Impairments (GenOn)	9 Months Ended
Sep. 30, 2017
Asset Impairment Charges [Abstract]
Impairments (GenOn)	Impairments (GenOn) 2016 Long-Lived Asset Impairments (GenOn) Mandalay and Ormond Beach (GenOn) — On May 26, 2016, the CPUC rejected a multi-year resource adequacy contract between Mandalay and Southern California Edison. Also occurring during the second quarter of 2016, the Statewide Advisory Committee on Cooling Water Intake Structures, or SACCWIS, issued a draft April 2016 Report noting that CAISO plans to continue to assume in its transmission studies that Ormond Beach will not operate after December 31, 2020, the deadline for Ormond Beach compliance with California regulations to mitigate once-through cooling (OTC) impacts. GenOn does not anticipate that contracts of sufficient value can be secured to support the significant investment required to design, permit, construct and operate measures required for OTC compliance. As a result, on May 6, 2016, GenOn notified SACCWIS that it does not expect to continue to operate Ormond Beach beyond 2020. Additionally, during the second quarter of 2016, CAISO issued its Local Capacity Requirements report for 2017 indicating unfavorable changes within the local reliability areas in which both Mandalay and Ormond Beach are located. The culmination of these events were considered to be indicators of impairment and as a result, GenOn performed impairment tests for the Mandalay and Ormond Beach assets under ASC 360, Property, Plant and Equipment. Based on the results of the impairment tests, GenOn determined that the carrying amount of these assets was higher than the estimated future net cash flows expected to be generated by the respective assets and that the Mandalay and Ormond Beach assets were impaired. The fair value of the Mandalay and Ormond Beach operating units was determined using the income approach which utilizes estimates of discounted future cash flows, which were Level 3 fair value measurements and include key inputs such as forecasted contract prices, forecasted operating expenses and discount rates. GenOn measured the impairment losses as the difference between the carrying amount of the Mandalay and Ormond Beach operating units and the present value of the estimated future net cash flows for each respective operating unit. GenOn recorded an impairment loss of $16 million and $43 million for Mandalay and Ormond Beach, respectively, during the quarter ended June 30, 2016.

Impairments (GenOn)

2016 Long-Lived Asset Impairments (GenOn)

Mandalay and Ormond Beach (GenOn) — On May 26, 2016, the CPUC rejected a multi-year resource adequacy contract between Mandalay and Southern California Edison. Also occurring during the second quarter of 2016, the Statewide Advisory Committee on Cooling Water Intake Structures, or SACCWIS, issued a draft April 2016 Report noting that CAISO plans to continue to assume in its transmission studies that Ormond Beach will not operate after December 31, 2020, the deadline for Ormond Beach compliance with California regulations to mitigate once-through cooling (OTC) impacts. GenOn does not anticipate that contracts of sufficient value can be secured to support the significant investment required to design, permit, construct and operate measures required for OTC compliance. As a result, on May 6, 2016, GenOn notified SACCWIS that it does not expect to continue to operate Ormond Beach beyond 2020. Additionally, during the second quarter of 2016, CAISO issued its Local Capacity Requirements report for 2017 indicating unfavorable changes within the local reliability areas in which both Mandalay and Ormond Beach are located. The culmination of these events were considered to be indicators of impairment and as a result, GenOn performed impairment tests for the Mandalay and Ormond Beach assets under ASC 360, Property, Plant and Equipment. Based on the results of the impairment tests, GenOn determined that the carrying amount of these assets was higher than the estimated future net cash flows expected to be generated by the respective assets and that the Mandalay and Ormond Beach assets were impaired. The fair value of the Mandalay and Ormond Beach operating units was determined using the income approach which utilizes estimates of discounted future cash flows, which were Level 3 fair value measurements and include key inputs such as forecasted contract prices, forecasted operating expenses and discount rates. GenOn measured the impairment losses as the difference between the carrying amount of the Mandalay and Ormond Beach operating units and the present value of the estimated future net cash flows for each respective operating unit. GenOn recorded an impairment loss of $16 million and $43 million for Mandalay and Ormond Beach, respectively, during the quarter ended June 30, 2016.