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Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | $ 1,823 |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | 196 | $ (19)
Derivative revenue | 204 | (33)
Contract amortization | (14) |
Operating revenues | 2,421 | 2,382
Lease revenue | 252 |
Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | (182) |
Contract amortization | 0 |
Operating revenues | 300 | (244)
Lease revenue | 0 |
Energy revenue |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 619 |
Derivative revenue | 432 |
Lease revenue | 163 |
Energy revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | (161) |
Derivative revenue | 0 |
Lease revenue | 0 |
Capacity revenue |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 288 |
Derivative revenue | 26 |
Lease revenue | 79 |
Capacity revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | (1) |
Derivative revenue | 0 |
Lease revenue | 0 |
Retail |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Retail | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Retail | Mass customers |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 1,170 |
Retail | Mass customers | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | (1) |
Retail | Business solutions customers |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 316 |
Retail | Business solutions customers | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Total retail revenue |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 1,486 |
Total retail revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | (1) |
Derivative revenue |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | (106) |
Derivative revenue | 360 |
Derivative revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | 484 |
Derivative revenue | 484 |
Other revenue |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 148 |
Lease revenue | 10 |
Other revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | (19) |
Lease revenue | 0 |
Total operating revenue |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 2,421 |
Total operating revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 302 |
Other derivative revenue |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 8 |
Other derivative revenue | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 0 |
Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 1,481 |
Contract amortization | 0 |
Operating revenues | 1,481 | 1,335
Lease revenue | 6 |
Retail | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | (1) | (1)
Retail | Energy revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Derivative revenue | 0 |
Lease revenue | 0 |
Retail | Capacity revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Derivative revenue | 0 |
Lease revenue | 0 |
Retail | Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Retail | Retail | Mass customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 1,171 |
Retail | Retail | Business solutions customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 316 |
Retail | Total retail revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 1,487 |
Retail | Derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | (6) |
Derivative revenue | (6) |
Retail | Other revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Lease revenue | 6 |
Retail | Total operating revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 1,481 |
Retail | Other derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 0 |
Generation | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 431 |
Contract amortization | 3 |
Operating revenues | 327 | 965
Lease revenue | 1 |
Generation | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 307 | (209)
Generation | Energy revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 589 |
Derivative revenue | 432 |
Lease revenue | 0 |
Generation | Capacity revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 207 |
Derivative revenue | 26 |
Lease revenue | 0 |
Generation | Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Generation | Retail | Mass customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | Retail | Business solutions customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | Total retail revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | Derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | (574) |
Derivative revenue | (108) |
Generation | Other revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 102 |
Lease revenue | 1 |
Generation | Total operating revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 327 |
Generation | Other derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 8 |
Generation | Gulf Coast | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 148 |
Contract amortization | 3 |
Lease revenue | 0 |
Generation | Gulf Coast | Energy revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 371 |
Derivative revenue | 371 |
Lease revenue | 0 |
Generation | Gulf Coast | Capacity revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 67 |
Derivative revenue | 0 |
Lease revenue | 0 |
Generation | Gulf Coast | Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Generation | Gulf Coast | Retail | Mass customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | Gulf Coast | Retail | Business solutions customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | Gulf Coast | Total retail revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | Gulf Coast | Derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | (564) |
Derivative revenue | (188) |
Generation | Gulf Coast | Other revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 86 |
Lease revenue | 0 |
Generation | Gulf Coast | Total operating revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | (37) |
Generation | Gulf Coast | Other derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 5 |
Generation | East and West | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 283 |
Contract amortization | 0 |
Lease revenue | 1 |
Generation | East and West | Energy revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 218 |
Derivative revenue | 61 |
Lease revenue | 0 |
Generation | East and West | Capacity revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 140 |
Derivative revenue | 26 |
Lease revenue | 0 |
Generation | East and West | Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Generation | East and West | Retail | Mass customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | East and West | Retail | Business solutions customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | East and West | Total retail revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Generation | East and West | Derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | (10) |
Derivative revenue | 80 |
Generation | East and West | Other revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 16 |
Lease revenue | 1 |
Generation | East and West | Total operating revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 364 |
Generation | East and West | Other derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 3 |
Renewables | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 32 |
Contract amortization | 0 |
Operating revenues | 86 | 95
Lease revenue | 64 |
Renewables | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | (8) | (8)
Renewables | Energy revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 77 |
Derivative revenue | 0 |
Lease revenue | 61 |
Renewables | Capacity revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Derivative revenue | 0 |
Lease revenue | 0 |
Renewables | Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
Renewables | Retail | Mass customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Renewables | Retail | Business solutions customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Renewables | Total retail revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
Renewables | Derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | (10) |
Derivative revenue | (10) |
Renewables | Other revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 19 |
Lease revenue | 3 |
Renewables | Total operating revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 86 |
Renewables | Other derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | 0 |
NRG Yield | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 61 |
Contract amortization | (17) |
Operating revenues | 225 | 221
Lease revenue | 181 |
NRG Yield | Eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 0 | $ 0
NRG Yield | Energy revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 114 |
Derivative revenue | 0 |
Lease revenue | 102 |
NRG Yield | Capacity revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 82 |
Derivative revenue | 0 |
Lease revenue | 79 |
NRG Yield | Retail | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers |  |
NRG Yield | Retail | Mass customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
NRG Yield | Retail | Business solutions customers | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
NRG Yield | Total retail revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 0 |
NRG Yield | Derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities | 0 |
Derivative revenue | 0 |
NRG Yield | Other revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Revenue from contracts with customers | 46 |
Lease revenue | 0 |
NRG Yield | Total operating revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues | 225 |
NRG Yield | Other derivative revenue | Operating Segments |  |
Disaggregation of Revenue [Line Items] |  |
Derivative revenue | $ 0 |

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