Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Accrued Liabilities	$ 746	$ 753
Regulatory assets	7,169	7,124
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	659	664
Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	87	89
Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	746	753
Regulatory assets	808	823
CECONY
Site Contingency [Line Items]
Accrued Liabilities	649	655
Regulatory assets	6,605	6,563
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	562	567
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	87	88
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	649	655
Regulatory assets	$ 697	$ 711