to the recoverability and classification of assets and their carrying amounts, or the amount and classification of liabilities that may result should GenOn be unable to continue as a going concern. Such adjustments could have a material adverse impact on GenOn's results of operations, cash flows and financial position.

With respect to GenOn Mid-Atlantic, a consolidated subsidiary of GenOn, management has determined that while it has sufficient cash on hand to fund current obligations including operating lease payments due under the GenOn Mid-Atlantic operating leases as of September 30, 2017, the potential significant adverse impact of financial stresses at GenOn Mid-Atlantic's parent companies and any adverse impact resulting from the notification by GenOn Mid-Atlantic's owner lessors alleging the existence of certain lease events of default as further described in Note 8, Debt and Capital Leases, has caused there to be substantial doubt about GenOn Mid-Atlantic's ability to continue as a going concern.

Basis of Presentation

This is a combined quarterly report of the Registrants for the quarter ended September 30, 2017. The notes to the condensed consolidated financial statements apply to the Registrants as indicated parenthetically next to each corresponding disclosure. The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the SEC's regulations for interim financial information and with the instructions to Form 10-Q. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The following notes should be read in conjunction with the accounting policies and other disclosures as set forth in the notes to the financial statements in the Registrants' 2016 Form 10-K. Interim results are not necessarily indicative of results for a full year.

In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all material adjustments consisting of normal and recurring accruals necessary to present fairly the Registrants' consolidated financial positions as of September 30, 2017, and the results of operations, comprehensive income/(loss) and cash flows for the three and nine months ended September 30, 2017 and 2016.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates.

Reclassifications

Certain prior year amounts have been reclassified for comparative purposes. The reclassifications did not affect results from operations, net assets or cash flows.