Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Detail)	9 Months Ended
	Sep. 30, 2016 DTH MWh MW gal
Electric Energy Derivative
Derivatives, Fair Value [Line Items]
Electric Energy (MWH) | MWh	22,797,395
Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
Capacity (MW) | MW	15,472
Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Natural Gas (Dt) | DTH	69,954,738
Refined Fuels
Derivatives, Fair Value [Line Items]
Refined fuel (gallons) | gal	1,344,000
CECONY | Electric Energy Derivative
Derivatives, Fair Value [Line Items]
Electric Energy (MWH) | MWh	20,724,225
CECONY | Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
Capacity (MW) | MW	9,000
CECONY | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Natural Gas (Dt) | DTH	70,100,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Refined fuel (gallons) | gal	1,344,000