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v3.19.1

Fair Value Measurements (Details 2) - Level 3 $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2019 USD ($) MWh $ / MWh | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | $ (1) | $ 9 | $ 3
NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value | $ | (41) | $ (44) | $ (79)
Model | FTRs |  |  |
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 | $ | $ (41) |  |
Model | Minimum | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value Inputs, RTO Auction Clearing Prices (in $/MWH) | (1.00) |  |
Model | Minimum | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value Inputs, Power (in MWH) | MWh | 400 |  |
Fair Value Inputs, Power, Regional Prices (in $/MWH) | 30.80 |  |
Model | Maximum | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value Inputs, RTO Auction Clearing Prices (in $/MWH) | 1.90 |  |
Model | Maximum | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value Inputs, Power (in MWH) | MWh | 996,000 |  |
Fair Value Inputs, Power, Regional Prices (in $/MWH) | 33.40 |  |
Model | Weighted Average | FTRs |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value Inputs, RTO Auction Clearing Prices (in $/MWH) | 0.40 |  |
Model | Weighted Average | NUG contracts |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |  |  |
Fair Value Inputs, Power (in MWH) | MWh | 205,000 |  |
Fair Value Inputs, Power, Regional Prices (in $/MWH) | 32.10 |  |

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