Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Details) gal in Thousands	Dec. 31, 2018 MW gal MMBTU MWh
Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	28,303,678
Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	18,519
Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	164,668,697
Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	3,780
CECONY | Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	25,458,600
CECONY | Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	10,350
CECONY | Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	151,280,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	3,780