Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Site Contingency [Line Items]
Accrued Liabilities	$ 779	$ 737
Regulatory assets	4,370	4,333
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	689	651
Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	90	86
Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	779	737
Regulatory assets	810	793
CECONY
Site Contingency [Line Items]
Accrued Liabilities	693	637
Regulatory assets	3,987	3,925
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	603	551
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	90	86
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	693	637
Regulatory assets	$ 716	$ 677