Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Details) gal in Thousands	Mar. 31, 2017 gal MMBTU MW MWh
Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	19,410,040
Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	11,631
Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	69,548,736
Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	2,688
CECONY | Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	17,605,375
CECONY | Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	6,000
CECONY | Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	62,210,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	2,688