Summary of Significant Accounting Policies - Redeemable Non Controlling Interest (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Roll Forward]
Balance at beginning of period	$ 20	$ 19	$ 78
Distributions to redeemable noncontrolling interest			(43)
Contributions from redeemable noncontrolling interest			26
Net income attributable to redeemable noncontrolling interest - continuing operations		3	1
Net loss attributable to redeemable noncontrolling interest - discontinued operations			(27)
Sale of NRG Yield and the Renewables Platform			(2,548)
Repurchase of redeemable noncontrolling interest	(20)
Balance at end of period	$ 0	20	19
NRG Yield Inc. And Zephyr Renewables
Noncontrolling Interest [Roll Forward]
Sale of NRG Yield and the Renewables Platform			(48)
Redeemable noncontrolling interest
Noncontrolling Interest [Roll Forward]
Distributions to redeemable noncontrolling interest		$ (2)	(3)
Non-cash adjustments to redeemable noncontrolling interest			$ (8)

Noncontrolling Interest, Noncash Adjustments

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Noncontrolling Interest

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Redeemable Noncontrolling Interest, Cash Contributions from Noncontrolling Interest Holders

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Amount after tax of income (loss) from a discontinued operation attributable to the noncontrolling interest. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

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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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Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

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Amount of Net Income (Loss) attributable to redeemable noncontrolling interest.

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The amount of the reduction or elimination during the period of a noncontrolling interest resulting from the parent's loss of control and deconsolidation of the entity in which one or more outside parties had a noncontrolling interest.

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Amount of noncontrolling interests which are redeemable by the parent entity, classified as other equity.

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