Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Detail) - 6 months ended Jun. 30, 2015	DTH MWh MW gal
Electric Energy Derivative
Derivatives, Fair Value [Line Items]
MWHs	20,982,862
Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
MWs | MW	7,324
Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Dths | DTH	61,343,892
Refined Fuels
Derivatives, Fair Value [Line Items]
Gallons | gal	5,502,000
CECONY | Electric Energy Derivative
Derivatives, Fair Value [Line Items]
MWHs	6,941,125
CECONY | Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
MWs | MW	2,400
CECONY | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Dths | DTH	55,640,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Gallons | gal	5,502,000
Discontinued Operations, Held-for-sale | Electric Energy Derivative
Derivatives, Fair Value [Line Items]
MWHs	12,801,647
Discontinued Operations, Held-for-sale | Electric Capacity Derivative
Derivatives, Fair Value [Line Items]
MWs | MW	6,635
Discontinued Operations, Held-for-sale | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Dths | DTH	1,397,036