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Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations
Under 1 Year	$ 1,467
1-3 Years	98
3-5 Years	264
Over 5 Years	761
Guarantees by Remaining Maturity, Total	2,590	$ 2,767
Letters of credit and surety bonds
Guarantor Obligations
Under 1 Year	1,467
1-3 Years	66
3-5 Years	7
Over 5 Years	93
Guarantees by Remaining Maturity, Total	$ 1,633	1,837
Letters of credit and surety bonds, maximum expiration period (in years)	1 year
Asset sales guarantee obligations
Guarantor Obligations
Under 1 Year	$ 0
1-3 Years	0
3-5 Years	257
Over 5 Years	55
Guarantees by Remaining Maturity, Total	312	677
Other guarantees
Guarantor Obligations
Under 1 Year	0
1-3 Years	32
3-5 Years	0
Over 5 Years	613
Guarantees by Remaining Maturity, Total	645	253
Eliminations | Letters of credit and surety bonds
Guarantor Obligations
Guarantees by Remaining Maturity, Total	$ 92	$ 272

X

- Definition

Maximum potential amount of future payments that the guarantor could be required to make between one to three years of the balance sheet date under the guarantee.

+ References

No definition available.

+ Details

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

X

- Definition

Maximum potential amount of future payments that the guarantor could be required to make between three to five years of the balance sheet date under the guarantee.

+ References

No definition available.

+ Details

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

X

- Definition

Maximum potential amount of future payments that the guarantor could be required to make after five years of the balance sheet date under the guarantee.

+ References

No definition available.

+ Details

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

X

- Definition

Maximum potential amount of future payments that the guarantor could be required to make within one year of the balance sheet date under the guarantee.

+ References

No definition available.

+ Details

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

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

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:

X

- Details

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

X

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_ConsolidationEliminationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: