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Fair Value of Financial Instruments - Derivative Fair Value Measurements, Narrative (Details) - USD ($) $ in Millions | 6 Months Ended | 9 Months Ended
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Jun. 30, 2021 | Sep. 30, 2021
Fair Value Disclosures [Abstract] |  |
Total derivative assets valued with prices provided by models and other valuation techniques (as a percent) |  | 5.00%
Total derivative liabilities valued with prices provided by models and other valuation techniques (as a percent) |  | 3.00%
Increase in operating revenue |  | $ 7
Increase within cost of operations | $ 2 |

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- Definition Credit Reserve Decrease, Increase in Operating Revenue + References No definition available. + Details
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Namespace Prefix: | nrg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition This element represents the portion of total fair value of all derivative assets, which are valued using various valuation techniques including internal models based on a fundamental analysis of the market and extrapolation of observable market data with similar characteristics. + References No definition available. + Details
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Namespace Prefix: | nrg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Derivative Liability, Fair Value Determined Using Valuation Techniques, Percentage + References No definition available. + Details
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Namespace Prefix: | nrg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Increase In Credit Reserve, Increase In Cost Of Revenue + References No definition available. + Details
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Namespace Prefix: | nrg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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Balance Type: | na
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