Fair Value Measurements - Schedule of Commodity Derivatives (Details) $ in Millions	Sep. 30, 2025 USD ($) $ / kW-month $ / MWh	Dec. 31, 2024 USD ($)
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ 818	$ 741
CECONY | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	790	712
Level 3
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	5	1
Level 3 | CECONY | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	1	$ 1
Level 3 | Electricity | Forward energy prices
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ 0
Level 3 | Electricity | Forward energy prices | Maximum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit)	107.30
Level 3 | Electricity | Forward energy prices | Average Market Price
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	57.58
Level 3 | Electricity | Forward energy prices | Minimum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit)	33.35
Level 3 | Electricity | Forward energy prices | CECONY | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (1)
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)	107.30
Level 3 | Electricity | Forward energy prices | CECONY | Average Market Price | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	57.96
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)	34.45
Level 3 | Electricity | Forward capacity prices
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (13)
Level 3 | Electricity | Forward capacity prices | Maximum | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit)	8.37
Level 3 | Electricity | Forward capacity prices | Average Market Price
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	3.65
Level 3 | Electricity | Forward capacity prices | Minimum | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit)	0.73
Level 3 | Electricity | Forward capacity prices | CECONY | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (7)
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)	7.14
Level 3 | Electricity | Forward capacity prices | CECONY | Average Market Price | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	3.27
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)	0.73
Level 3 | Transmission Congestion Contracts | 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 | 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)	2.85
Level 3 | Transmission Congestion Contracts | Inter-zonal forward price curves adjusted for historical zonal losses | Average Market Price
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit)	1.06
Level 3 | Transmission Congestion Contracts | 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)	(0.03)
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 | $	$ 1
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)	2.85
Level 3 | Transmission Congestion Contracts | Inter-zonal forward price curves adjusted for historical zonal losses | CECONY | Average Market Price | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit)	1.06
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)	(0.03)
Level 3 | Commodity
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (12)
Level 3 | Commodity | CECONY | Subsidiaries
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (7)