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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

X

- 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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X

- 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

X

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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X

- 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

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