Dispositions (Notes)	3 Months Ended
Mar. 31, 2017
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions Disclosures [Text Block]	Dispositions (GenOn and GenOn Americas Generation) 2017 Dispositions Sale of Emission Allowances (GenOn and GenOn Americas Generation) During the three months ended March 31, 2017, GenOn Energy Management, through its existing agreement with NRG Power Marketing, LLC, sold 1.3 million of certain emission credit allowances for proceeds of $18 million resulting in a gain on the sale of approximately $1 million. 2016 Dispositions Potrero Disposition (GenOn and GenOn Americas Generation) On September 26, 2016, NRG Potrero LLC, or Potrero, an indirect wholly owned subsidiary of GenOn Americas Generation, completed the sale of real property at the Potrero generating station located in San Francisco, CA to California Barrel Company, LLC for total consideration of $86 million comprised of $74 million of cash received, which is net of $8 million of closing costs and $4 million to be held in escrow in order to cover post closing obligations. The sale resulted in a gain of approximately $74 million recognized within GenOn Americas Generation's consolidated results of operations during the third quarter of 2016. Aurora Disposition (GenOn) On May 12, 2016, GenOn entered into an agreement with RA Generation, LLC to sell the Aurora Generating Station, or Aurora, for cash consideration of $365 million, subject to adjustments for working capital and the results of the PJM 2019/2020 Base Residual Auction. Aurora is an 878 MW natural gas facility located in Aurora, Illinois. On July 12, 2016, GenOn completed the sale of Aurora for cash proceeds of $369 million, including $4 million in adjustments primarily for the PJM base residual auction results and estimated working capital, which is subject to further adjustment. The sale resulted in a gain of approximately $188 million recognized within GenOn's consolidated results of operations during the quarter ended September 30, 2016. In connection with the sale, GenOn issued a guaranty to RA Generation, LLC for the payment of certain indemnified costs related to any damages, losses, or other expenses arising out of misrepresentation or breach of warranties or covenants under the purchase agreement subject to a cap of $365 million, which is reduced to $183 million on January 1, 2018 and then to $91 million beginning January 1, 2019 and will terminate upon the third anniversary of the sale. Seward Disposition (GenOn) On November 24, 2015, GenOn entered into an agreement with Seward Generation, LLC and an affiliate of Robindale Energy Services, Inc. to sell the Seward Generating Station, a 525 MW coal-fired facility in Pennsylvania, for cash consideration of $75 million. On February 2, 2016, GenOn completed the sale of Seward and received gross cash proceeds of $75 million excluding $3 million of cash on hand transferred to the buyer. GenOn will also receive $5 million in deferred cash consideration in five $1 million annual installments and up to $2.5 million in payments contingent upon certain environmental requirements being imposed by August 2017. In addition, Robindale committed to future inventory purchases from GenOn of $13 million through 2019. Shelby Disposition (GenOn) On November 9, 2015, GenOn entered into an agreement with an affiliate of Rockland Power Partners II, LP and Shelby County Energy Center, LLC to sell the Shelby Generating Station, a 352 MW natural gas-fired facility located in Illinois for cash consideration of $46 million. At December 31, 2015, GenOn had classified on its balance sheet the assets and liabilities of Shelby as held for sale. On March 1, 2016, GenOn completed the sale of Shelby for cash proceeds of $46 million which resulted in a gain of $29 million recognized within GenOn's consolidated results of operations during the first quarter of 2016. In addition, GenOn retained $10 million related to future revenue rights as part of the agreement of which $9 million had been collected as of March 31, 2017.

Dispositions (GenOn and GenOn Americas Generation)

2017 Dispositions

Sale of Emission Allowances (GenOn and GenOn Americas Generation)

During the three months ended March 31, 2017, GenOn Energy Management, through its existing agreement with NRG Power Marketing, LLC, sold 1.3 million of certain emission credit allowances for proceeds of $18 million resulting in a gain on the sale of approximately $1 million.

2016 Dispositions

Potrero Disposition (GenOn and GenOn Americas Generation)

On September 26, 2016, NRG Potrero LLC, or Potrero, an indirect wholly owned subsidiary of GenOn Americas Generation, completed the sale of real property at the Potrero generating station located in San Francisco, CA to California Barrel Company, LLC for total consideration of $86 million comprised of $74 million of cash received, which is net of $8 million of closing costs and $4 million to be held in escrow in order to cover post closing obligations. The sale resulted in a gain of approximately $74 million recognized within GenOn Americas Generation's consolidated results of operations during the third quarter of 2016.

Aurora Disposition (GenOn)

On May 12, 2016, GenOn entered into an agreement with RA Generation, LLC to sell the Aurora Generating Station, or Aurora, for cash consideration of $365 million, subject to adjustments for working capital and the results of the PJM 2019/2020 Base Residual Auction. Aurora is an 878 MW natural gas facility located in Aurora, Illinois. On July 12, 2016, GenOn completed the sale of Aurora for cash proceeds of $369 million, including $4 million in adjustments primarily for the PJM base residual auction results and estimated working capital, which is subject to further adjustment. The sale resulted in a gain of approximately $188 million recognized within GenOn's consolidated results of operations during the quarter ended September 30, 2016. In connection with the sale, GenOn issued a guaranty to RA Generation, LLC for the payment of certain indemnified costs related to any damages, losses, or other expenses arising out of misrepresentation or breach of warranties or covenants under the purchase agreement subject to a cap of $365 million, which is reduced to $183 million on January 1, 2018 and then to $91 million beginning January 1, 2019 and will terminate upon the third anniversary of the sale.

Seward Disposition (GenOn)

On November 24, 2015, GenOn entered into an agreement with Seward Generation, LLC and an affiliate of Robindale Energy Services, Inc. to sell the Seward Generating Station, a 525 MW coal-fired facility in Pennsylvania, for cash consideration of $75 million. On February 2, 2016, GenOn completed the sale of Seward and received gross cash proceeds of $75 million excluding $3 million of cash on hand transferred to the buyer. GenOn will also receive $5 million in deferred cash consideration in five $1 million annual installments and up to $2.5 million in payments contingent upon certain environmental requirements being imposed by August 2017. In addition, Robindale committed to future inventory purchases from GenOn of $13 million through 2019.

Shelby Disposition (GenOn)

On November 9, 2015, GenOn entered into an agreement with an affiliate of Rockland Power Partners II, LP and Shelby County Energy Center, LLC to sell the Shelby Generating Station, a 352 MW natural gas-fired facility located in Illinois for cash consideration of $46 million. At December 31, 2015, GenOn had classified on its balance sheet the assets and liabilities of Shelby as held for sale. On March 1, 2016, GenOn completed the sale of Shelby for cash proceeds of $46 million which resulted in a gain of $29 million recognized within GenOn's consolidated results of operations during the first quarter of 2016. In addition, GenOn retained $10 million related to future revenue rights as part of the agreement of which $9 million had been collected as of March 31, 2017.