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Nature of Business and Basis of Presentation - General (Details) counterparty in Millions	9 Months Ended
	Sep. 30, 2021 counterparty MW
Business Acquisition [Line Items]
Generation capacity (in MW)	23,000
East
Business Acquisition [Line Items]
Generation capacity (in MW)	1,600
Disposal Group, Held-for-sale, Not Discontinued Operations
Business Acquisition [Line Items]
Generation capacity (in MW)	4,850
Home
Business Acquisition [Line Items]
Customers | counterparty	6

X

- Definition

Number of customers

+ References

No definition available.

+ Details

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Namespace Prefix:	nrg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The generation capacity of the entity's power generation facilities as of the balance sheet date, expressed in megawatts.

+ References

No definition available.

+ Details

Name:	nrg_PowerGenerationCapacityMegawatts
Namespace Prefix:	nrg_
Data Type:	dtr-types:powerItemType
Balance Type:	na
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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Period Type:	duration

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=nrg_EastSegmentMember
Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_MajorCustomersAxis=nrg_HomeCustomerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: