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Fair Value of Financial Instruments - Derivative Fair Value Measurements, Narrative (Details) $ in Millions | 9 Months Ended
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Sep. 30, 2019 USD ($)
Fair Value Disclosures [Abstract] |
Total derivative assets valued with prices provided by models and other valuation techniques (as a percent) | 11.00%
Total derivative liabilities valued with prices provided by models and other valuation techniques (as a percent) | 11.00%
Decrease in cost of operations | $ 1

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- Definition Decrease In Credit Reserve, Decrease In Cost Of Revenue + References No definition available. + Details
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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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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: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
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