Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Site Contingency [Line Items]
Accrued liabilities	$ 737	$ 734
Regulatory assets	4,875	4,987
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	636	640
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	101	94
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	737	734
Regulatory assets	735	732
CECONY
Site Contingency [Line Items]
Accrued liabilities	657	654
Regulatory assets	4,490	4,600
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	557	561
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	100	93
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	657	654
Regulatory assets	$ 652	$ 647