Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Site Contingency [Line Items]
Accrued liabilities	$ 850	$ 857
Regulatory assets	6,243	6,461
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	745	752
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	105	105
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	850	857
Regulatory assets	858	865
CECONY
Site Contingency [Line Items]
Accrued liabilities	773	780
Regulatory assets	5,793	5,989
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	669	676
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	104	104
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	773	780
Regulatory assets	$ 786	$ 791