Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Details)	Sep. 30, 2021 MW gal MWh MMBTU
Electric Energy (MWh)
Derivatives, Fair Value [Line Items]
Notional amount | MWh	23,870,400
Capacity (MW)
Derivatives, Fair Value [Line Items]
Notional amount | MW	39,914
Natural Gas (Dt)
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	280,838,997
Refined Fuels (gallons)
Derivatives, Fair Value [Line Items]
Notional amount | gal	4,704,000
CECONY | Electric Energy (MWh) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | MWh	21,401,150
CECONY | Capacity (MW) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | MW	29,700
CECONY | Natural Gas (Dt) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | MMBTU	261,010,000
CECONY | Refined Fuels (gallons) | Subsidiaries
Derivatives, Fair Value [Line Items]
Notional amount | gal	4,704,000