Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Site Contingency [Line Items]
Accrued Liabilities	$ 753	$ 765
Regulatory assets	7,124	8,228
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	664	679
Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	89	86
Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	753	765
Regulatory assets	823	904
CECONY
Site Contingency [Line Items]
Accrued Liabilities	655	665
Regulatory assets	6,563	7,603
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued Liabilities	567	579
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	88	86
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued Liabilities	655	665
Regulatory assets	$ 711	$ 800