Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 251	$ 233
Operating income	526	561
CECONY - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,814	1,735
Inter-segment revenues	4	3
Depreciation and amortization	185	173
Operating income	189	224
CECONY - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	660	563
Inter-segment revenues	1	1
Depreciation and amortization	32	29
Operating income	242	221
CECONY - Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	332	263
Inter-segment revenues	19	19
Depreciation and amortization	16	16
Operating income	129	99
O&R - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	145	128
Depreciation and amortization	10	9
Operating income	20	8
O&R - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	82	82
Depreciation and amortization	4	4
Operating income	27	30
Competitive energy businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	152	310
Inter-segment revenues	2	2
Depreciation and amortization	4	2
Operating income	(82)	(20)
Other Revenues And Eliminations In Segment Information [Member]
Segment Reporting Information [Line Items]
Operating revenues	(1)	(3)
Inter-segment revenues	(2)	(2)
Operating income	1	(1)
Consolidation adjustments [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(24)	(23)
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,806	2,561
Depreciation and amortization	233	218
Operating income	560	544
O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	227	210
Depreciation and amortization	14	13
Operating income	47	38
Con Edison [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,184	3,078
Depreciation and amortization	251	233
Operating income	$ 526	$ 561