Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Accrued liabilities	$ 745	$ 753
Regulatory assets	6,878	7,124
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	659	664
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	86	89
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	745	753
Regulatory assets	803	823
CECONY
Site Contingency [Line Items]
Accrued liabilities	648	655
Regulatory assets	6,348	6,563
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	563	567
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	85	88
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	648	655
Regulatory assets	$ 690	$ 711