Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Details)	Jun. 30, 2021 MMBTU MW MWh gal
Electric Energy (MWh)
Derivatives, Fair Value [Line Items]
Notional amount | MWh	24,666,400
Capacity (MW)
Derivatives, Fair Value [Line Items]
Notional amount | MW	43,283
Natural Gas (Dt)
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	272,683,743
Refined Fuels (gallons)
Derivatives, Fair Value [Line Items]
Notional amount | gal	5,712,000
CECONY | Electric Energy (MWh) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | MWh	22,011,350
CECONY | Capacity (MW) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | MW	30,600
CECONY | Natural Gas (Dt) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	252,800,000
CECONY | Refined Fuels (gallons) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | gal	5,172,000