Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Site Contingency [Line Items]
Regulatory assets	$ 4,407	$ 4,333
Asbestos Suits
Site Contingency [Line Items]
Accrued liability	8	8
Regulatory assets	8	8
Workers’ Compensation
Site Contingency [Line Items]
Accrued liability	84	84
Regulatory assets	10	10
CECONY
Site Contingency [Line Items]
Regulatory assets	3,986	3,925
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	80
Regulatory assets	$ 10	$ 10