Summary of Significant Accounting Policies - Capitalized Cost of Utility Plant (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 2,336	$ 2,302
Held for future use	73	73
Construction work in progress	1,393	1,027
Net Utility Plant	27,795	26,301
Electric [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Generation	452	434
Electric [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	2,776	2,698
Electric Distribution [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	15,277	14,658
Gas [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Gas	4,469	4,170
Steam [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,790	1,674
General [Member]
Public Utility, Property, Plant and Equipment [Line Items]
General	1,565	1,567
CECONY [Member]
Public Utility, Property, Plant and Equipment [Line Items]
General	2,154	2,126
Held for future use	62	62
Construction work in progress	1,303	947
Net Utility Plant	26,146	24,739
CECONY [Member] | Electric [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Generation	452	434
CECONY [Member] | Electric [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	2,597	2,518
CECONY [Member] | Electric Distribution [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	14,496	13,930
CECONY [Member] | Gas [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Gas	4,013	3,735
CECONY [Member] | Steam [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Steam	1,790	1,674
CECONY [Member] | General [Member]
Public Utility, Property, Plant and Equipment [Line Items]
General	$ 1,433	$ 1,439