Summary of Significant Accounting Policies - Plant and Depreciation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Public Utility, Property, Plant and Equipment [Line Items]
Annual aggregate depreciation allowance	$ 1,253
Non-Utility Plant | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	3 years
Non-Utility Plant | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	30 years
CECONY
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC rates (percent)	5.50%	4.70%	4.40%
Average depreciation rates (percent)	3.10%	3.10%	3.10%
Annual aggregate depreciation allowance	$ 1,184
CECONY | Electric | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
CECONY | Electric | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	95 years
CECONY | Gas | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
CECONY | Gas | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	100 years
CECONY | Steam | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
CECONY | Steam | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	80 years
CECONY | General Plant | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
CECONY | General Plant | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	55 years
O&R
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC rates (percent)	2.50%	3.50%	0.40%
Average depreciation rates (percent)	2.90%	2.90%	3.00%
O&R | Electric | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
O&R | Electric | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	75 years
O&R | Gas | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
O&R | Gas | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	75 years
O&R | General Plant | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	5 years
O&R | General Plant | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	50 years