Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Site Contingency [Line Items]
Accrued Liabilities	$ 857	$ 734
Regulatory assets	6,461	4,987
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	752	640
Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	105	94
Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	857	734
Regulatory assets	865	732
CECONY
Site Contingency [Line Items]
Accrued Liabilities	780	654
Regulatory assets	5,989	4,600
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	676	561
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	104	93
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	780	654
Regulatory assets	$ 791	$ 647