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Fair Value Measurements - Schedule of Commodity Derivatives (Details) $ in Millions | Sep. 30, 2021 USD ($) $ / MWh $ / kW-month | Dec. 31, 2020 USD ($)
--- | --- | ---
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ 1,017 | $ 675
CECONY | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | 898 | 550
Level 3 |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | 29 | 4
Level 3 | CECONY | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | 2 | $ 0
Level 3 | Electricity | Forward energy prices |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ 11 |
Level 3 | Electricity | Forward energy prices | Minimum |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 15.00 |
Level 3 | Electricity | Forward energy prices | Maximum |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 130.75 |
Level 3 | Electricity | Forward energy prices | CECONY | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ (9) |
Level 3 | Electricity | Forward energy prices | CECONY | Minimum | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 26.80 |
Level 3 | Electricity | Forward energy prices | CECONY | Maximum | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 98.51 |
Level 3 | Electricity | Forward capacity prices |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ (17) |
Level 3 | Electricity | Forward capacity prices | Minimum |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / kW-month | 0.26 |
Level 3 | Electricity | Forward capacity prices | Maximum |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / kW-month | 12.93 |
Level 3 | Electricity | Forward capacity prices | CECONY | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ (10) |
Level 3 | Electricity | Forward capacity prices | CECONY | Minimum | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / kW-month | 0.70 |
Level 3 | Electricity | Forward capacity prices | CECONY | Maximum | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / kW-month | 12.93 |
Level 3 | Transmission Congestion Contracts/Financial Transmission Rights | Inter-zonal forward price curves adjusted for historical zonal losses |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ 1 |
Level 3 | Transmission Congestion Contracts/Financial Transmission Rights | Inter-zonal forward price curves adjusted for historical zonal losses | Minimum |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | (4.21) |
Level 3 | Transmission Congestion Contracts/Financial Transmission Rights | Inter-zonal forward price curves adjusted for historical zonal losses | Maximum |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 10.11 |
Level 3 | Commodity |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ (5) |
Level 3 | Commodity | CECONY | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | (17) |
Level 3 | Transmission Congestion Contracts | Inter-zonal forward price curves adjusted for historical zonal losses | CECONY | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Fair Value of commodity derivatives | $ 2 |
Level 3 | Transmission Congestion Contracts | Inter-zonal forward price curves adjusted for historical zonal losses | CECONY | Minimum | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 0.63 |
Level 3 | Transmission Congestion Contracts | Inter-zonal forward price curves adjusted for historical zonal losses | CECONY | Maximum | Subsidiaries |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unobservable Inputs Range (dollar per unit) | $ / MWh | 5.63 |

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