Summary of Significant Accounting Policies and Other Matters - Plant and Depreciation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated amortization	$ 228	$ 126
Annual aggregate depreciation allowance	1,694
Other deferred charges and noncurrent assets	54
Prepaid Expense	12
Depreciation expense, other deferred charges and noncurrent assets and prepayments	7
Accumulated depreciation, other deferred charges and noncurrent assets and prepayments	10
Software Licenses
Public Utility, Property, Plant and Equipment [Line Items]
Gross asset	86	93
Estimated aggregate annual amortization expense	7
Accumulated amortization	$ 17	$ 10
Non-Utility Plant | Maximum | Land And Conduit
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	10 years
Non-Utility Plant | Maximum | Wind Power Generating Assets
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	30 years
Non-Utility Plant | Maximum | Solar Powered Generating Assets
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	35 years
CECONY
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC rates (percent)	5.20%	5.10%	5.40%
Average depreciation rates (percent)	3.50%	3.20%	3.20%
Annual aggregate depreciation allowance	$ 1,604
Other deferred charges and noncurrent assets	51
Prepaid Expense	11
Depreciation expense, other deferred charges and noncurrent assets and prepayments	6
Accumulated depreciation, other deferred charges and noncurrent assets and prepayments	8
CECONY | Software Licenses
Public Utility, Property, Plant and Equipment [Line Items]
Gross asset	81	$ 88
Estimated aggregate annual amortization expense	7
Accumulated amortization	$ 17	$ 10
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)	85 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)	90 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)	5.30%	5.30%	2.20%
Average depreciation rates (percent)	3.20%	3.00%	2.90%
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 | 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