Fair Value of Financial Instruments - Derivative Fair Value Measurements, Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($)
Fair Value Disclosures [Abstract]
Total derivative assets valued with prices provided by models and other valuation techniques (as a percent)	29.00%
Total derivative liabilities valued with prices provided by models and other valuation techniques (as a percent)	24.00%
Decrease in cost of operations	$ 2

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.

No definition available.

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