Fair Value Measurements - Schedule of Commodity Derivatives (Details) - Level 3 $ in Millions	Dec. 31, 2020 USD ($) $ / kW-month $ / MWh
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	$ (19)
CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	(10)
Electricity | Forward Capacity Prices
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	(20)
Electricity | Forward Capacity Prices | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	$ (11)
Electricity | Forward Capacity Prices | Minimum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	0.06
Electricity | Forward Capacity Prices | Minimum | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	0.08
Electricity | Forward Capacity Prices | Maximum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	6.26
Electricity | Forward Capacity Prices | Maximum | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / kW-month	6.26
Transmission Congestion Contracts | Inter-Zonal Forward Price Curves
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	$ 1
Transmission Congestion Contracts | Inter-Zonal Forward Price Curves | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	$ 1
Transmission Congestion Contracts | Inter-Zonal Forward Price Curves | Minimum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / MWh	(2.65)
Transmission Congestion Contracts | Inter-Zonal Forward Price Curves | Minimum | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / MWh	0.23
Transmission Congestion Contracts | Inter-Zonal Forward Price Curves | Maximum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / MWh	7.69
Transmission Congestion Contracts | Inter-Zonal Forward Price Curves | Maximum | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per unit) | $ / MWh	1.13