Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Site Contingency [Line Items]
Accrued liabilities	$ 728	$ 737
Regulatory assets	4,187	4,333
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	645	651
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	83	86
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	728	737
Regulatory assets	772	793
CECONY
Site Contingency [Line Items]
Accrued liabilities	631	637
Regulatory assets	3,779	3,925
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	548	551
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	83	86
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	631	637
Regulatory assets	$ 662	$ 677