Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Site Contingency [Line Items]
Accrued liabilities	$ 734	$ 737
Regulatory assets	4,407	4,333
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	649	651
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	85	86
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	734	737
Regulatory assets	783	793
CECONY
Site Contingency [Line Items]
Accrued liabilities	634	637
Regulatory assets	3,986	3,925
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	549	551
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	85	86
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	634	637
Regulatory assets	$ 668	$ 677