Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Accrued Liabilities	$ 745	$ 753
Regulatory assets	7,012	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	807	823
CECONY
Site Contingency [Line Items]
Accrued Liabilities	651	655
Regulatory assets	6,472	6,563
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	565	567
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	86	88
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	651	655
Regulatory assets	$ 697	$ 711