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Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | $ 1,928 |  | $ 3,751 |
Mark-to-market for economic hedging activities | (71) | $ 59 | 125 | $ 41
Contract amortization | (14) |  | (28) |
Operating revenues | 2,922 | 2,701 | 5,343 | 5,083
Lease revenue | 370 |  | 622 |
Derivative revenue | (66) | 71 | 138 | 39
Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (269) |  | (451) |
Contract amortization | 0 |  | 0 |
Operating revenues | (540) | (194) | (240) | (436)
Lease revenue | 0 |  | 0 |
Energy revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 673 |  | 1,292 |
Lease revenue | 272 |  | 435 |
Derivative revenue | 580 |  | 1,012 |
Energy revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (250) |  | (411) |
Lease revenue | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
Capacity revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 313 |  | 601 |
Lease revenue | 85 |  | 164 |
Derivative revenue | 39 |  | 65 |
Capacity revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (2) |  | (3) |
Lease revenue | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
Retail revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Retail revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Retail revenue | Mass customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 1,379 |  | 2,549 |
Retail revenue | Mass customers | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (1) |  | (2) |
Retail revenue | Business solutions customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 437 |  | 753 |
Retail revenue | Business solutions customers | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Total retail revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 1,816 |  | 3,302 |
Total retail revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (1) |  | (2) |
Derivative revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | 15 |  | (91) |
Derivative revenue | 638 |  | 998 |
Derivative revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | (264) |  | 220 |
Derivative revenue | (264) |  | 220 |
Other revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 119 |  | 267 |
Lease revenue | 13 |  | 23 |
Other revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (16) |  | (35) |
Lease revenue | 0 |  | 0 |
Total operating revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 2,922 |  | 5,343 |
Total operating revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | (533) |  | (231) |
Other derivative revenue |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | 4 |  | 12 |
Other derivative revenue | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | 0 |  | 0 |
Retail | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 1,811 |  | 3,292 |
Contract amortization | 0 |  | 0 |
Operating revenues | 1,817 | 1,603 | 3,298 | 2,938
Lease revenue | 6 |  | 12 |
Retail | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | (2) | (1) | (3) | (11)
Retail | Energy revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
Retail | Capacity revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
Retail | Retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Retail | Retail revenue | Mass customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 1,380 |  | 2,551 |
Retail | Retail revenue | Business solutions customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 437 |  | 753 |
Retail | Total retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 1,817 |  | 3,304 |
Retail | Derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | 0 |  | (6) |
Derivative revenue | 0 |  | (6) |
Retail | Other revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Lease revenue | 6 |  | 12 |
Retail | Total operating revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 1,817 |  | 3,298 |
Retail | Other derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | 0 |  | 0 |
Generation | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 316 |  | 747 |
Contract amortization | 4 |  | 7 |
Operating revenues | 1,218 | 882 | 1,545 | 1,848
Lease revenue | 1 |  | 2 |
Generation | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | (546) | (171) | (239) | (406)
Generation | Energy revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 652 |  | 1,241 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 580 |  | 1,012 |
Generation | Capacity revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 228 |  | 435 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 39 |  | 65 |
Generation | Retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Generation | Retail revenue | Mass customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | Retail revenue | Business solutions customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | Total retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | Derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | 274 |  | (300) |
Derivative revenue | 897 |  | 789 |
Generation | Other revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 60 |  | 162 |
Lease revenue | 1 |  | 2 |
Generation | Total operating revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 1,218 |  | 1,545 |
Generation | Other derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | 4 |  | 12 |
Generation | Gulf Coast | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 9 |  | 157 |
Contract amortization | 4 |  | 7 |
Lease revenue | 0 |  | 0 |
Generation | Gulf Coast | Energy revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 508 |  | 879 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 610 |  | 981 |
Generation | Gulf Coast | Capacity revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 68 |  | 135 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
Generation | Gulf Coast | Retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Generation | Gulf Coast | Retail revenue | Mass customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | Gulf Coast | Retail revenue | Business solutions customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | Gulf Coast | Total retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | Gulf Coast | Derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | 289 |  | (275) |
Derivative revenue | 898 |  | 710 |
Generation | Gulf Coast | Other revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 42 |  | 128 |
Lease revenue | 0 |  | 0 |
Generation | Gulf Coast | Total operating revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 911 |  | 874 |
Generation | Gulf Coast | Other derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | (1) |  | 4 |
Generation | East and West | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 307 |  | 590 |
Contract amortization | 0 |  | 0 |
Lease revenue | 1 |  | 2 |
Generation | East and West | Energy revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 144 |  | 362 |
Lease revenue | 0 |  | 0 |
Derivative revenue | (30) |  | 31 |
Generation | East and West | Capacity revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 160 |  | 300 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 39 |  | 65 |
Generation | East and West | Retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Generation | East and West | Retail revenue | Mass customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | East and West | Retail revenue | Business solutions customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | East and West | Total retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Generation | East and West | Derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | (15) |  | (25) |
Derivative revenue | (1) |  | 79 |
Generation | East and West | Other revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 18 |  | 34 |
Lease revenue | 1 |  | 2 |
Generation | East and West | Total operating revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 307 |  | 671 |
Generation | East and West | Other derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | 5 |  | 8 |
Renewables | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 12 |  | 44 |
Contract amortization | 0 |  | 0 |
Operating revenues | 113 | 119 | 199 | 213
Lease revenue | 96 |  | 160 |
Renewables | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | (9) | (3) | (17) | (4)
Renewables | Energy revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 79 |  | 156 |
Lease revenue | 90 |  | 151 |
Derivative revenue | 0 |  | 0 |
Renewables | Capacity revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Lease revenue | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
Renewables | Retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
Renewables | Retail revenue | Mass customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Renewables | Retail revenue | Business solutions customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Renewables | Total retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
Renewables | Derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | 5 |  | (5) |
Derivative revenue | 5 |  | (5) |
Renewables | Other revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 29 |  | 48 |
Lease revenue | 6 |  | 9 |
Renewables | Total operating revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 113 |  | 199 |
Renewables | Other derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | 0 |  | 0 |
NRG Yield | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 58 |  | 119 |
Contract amortization | (18) |  | (35) |
Operating revenues | 307 | 288 | 532 | 509
Lease revenue | 267 |  | 448 |
NRG Yield | Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 0 | $ 0 | 0 | $ 0
NRG Yield | Energy revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 192 |  | 306 |
Lease revenue | 182 |  | 284 |
Derivative revenue | 0 |  | 0 |
NRG Yield | Capacity revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 87 |  | 169 |
Lease revenue | 85 |  | 164 |
Derivative revenue | 0 |  | 0 |
NRG Yield | Retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers |  |  |  |
NRG Yield | Retail revenue | Mass customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
NRG Yield | Retail revenue | Business solutions customers | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
NRG Yield | Total retail revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 |  | 0 |
NRG Yield | Derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Mark-to-market for economic hedging activities | 0 |  | 0 |
Derivative revenue | 0 |  | 0 |
NRG Yield | Other revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 46 |  | 92 |
Lease revenue | 0 |  | 0 |
NRG Yield | Total operating revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating revenues | 307 |  | 532 |
NRG Yield | Other derivative revenue | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Derivative revenue | $ 0 |  | $ 0 |

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