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Accounting for Derivative Instruments and Hedging Activities - Effect on Accumulated OCI Balance Attributable to Cash Flow Hedge Derivatives, Net (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income [Roll Forward]
Beginning balance	$ 1,968
Sale of NRG Yield and Renewables	25
Ending balance	(1,234)
Interest rate contracts | AOCI Including Portion Attributable to Noncontrolling Interest
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income [Roll Forward]
Beginning balance	(54)
Ending balance	0
Interest rate contracts | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income [Roll Forward]
Due to realization of previously deferred amounts	8
Interest rate contracts | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income [Roll Forward]
Mark-to-market of cash flow hedge accounting contracts	$ 21

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Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income

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Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI, Divestiture Of Business, Net of Tax

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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount, after tax and adjustments, of gain (loss) from increase (decrease) in value of excluded component of derivative designated and qualifying as hedge. Adjustments include, but are not limited to, reclassifications for sale and settlement, and amounts recognized under systematic and rational method.

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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