Summary of Significant Accounting Policies and Other Matters - Capitalized Cost of Utility Plant (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 3,331	$ 3,008
Held for future use	76	76
Construction work in progress	1,978	1,605
NET UTILITY PLANT	37,580	35,273
Electric Generation
Public Utility, Property, Plant and Equipment [Line Items]
Generation	593	544
Electric Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	3,333	3,210
Electric Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	19,750	18,959
Gas
Public Utility, Property, Plant and Equipment [Line Items]
Gas	7,714	6,976
Steam
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,830	1,798
General
Public Utility, Property, Plant and Equipment [Line Items]
General	2,306	2,105
CECONY
Public Utility, Property, Plant and Equipment [Line Items]
General	3,056	2,753
Held for future use	67	67
Construction work in progress	1,850	1,502
NET UTILITY PLANT	35,370	33,205
CECONY | Electric Generation
Public Utility, Property, Plant and Equipment [Line Items]
Generation	592	544
CECONY | Electric Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	3,106	2,990
CECONY | Electric Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	18,716	17,996
CECONY | Gas
Public Utility, Property, Plant and Equipment [Line Items]
Gas	7,107	6,403
CECONY | Steam
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,830	1,798
CECONY | General
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 2,102	$ 1,905