Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Site Contingency [Line Items]
Accrued liabilities	$ 734	$ 734
Regulatory assets	4,723	4,987
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	633	640
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	101	94
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	734	734
Regulatory assets	729	732
CECONY
Site Contingency [Line Items]
Accrued liabilities	654	654
Regulatory assets	4,349	4,600
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	554	561
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	100	93
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	654	654
Regulatory assets	$ 648	$ 647