Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Details) gal in Thousands	Jun. 30, 2017 gal MMBTU MW MWh
Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	33,854,855
Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	9,319
Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	99,241,963
Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	1,680
CECONY | Electric Energy
Derivatives, Fair Value [Line Items]
Notional amount | MWh	31,442,175
CECONY | Capacity
Derivatives, Fair Value [Line Items]
Notional amount | MW	4,500
CECONY | Natural Gas
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	91,970,000
CECONY | Refined Fuels
Derivatives, Fair Value [Line Items]
Notional amount | gal	1,680