Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Site Contingency [Line Items]
Accrued liabilities	$ 726	$ 734
Regulatory assets	4,821	4,987
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	625	640
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	101	94
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	726	734
Regulatory assets	723	732
CECONY
Site Contingency [Line Items]
Accrued liabilities	647	654
Regulatory assets	4,422	4,600
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	547	561
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	100	93
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	647	654
Regulatory assets	$ 645	$ 647