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Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,779	$ 1,804
Mark-to-market for economic hedging activities	20	206
Operating revenues	2,165	2,065
Lease revenue	5	5
Derivative revenue	27	214
Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	306	443
Derivative revenue	336	316
Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	154	142
Derivative revenue	18	26
Retail revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,320	1,175
Retail revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	286	310
Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,606	1,485
Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	20	(96)
Derivative revenue	381	256
Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	79	91
Total operating revenue
Disaggregation of Revenue [Line Items]
Operating revenues	2,165	2,065
Other revenue, derivative
Disaggregation of Revenue [Line Items]
Derivative revenue	7	8
Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(3)	(12)
Operating revenues	(266)	314
Lease revenue	0	0
Corporate/Eliminations | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(276)	(161)
Derivative revenue	(277)	(157)
Corporate/Eliminations | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)	0
Derivative revenue	0	0
Corporate/Eliminations | Retail revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)	(1)
Corporate/Eliminations | Retail revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Corporate/Eliminations | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)	(1)
Corporate/Eliminations | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	15	484
Derivative revenue	(262)	327
Corporate/Eliminations | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(2)	(7)
Corporate/Eliminations | Total operating revenue
Disaggregation of Revenue [Line Items]
Operating revenues	(265)	315
Corporate/Eliminations | Other revenue, derivative
Disaggregation of Revenue [Line Items]
Derivative revenue	0	0
Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,604	1,483
Operating revenues	1,607	1,480
Lease revenue	3	3
Retail | Operating Segments | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Derivative revenue	0	0
Retail | Operating Segments | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Derivative revenue	0	0
Retail | Operating Segments | Retail revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,321	1,176
Retail | Operating Segments | Retail revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	286	310
Retail | Operating Segments | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,607	1,486
Retail | Operating Segments | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	0	(6)
Derivative revenue	0	(6)
Retail | Operating Segments | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Retail | Operating Segments | Total operating revenue
Disaggregation of Revenue [Line Items]
Operating revenues	1,607	1,480
Retail | Operating Segments | Other revenue, derivative
Disaggregation of Revenue [Line Items]
Derivative revenue	0	0
Retail | Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(3)	(1)
Generation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	178	333
Operating revenues	823	270
Lease revenue	2	2
Generation | Operating Segments | Texas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(146)	(101)
Lease revenue	0	0
Generation | Operating Segments | East/West/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	324	434
Lease revenue	2	2
Generation | Operating Segments | Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	582	604
Derivative revenue	613	473
Generation | Operating Segments | Energy revenue | Texas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	358	265
Derivative revenue	525	413
Generation | Operating Segments | Energy revenue | East/West/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	224	339
Derivative revenue	88	60
Generation | Operating Segments | Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	155	142
Derivative revenue	18	26
Generation | Operating Segments | Capacity revenue | Texas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Derivative revenue	0	0
Generation | Operating Segments | Capacity revenue | East/West/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	155	142
Derivative revenue	18	26
Generation | Operating Segments | Retail revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Retail revenue | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Retail revenue | Texas | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Retail revenue | Texas | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Retail revenue | East/West/Other | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Retail revenue | East/West/Other | Business Solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Total retail revenue | Texas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Total retail revenue | East/West/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Generation | Operating Segments | Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	5	(574)
Derivative revenue	643	(65)
Generation | Operating Segments | Derivative revenue | Texas
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	13	(569)
Derivative revenue	546	(150)
Generation | Operating Segments | Derivative revenue | East/West/Other
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	(8)	(5)
Derivative revenue	97	85
Generation | Operating Segments | Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	81	98
Generation | Operating Segments | Other revenue | Texas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	29	53
Generation | Operating Segments | Other revenue | East/West/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	52	45
Generation | Operating Segments | Total operating revenue
Disaggregation of Revenue [Line Items]
Operating revenues	823	270
Generation | Operating Segments | Total operating revenue | Texas
Disaggregation of Revenue [Line Items]
Operating revenues	400	(251)
Generation | Operating Segments | Total operating revenue | East/West/Other
Disaggregation of Revenue [Line Items]
Operating revenues	423	521
Generation | Operating Segments | Other revenue, derivative
Disaggregation of Revenue [Line Items]
Derivative revenue	7	8
Generation | Operating Segments | Other revenue, derivative | Texas
Disaggregation of Revenue [Line Items]
Derivative revenue	8	5
Generation | Operating Segments | Other revenue, derivative | East/West/Other
Disaggregation of Revenue [Line Items]
Derivative revenue	(1)	3
Generation | Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	$ (235)	$ 309

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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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