Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Detail)	9 Months Ended
	Sep. 30, 2015 DTH MWh MW gal
Electric Energy Derivative
Derivatives, Fair Value [Line Items]
Electric Energy (MWHs) | MWh	18,475,688
Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
Capacity (MWs)	7,201
Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Natural Gas (Dt) | DTH	63,386,967
Refined Fuels
Derivatives, Fair Value [Line Items]
Refined fuel (gallons) | gal	4,620,000
CECONY | Electric Energy Derivative
Derivatives, Fair Value [Line Items]
Electric Energy (MWHs) | MWh	5,972,325
CECONY | Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
Capacity (MWs)	2,400
CECONY | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Natural Gas (Dt) | DTH	56,690,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Refined fuel (gallons) | gal	4,620,000
Discontinued Operations, Held-for-sale | Electric Energy Derivative
Derivatives, Fair Value [Line Items]
Electric Energy (MWHs) | MWh	11,445,799
Discontinued Operations, Held-for-sale | Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
Capacity (MWs)	5,436
Discontinued Operations, Held-for-sale | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Natural Gas (Dt) | DTH	509,294