Summary of Significant Accounting Policies - Noncontrolling Interest (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Noncontrolling Interest [Roll Forward]
Balance as of beginning of period	$ 2,314
Dividends paid to NRG Yield, Inc. public shareholders	(30)
Distributions to noncontrolling interest	(19)
Comprehensive income (loss) attributable to noncontrolling interest	(38)	$ (39)
Contributions from noncontrolling interest	147
Sale of assets to NRG Yield, Inc.	(4)
Balance as of end of period	2,392
Noncontrolling Interest
Noncontrolling Interest [Roll Forward]
Comprehensive income (loss) attributable to noncontrolling interest	(22)
Non-cash adjustments to noncontrolling interest	$ 6

Noncontrolling interest, Contributions from Noncontrolling Interests

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Noncontrolling Interest, Decrease From Dividend Distribution

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Noncontrolling Interest, Noncash Adjustments

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

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Decrease in noncontrolling interest balance from payment of dividends or other distributions by the non-wholly owned subsidiary or partially owned entity, included in the consolidation of the parent entity, to the noncontrolling interest holders.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of increase in noncontrolling interest from sale of a portion of the parent's controlling interest.

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