Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Regulatory assets	$ 4,333	$ 7,124
Asbestos Suits
Site Contingency [Line Items]
Accrued liability	8	8
Regulatory assets	8	8
Workers' Compensation
Site Contingency [Line Items]
Accrued liability	84	88
Regulatory assets	10	13
CECONY
Site Contingency [Line Items]
Regulatory assets	3,925	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	80	83
Regulatory assets	$ 10	$ 13