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Fair Value Measurements (Details 2) - Level 3 $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2016 USD ($) MWh $ / MWh | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | $ 1 | $ (5) | $ 25
FTRs | FES |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | (1) | (6) | 14
NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | (107) | $ (136) | $ (151)
Model | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | 1 |  |
Model | FTRs | FES |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | (1) |  |
Model | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | $ (107) |  |
Model | Minimum | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
RTO auction clearing prices (in dollars per unit) | (4.20) |  |
Model | Minimum | FTRs | FES |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
RTO auction clearing prices (in dollars per unit) | (4.20) |  |
Model | Minimum | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Power (in dollars per MWH) | MWh | 400 |  |
Power, Regional prices (in dollars per unit) | 32.60 |  |
Model | Maximum | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
RTO auction clearing prices (in dollars per unit) | 6.10 |  |
Model | Maximum | FTRs | FES |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
RTO auction clearing prices (in dollars per unit) | 5.30 |  |
Model | Maximum | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Power (in dollars per MWH) | MWh | 2,984,000 |  |
Power, Regional prices (in dollars per unit) | 33.40 |  |
Model | Weighted Average | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
RTO auction clearing prices (in dollars per unit) | 0.80 |  |
Model | Weighted Average | FTRs | FES |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
RTO auction clearing prices (in dollars per unit) | 0.60 |  |
Model | Weighted Average | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Power (in dollars per MWH) | MWh | 754,000 |  |
Power, Regional prices (in dollars per unit) | 32.80 |  |

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