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Goodwill and Other Intangibles - Out of Market Contracts (Details) - Out of Market Contracts $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Out of Market Contracts Five Year Maturity
2018	$ 25
2019	25
2020	26
2021	23
2022	10
Power Contracts
Out of Market Contracts Five Year Maturity
2018	16
2019	16
2020	17
2021	14
2022	1
Lease Agreements
Out of Market Contracts Five Year Maturity
2018	9
2019	9
2020	9
2021	9
2022	$ 9

X

- Definition

The amount of amortization for out-of-market contracts expected to be recognized during the fifth twelve-month period following the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	nrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The amount of amortization for out-of-market contracts expected to be recognized during the fourth twelve-month period following the balance sheet date.

+ References

No definition available.

+ Details

Name:	nrg_FutureAmortizationExpensesOutOfMarketContractsYearFour
Namespace Prefix:	nrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The amount of amortization for out-of-market contracts expected to be recognized during the twelve-month period following the balance sheet date.

+ References

No definition available.

+ Details

Name:	nrg_FutureAmortizationExpensesOutOfMarketContractsYearOne
Namespace Prefix:	nrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The amount of amortization for out-of-market contracts expected to be recognized during the third twelve-month period following the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	nrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The amount of amortization for out-of-market contracts expected to be recognized during the second twelve-month period following the balance sheet date.

+ References

No definition available.

+ Details

Name:	nrg_FutureAmortizationExpensesOutOfMarketContractsYearTwo
Namespace Prefix:	nrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Out of Market Contract Five Year Maturity

+ References

No definition available.

+ Details

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- Details

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X

- Details

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- Details

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