Fair Value Measurements - Schedule of Commodity Derivatives (Details) - Level 3 $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) $ / kW-month $ / MWh
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (20)
CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	(14)
Electricity
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	(21)
Electricity | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ (15)
Electricity | Forward Energy Prices | Minimum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per MWH) | $ / MWh	19.00
Electricity | Forward Energy Prices | Minimum | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per MWH) | $ / MWh	20.50
Electricity | Forward Energy Prices | Maximum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per MWH) | $ / MWh	76.25
Electricity | Forward Energy Prices | Maximum | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per MWH) | $ / MWh	76.25
Electricity | Forward Capacity Prices | Minimum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per kW-month) | $ / kW-month	1.26
Electricity | Forward Capacity Prices | Maximum
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (dollar per kW-month) | $ / kW-month	9.47
Transmission Congestion Contracts/Financial Transmission Rights
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ 1
Transmission Congestion Contracts/Financial Transmission Rights | Discount for Inter Zonal Forward Price Curves
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (percentage)	50.00%
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 MWH) | $ / MWh	0.50
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 MWH) | $ / MWh	6.75
Transmission Congestion Contracts
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives | $	$ 1
Transmission Congestion Contracts | Discount for Inter Zonal Forward Price Curves | CECONY
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range (percentage)	50.00%