Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Regulatory assets	$ 6,878	$ 7,124
Asbestos Suits
Site Contingency [Line Items]
Accrued liability	8	8
Regulatory assets	8	8
Workers’ Compensation
Site Contingency [Line Items]
Accrued liability	87	88
Regulatory assets	12	13
CECONY
Site Contingency [Line Items]
Regulatory assets	6,348	6,563
CECONY | Asbestos Suits
Site Contingency [Line Items]
Accrued liability	7	7
Regulatory assets	7	7
CECONY | Workers’ Compensation
Site Contingency [Line Items]
Accrued liability	83	83
Regulatory assets	$ 12	$ 13