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Fair Value of Financial Instruments - Derivative Fair Value Measurements, Narrative (Details)	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Total derivative assets valued with prices provided by models and other valuation techniques (as a percent)	6.00%
Total derivative liabilities valued with prices provided by models and other valuation techniques (as a percent)	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