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Fair Value of Financial Instruments - Derivative Fair Value Measurements Narrative (Details) | Dec. 31, 2018
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Fair Value Disclosures [Abstract] |
Total derivative assets valued with prices provided by models and other valuation techniques percentage | 10.00%
Total derivative liabilities valued with prices provided by models and other valuation techniques, percentage | 9.00%

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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
Name: | nrg_DerivativeAssetFairValueDeterminedUsingValuationTechniquesPercentage
Namespace Prefix: | nrg_
Data Type: | num: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
Name: | nrg_DerivativeLiabilityFairValueDeterminedUsingValuationTechniquesPercentage
Namespace Prefix: | nrg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration