Summary of Significant Accounting Policies and Other Matters - Capitalized Cost of Utility Plant (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 3,880	$ 3,562
Held for future use	92	75
Construction work in progress	2,474	1,937
NET UTILITY PLANT	42,024	39,751
Electric Generation
Public Utility, Property, Plant and Equipment [Line Items]
Generation	572	591
Electric Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	3,786	3,634
Electric Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	21,481	20,676
General
Public Utility, Property, Plant and Equipment [Line Items]
General	52	43
Gas
Public Utility, Property, Plant and Equipment [Line Items]
Gas	9,206	8,617
Steam
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,854	1,813
General
Public Utility, Property, Plant and Equipment [Line Items]
General	2,507	2,365
CECONY
Public Utility, Property, Plant and Equipment [Line Items]
General	3,585	3,271
Held for future use	84	67
Construction work in progress	2,320	1,812
NET UTILITY PLANT	39,552	37,412
CECONY | Electric Generation
Public Utility, Property, Plant and Equipment [Line Items]
Generation	572	591
CECONY | Electric Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	3,496	3,380
CECONY | Electric Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	20,366	19,602
CECONY | General
Public Utility, Property, Plant and Equipment [Line Items]
General	52	43
CECONY | Gas
Public Utility, Property, Plant and Equipment [Line Items]
Gas	8,522	7,961
CECONY | Steam
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,854	1,813
CECONY | General
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 2,286	$ 2,143