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Revenue Recognition - Disaggregated Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									$ 7,991	$ 8,148
Mark-to-market for economic hedging activities									(20)	14	$ 206
Revenues	$ 2,195	$ 2,996	$ 2,465	$ 2,165	$ 1,992	$ 2,960	$ 2,461	$ 2,065	9,821	9,478	9,074
Less: Lease revenue									20	21
Derivative revenue									0	31	195
Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1,222	1,548
Derivative revenue									1,649	1,284
Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									607	670
Derivative revenue									108	138
Retail Revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									6,273	5,613
Retail Revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1,403	1,492
Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									7,676	7,105
Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities									33	(130)
Derivative revenue									1,810	1,309
Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									283	285
Total operating revenues
Disaggregation of Revenue [Line Items]
Revenue from contract with customer										9,478
Revenues									9,821
Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue									19	16
Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(7)	(31)
Revenues									(1,706)	(1,068)	(923)
Less: Lease revenue									0	0
Corporate/Eliminations | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(1,498)	(1,129)
Derivative revenue									(1,499)	(1,117)
Corporate/Eliminations | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1	0
Derivative revenue									1	0
Corporate/Eliminations | Retail Revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(4)	(5)
Corporate/Eliminations | Retail Revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Corporate/Eliminations | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(4)	(5)
Corporate/Eliminations | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities									(201)	79
Derivative revenue									(1,699)	(1,037)
Corporate/Eliminations | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(4)	(13)
Corporate/Eliminations | Total operating revenues
Disaggregation of Revenue [Line Items]
Revenue from contract with customer										(1,068)
Revenues									(1,706)
Corporate/Eliminations | Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue									(1)	0
Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									7,668	7,097
Revenues									7,680	7,103	6,369
Less: Lease revenue									12	13
Retail | Operating Segments | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Derivative revenue									0	0
Retail | Operating Segments | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Derivative revenue									0	0
Retail | Operating Segments | Retail Revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									6,277	5,618
Retail | Operating Segments | Retail Revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1,403	1,492
Retail | Operating Segments | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									7,680	7,110
Retail | Operating Segments | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities									0	(7)
Derivative revenue									0	(7)
Retail | Operating Segments | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Lease revenue included in other revenue										17
Retail | Operating Segments | Total operating revenues
Disaggregation of Revenue [Line Items]
Revenue from contract with customer										7,103
Revenues									7,680
Retail | Operating Segments | Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue									0	0
Retail | Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Revenues									(10)	(9)	(4)
Generation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									330	1,082
Revenues									3,847	3,443	3,615
Less: Lease revenue									8	8
Generation | Operating Segments | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									2,720	2,677
Derivative revenue									3,148	2,401
Generation | Operating Segments | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									606	670
Derivative revenue									107	138
Generation | Operating Segments | Retail Revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | Retail Revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities									234	(202)
Derivative revenue									3,509	2,353
Generation | Operating Segments | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									287	298
Generation | Operating Segments | Total operating revenues
Disaggregation of Revenue [Line Items]
Revenues									3,847	3,443
Generation | Operating Segments | Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue									20	16
Generation | Operating Segments | Texas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(870)	(664)
Less: Lease revenue									0	0
Generation | Operating Segments | Texas | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1,987	1,585
Derivative revenue									2,917	2,332
Generation | Operating Segments | Texas | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	1
Derivative revenue									0	0
Generation | Operating Segments | Texas | Retail Revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | Texas | Retail Revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | Texas | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | Texas | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities									198	(174)
Derivative revenue									3,145	2,160
Generation | Operating Segments | Texas | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									90	84
Generation | Operating Segments | Texas | Total operating revenues
Disaggregation of Revenue [Line Items]
Revenue from contract with customer										1,496
Revenues									2,275
Generation | Operating Segments | Texas | Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue									30	2
Generation | Operating Segments | East/West Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1,200	1,746
Less: Lease revenue									8	8
Generation | Operating Segments | East/West Other | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									733	1,092
Derivative revenue									231	69
Generation | Operating Segments | East/West Other | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									606	669
Derivative revenue									107	138
Generation | Operating Segments | East/West Other | Retail Revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | East/West Other | Retail Revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | East/West Other | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									0	0
Generation | Operating Segments | East/West Other | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities									36	(28)
Derivative revenue									364	193
Generation | Operating Segments | East/West Other | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									197	214
Lease revenue included in other revenue										5
Generation | Operating Segments | East/West Other | Total operating revenues
Disaggregation of Revenue [Line Items]
Revenue from contract with customer										1,947
Revenues									1,572
Generation | Operating Segments | East/West Other | Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue									(10)	14
Generation | Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Revenues									$ (1,602)	$ (1,085)	$ (877)

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Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities

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Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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