Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Site Contingency [Line Items]
Accrued Liabilities	$ 734	$ 779
Regulatory assets	4,987	4,370
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	640	689
Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	94	90
Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	734	779
Regulatory assets	732	810
CECONY
Site Contingency [Line Items]
Accrued Liabilities	654	693
Regulatory assets	4,600	3,987
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	561	603
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	93	90
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	654	693
Regulatory assets	$ 647	$ 716