| Cover Cover | Nov. 04, 2021 | Aug. 05, 2021 | May 07, 2020 |
| Cover [Abstract] | |||
| Document Type | 8-K | ||
| Entity Registrant Name | NRG ENERGY, INC. | ||
| Document Period End Date | Nov. 1, 2021 | ||
| Entity Central Index Key | 0001013871 | ||
| Amendment Flag | false | ||
| Entity Incorporation, State or Country Code | DE | ||
| Entity File Number | 001-15891 | ||
| Entity Tax Identification Number | 41-1724239 | ||
| Entity Address, Address Line One | 910 Louisiana Street | ||
| Entity Address, City or Town | Houston | ||
| Entity Address, State or Province | TX | ||
| Entity Address, Postal Zip Code | 77002 | ||
| City Area Code | 713 | ||
| Local Phone Number | 537-3000 | ||
| Written Communications | false | ||
| Soliciting Material | false | ||
| Pre-commencement Tender Offer | false | ||
| Pre-commencement Issuer Tender Offer | false | ||
| Title of 12(b) Security | Common Stock, par value $0.01 | ||
| Trading Symbol | NRG | ||
| Security Exchange Name | NYSE | ||
| Entity Emerging Growth Company | false |
