Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 3,616	$ 3,789
Depreciation and amortization	279	261
Operating income	726	685
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,010	3,204
Depreciation and amortization	257	240
Operating income	684	643
CECONY [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	202	189
Operating income	279	257
CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	35	32
Operating income	241	233
CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	20	19
Operating income	164	153
O&R [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	17	14
Operating income	45	39
O&R [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	12	10
Operating income	18	12
O&R [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	5	4
Operating income	27	27
Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	5	7
Operating income	(3)	2
Other [Member]
Segment Reporting Information [Line Items]
Operating income		1
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,616	3,789
Operating Segments [Member] | CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,010	3,204
Operating Segments [Member] | CECONY [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,980	2,074
Operating Segments [Member] | CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	655	789
Operating Segments [Member] | CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	375	341
Operating Segments [Member] | O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	233	256
Operating Segments [Member] | O&R [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	156	163
Operating Segments [Member] | O&R [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	77	93
Operating Segments [Member] | Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	374	329
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	(1)
Inter-Segment Revenues [Member] | CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	(27)	(25)
Inter-Segment Revenues [Member] | CECONY [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	4	4
Inter-Segment Revenues [Member] | CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1	1
Inter-Segment Revenues [Member] | CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	22	20
Inter-Segment Revenues [Member] | Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	(3)	3
Inter-Segment Revenues [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 3	$ (3)