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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
Retail Revenue | Mass customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 6,254 | 5,591 |
Retail Revenue | Business Solutions customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 1,279 | 1,303 |
Total retail revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 7,533 | 6,894 |
Energy revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 1,169 | 1,496 |
Derivative revenue |  |  |  |  |  |  |  |  | 1,595 | 1,233 |
Capacity revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 700 | 825 |
Derivative revenue |  |  |  |  |  |  |  |  | 109 | 137 |
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 |  |  |  |  |  |  |  |  | 386 | 393 |
Total operating revenues |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 9,821 | 9,478 |
Other derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative revenue |  |  |  |  |  |  |  |  | 73 | 69 |
Corporate/Eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | (5) | (19) |
Revenues |  |  |  |  |  |  |  |  | (7) | (18) | (47)
Less: Lease revenue |  |  |  |  |  |  |  |  | 0 | 0 |
Corporate/Eliminations | Retail Revenue | Mass customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | (3) | (1) |
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 |  |  |  |  |  |  |  |  | (3) | (1) |
Corporate/Eliminations | Energy revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 0 | 13 |
Derivative revenue |  |  |  |  |  |  |  |  | (1) | 14 |
Corporate/Eliminations | Capacity revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 0 | 0 |
Derivative revenue |  |  |  |  |  |  |  |  | 0 | 0 |
Corporate/Eliminations | Derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Mark-to-market for economic hedging activities |  |  |  |  |  |  |  |  | (1) | (13) |
Derivative revenue |  |  |  |  |  |  |  |  | (2) | 1 |
Corporate/Eliminations | Other revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | (3) | (17) |
Corporate/Eliminations | Total operating revenues |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | (7) | (18) |
Corporate/Eliminations | Other derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative revenue |  |  |  |  |  |  |  |  | 0 | 1 |
Texas | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 5,507 | 5,304 |
Revenues |  |  |  |  |  |  |  |  | 7,069 | 6,401 | 6,318
Less: Lease revenue |  |  |  |  |  |  |  |  | 0 | 1 |
Texas | Operating Segments | Retail Revenue | Mass customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 5,027 | 4,618 |
Texas | Operating Segments | Retail Revenue | Business Solutions customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 1,205 | 1,238 |
Texas | Operating Segments | Total retail revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 6,232 | 5,856 |
Texas | Operating Segments | Energy revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 529 | 371 |
Derivative revenue |  |  |  |  |  |  |  |  | 1,459 | 1,131 |
Texas | Operating Segments | Capacity revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 0 | 0 |
Derivative revenue |  |  |  |  |  |  |  |  | 0 | 0 |
Texas | Operating Segments | Derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Mark-to-market for economic hedging activities |  |  |  |  |  |  |  |  | 47 | (77) |
Derivative revenue |  |  |  |  |  |  |  |  | 1,562 | 1,096 |
Texas | Operating Segments | Other revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 261 | 251 |
Texas | Operating Segments | Total operating revenues |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 7,069 | 6,401 |
Texas | Operating Segments | Other derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative revenue |  |  |  |  |  |  |  |  | 56 | 42 |
Texas | Corporate/Eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | (1) | (19) | (41)
East | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 2,135 | 2,160 |
Revenues |  |  |  |  |  |  |  |  | 2,319 | 2,371 | 2,009
Less: Lease revenue |  |  |  |  |  |  |  |  | 1 | 1 |
East | Operating Segments | Retail Revenue | Mass customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 1,230 | 974 |
East | Operating Segments | Retail Revenue | Business Solutions customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 74 | 65 |
East | Operating Segments | Total retail revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 1,304 | 1,039 |
East | Operating Segments | Energy revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 322 | 546 |
Derivative revenue |  |  |  |  |  |  |  |  | 98 | 90 |
East | Operating Segments | Capacity revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 664 | 746 |
Derivative revenue |  |  |  |  |  |  |  |  | 109 | 137 |
East | Operating Segments | Derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Mark-to-market for economic hedging activities |  |  |  |  |  |  |  |  | (29) | (35) |
Derivative revenue |  |  |  |  |  |  |  |  | 183 | 210 |
East | Operating Segments | Other revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 58 | 75 |
East | Operating Segments | Total operating revenues |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 2,319 | 2,371 |
East | Operating Segments | Other derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative revenue |  |  |  |  |  |  |  |  | 5 | 17 |
East | Corporate/Eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | (8) | 5 | (1)
West/Other | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 354 | 703 |
Revenues |  |  |  |  |  |  |  |  | 440 | 724 | 788
Less: Lease revenue |  |  |  |  |  |  |  |  | 19 | 19 |
West/Other | Operating Segments | Retail Revenue | Mass customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 0 | 0 |
West/Other | Operating Segments | Retail Revenue | Business Solutions customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 0 | 0 |
West/Other | Operating Segments | Total retail revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 0 | 0 |
West/Other | Operating Segments | Energy revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 318 | 566 |
Derivative revenue |  |  |  |  |  |  |  |  | 39 | (2) |
West/Other | Operating Segments | Capacity revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 36 | 79 |
Derivative revenue |  |  |  |  |  |  |  |  | 0 | 0 |
West/Other | Operating Segments | Derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Mark-to-market for economic hedging activities |  |  |  |  |  |  |  |  | 16 | (5) |
Derivative revenue |  |  |  |  |  |  |  |  | 67 | 2 |
West/Other | Operating Segments | Other revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from contract with customer |  |  |  |  |  |  |  |  | 70 | 84 |
West/Other | Operating Segments | Total operating revenues |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 440 | 724 |
West/Other | Operating Segments | Other derivative revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative revenue |  |  |  |  |  |  |  |  | 12 | 9 |
West/Other | Corporate/Eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ 2 | $ (4) | $ 4

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