Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Details) gal in Thousands	Dec. 31, 2016 MW MMBTU gal MWh
Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	21,235,830
Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	13,616
Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	77,248,786
Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	3,696
CECONY | Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	19,258,400
CECONY | Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	7,500
CECONY | Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	71,060,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	3,696