Summary of Significant Accounting Policies - Capitalized Cost of Utility Plant (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 2,719	$ 2,622
Held for future use	74	77
Construction work in progress	1,175	1,003
NET UTILITY PLANT	33,045	31,133
Electric Generation
Public Utility, Property, Plant and Equipment [Line Items]
Generation	479	459
Electric Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	3,184	3,045
Electric Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	18,150	17,244
Gas
Public Utility, Property, Plant and Equipment [Line Items]
Gas	6,285	5,698
Steam
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,882	1,849
General
Public Utility, Property, Plant and Equipment [Line Items]
General	1,816	1,758
CECONY
Public Utility, Property, Plant and Equipment [Line Items]
General	2,490	2,411
Held for future use	65	65
Construction work in progress	1,104	922
NET UTILITY PLANT	31,115	29,310
CECONY | Electric Generation
Public Utility, Property, Plant and Equipment [Line Items]
Generation	479	459
CECONY | Electric Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	2,963	2,833
CECONY | Electric Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	17,234	16,394
CECONY | Gas
Public Utility, Property, Plant and Equipment [Line Items]
Gas	5,749	5,196
CECONY | Steam
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,882	1,849
CECONY | General
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 1,639	$ 1,592