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Guarantees - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Guarantor Obligations
Guarantee obligation	$ 1,746	$ 2,010
Letters of credit and surety bonds
Guarantor Obligations
Guarantee obligation	$ 1,153	1,024
Letters of credit and surety bonds, maximum expiration period (in years)	1 year
Asset sales guarantee obligations
Guarantor Obligations
Guarantee obligation	$ 506	$ 698
California property tax indemnity	$ 176

X

- Definition

The estimated amount of future payments the guarantor could be required to make under guarantees, indemnities and other contingent liability obligations.

+ References

No definition available.

+ Details

Name:	nrg_GuaranteeObligationsEstimatedExposure
Namespace Prefix:	nrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

This element represents the maximum expiration period of letters of credit and surety bonds for entity is contingently obliged.

+ References

No definition available.

+ Details

Name:	nrg_GuaranteeObligationsLettersofCreditandSuretyBondsMaximumExpirationPeriod
Namespace Prefix:	nrg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_GuaranteeObligationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_GuaranteeObligationsByNatureAxis=nrg_LettersOfCreditAndSuretyBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_GuaranteeObligationsByNatureAxis=nrg_AssetSalesGuaranteeObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: