Regulatory Matters	12 Months Ended
Dec. 31, 2018
Regulatory Matters Disclosure [Abstract]
Regulatory Matters	Regulatory Matters NRG operates in a highly regulated industry and is subject to regulation by various federal and state agencies. As such, NRG is affected by regulatory developments at both the federal and state levels and in the regions in which NRG operates. In addition, NRG is subject to the market rules, procedures, and protocols of the various ISO and RTO markets in which NRG participates. These power markets are subject to ongoing legislative and regulatory changes that may impact NRG's wholesale and retail businesses. In addition to the regulatory proceedings noted below, NRG and its subsidiaries are parties to other regulatory proceedings arising in the ordinary course of business or have other regulatory exposure. In management's opinion, the disposition of these ordinary course matters will not materially adversely affect NRG's consolidated financial position, results of operations, or cash flows. Zero-Emission Credits for Nuclear Plants in Illinois and New York - In 2016, Illinois enacted a Zero Emission Credit, or ZEC, program for selected nuclear units in Illinois. In total, the program directs over $2.5 billion over ten years to two Exelon-owned nuclear power plants in Illinois. That same year, the NYSPSC issued its Clean Energy Standard, or CES, which provides for ZECs which would provide more than $7.6 billion over 12 years in out-of-market subsidy payments to certain selected nuclear generating units in New York. These ZECs are out-of-market subsidies that threaten to artificially suppress market prices and interfere with the wholesale power market. NRG, along with other companies, filed complaints in the federal courts of Illinois and New York alleging that these state programs are preempted by federal law and in violation of the dormant commerce clause. These cases have proceeded through the federal district court as well as the federal appellate court in Illinois and New York, respectively. On January 7, 2019, NRG and its trade association filed a Petition for Writ of Certiorari with the United States Supreme Court in both cases. California Station Power - As the result of unfavorable final and non-appealable litigation, the Company has accrued a liability associated with consumption of station power at three of the Company’s power plants in California, after August 30, 2010. In December 2017, subsidiaries of the Company entered into settlements with SCE for the liabilities associated with the Company's El Segundo and Long Beach facilities. The Company has established an appropriate reserve pending potential regulatory action by SDG&E regarding Encina. South Central - On August 4, 2016, NRG received a document hold notice from FERC regarding conduct in the MISO and PJM markets. It required NRG to retain communications related to multiple generating units in the South Central region. Since sending the notice, FERC has been investigating potential violations of MISO rules involving bidding for the Big Cajun 2 facility, as well as other aspects of NRG’s operations in MISO. FERC has the authority to require disgorgement of profits and to impose penalties and NRG retains any liability following the sale of the South Central Portfolio. We expect a preliminary finding from FERC by the second quarter of 2019. ISO-NE - On February 5, 2019, FERC has informed the Company that it has made a preliminary finding that the Company violated FERC's market behavior rules in connection with offers made into the ISO-NE Forward Capacity Auction in 2016. The Company understands that FERC is concerned that the Company was inaccurate in its communications with the Market Monitor regarding the costs and risks associated with operating certain units in the forward timeframe. Ultimately, the Company opted to withdraw the relevant bids prior to the auction in 2016. The Company will be engaging in discussions with FERC regarding this matter.

Regulatory Matters

NRG operates in a highly regulated industry and is subject to regulation by various federal and state agencies. As such, NRG is affected by regulatory developments at both the federal and state levels and in the regions in which NRG operates. In addition, NRG is subject to the market rules, procedures, and protocols of the various ISO and RTO markets in which NRG participates. These power markets are subject to ongoing legislative and regulatory changes that may impact NRG's wholesale and retail businesses.

In addition to the regulatory proceedings noted below, NRG and its subsidiaries are parties to other regulatory proceedings arising in the ordinary course of business or have other regulatory exposure. In management's opinion, the disposition of these ordinary course matters will not materially adversely affect NRG's consolidated financial position, results of operations, or cash flows.

Zero-Emission Credits for Nuclear Plants in Illinois and New York - In 2016, Illinois enacted a Zero Emission Credit, or ZEC, program for selected nuclear units in Illinois. In total, the program directs over $2.5 billion over ten years to two Exelon-owned nuclear power plants in Illinois. That same year, the NYSPSC issued its Clean Energy Standard, or CES, which provides for ZECs which would provide more than $7.6 billion over 12 years in out-of-market subsidy payments to certain selected nuclear generating units in New York. These ZECs are out-of-market subsidies that threaten to artificially suppress market prices and interfere with the wholesale power market. NRG, along with other companies, filed complaints in the federal courts of Illinois and New York alleging that these state programs are preempted by federal law and in violation of the dormant commerce clause. These cases have proceeded through the federal district court as well as the federal appellate court in Illinois and New York, respectively. On January 7, 2019, NRG and its trade association filed a Petition for Writ of Certiorari with the United States Supreme Court in both cases.

California Station Power - As the result of unfavorable final and non-appealable litigation, the Company has accrued a liability associated with consumption of station power at three of the Company’s power plants in California, after August 30, 2010. In December 2017, subsidiaries of the Company entered into settlements with SCE for the liabilities associated with the Company's El Segundo and Long Beach facilities. The Company has established an appropriate reserve pending potential regulatory action by SDG&E regarding Encina.

South Central - On August 4, 2016, NRG received a document hold notice from FERC regarding conduct in the MISO and PJM markets. It required NRG to retain communications related to multiple generating units in the South Central region. Since sending the notice, FERC has been investigating potential violations of MISO rules involving bidding for the Big Cajun 2 facility, as well as other aspects of NRG’s operations in MISO. FERC has the authority to require disgorgement of profits and to impose penalties and NRG retains any liability following the sale of the South Central Portfolio. We expect a preliminary finding from FERC by the second quarter of 2019.

ISO-NE - On February 5, 2019, FERC has informed the Company that it has made a preliminary finding that the Company violated FERC's market behavior rules in connection with offers made into the ISO-NE Forward Capacity Auction in 2016. The Company understands that FERC is concerned that the Company was inaccurate in its communications with the Market Monitor regarding the costs and risks associated with operating certain units in the forward timeframe. Ultimately, the Company opted to withdraw the relevant bids prior to the auction in 2016. The Company will be engaging in discussions with FERC regarding this matter.