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Fair Value of Financial Instruments - Derivative Fair Value Measurements, Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Fair Value Disclosures [Abstract] |  |
Total derivative assets valued with prices provied by models and other valuation techniques (as a percent) | 4.00% |
Total derivative liabilities valued with prices provied by models and other valuation techniques (as a percent) | 7.00% |
Decrease in credit reserve | $ 2,000,000 | $ 0

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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

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- Definition Amount of increase (decrease) in allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
Name: | us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration