Summary of Significant Accounting Policies - Redeemable Noncontrolling Interest (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Noncontrolling Interest [Line Items]
Balance as of beginning of period	$ 78
Distributions to noncontrolling interest	(43)
Contributions from redeemable noncontrolling interest	26
Net income attributable to redeemable noncontrolling interest - continuing operations	5
Net income attributable to redeemable noncontrolling interest - discontinued operations	21
Balance as of end of period	19
Redeemable Noncontrolling Interest
Noncontrolling Interest [Line Items]
Distributions to noncontrolling interest	(3)
Non-cash adjustments to noncontrolling interest	(9)
Net income attributable to redeemable noncontrolling interest - continuing operations	1
Net income attributable to redeemable noncontrolling interest - discontinued operations	(26)
NRG Yield and Renewables
Noncontrolling Interest [Line Items]
Deconsolidation of NRG Yield and Renewables Platform	(2,180)
NRG Yield and Renewables \| Redeemable Noncontrolling Interest
Noncontrolling Interest [Line Items]
Deconsolidation of NRG Yield and Renewables Platform	$ (48)

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