Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 3,789	$ 3,184
Inter-segment revenues
Depreciation and amortization	261	251
Operating income	685	526
Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	329	152
Inter-segment revenues	3	2
Depreciation and amortization	7	4
Operating income	2	(82)
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues		(1)
Inter-segment revenues	(3)	(2)
Depreciation and amortization
Operating income	1	1
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,204	2,806
Inter-segment revenues
Depreciation and amortization	240	233
Operating income	643	560
CECONY [Member] | Operating Segments [Member] | CECONY-Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,074	1,814
Inter-segment revenues	4	4
Depreciation and amortization	189	185
Operating income	257	189
CECONY [Member] | Operating Segments [Member] | CECONY-Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	789	660
Inter-segment revenues	1	1
Depreciation and amortization	32	32
Operating income	233	242
CECONY [Member] | Operating Segments [Member] | CECONY-Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	341	332
Inter-segment revenues	20	19
Depreciation and amortization	19	16
Operating income	153	129
CECONY [Member] | Consolidation Adjustments [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues	(25)	(24)
Depreciation and amortization
Operating income
O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	256	227
Inter-segment revenues
Depreciation and amortization	14	14
Operating income	39	47
O&R [Member] | Operating Segments [Member] | O&R - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	163	145
Inter-segment revenues
Depreciation and amortization	10	10
Operating income	12	20
O&R [Member] | Operating Segments [Member] | O&R - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	93	82
Inter-segment revenues
Depreciation and amortization	4	4
Operating income	$ 27	$ 27