Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 3,484	$ 3,438	$ 9,487	$ 9,287
Inter-segment revenues
Depreciation and amortization	258	240	764	709
Operating income	855	851	1,767	1,886
Competitive energy businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	365	344	834	954
Inter-segment revenues		2	4	6
Depreciation and amortization	6	2	16	6
Operating income	63	53	7	111
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues			(3)	(6)
Inter-segment revenues		(2)	(4)	(6)
Depreciation and amortization	1		1
Operating income	1			(3)
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,893	2,868	8,021	7,738
Inter-segment revenues
Depreciation and amortization	237	225	705	664
Operating income	752	754	1,659	1,678
CECONY [Member] | Operating Segments [Member] | CECONY - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,622	2,611	6,309	6,307
Inter-segment revenues	4	4	12	11
Depreciation and amortization	188	179	559	527
Operating income	811	812	1,307	1,383
CECONY [Member] | Operating Segments [Member] | CECONY - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	199	189	1,190	1,017
Inter-segment revenues	1	1	4	4
Depreciation and amortization	33	31	97	89
Operating income	(24)	(21)	272	255
CECONY [Member] | Operating Segments [Member] | CECONY - Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	72	68	522	414
Inter-segment revenues	22	20	60	58
Depreciation and amortization	16	15	49	48
Operating income	(35)	(37)	80	40
CECONY [Member] | Consolidation adjustments [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues	(27)	(25)	(76)	(73)
Depreciation and amortization
Operating income
O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	226	226	635	601
Inter-segment revenues
Depreciation and amortization	14	13	42	39
Operating income	39	44	101	100
O&R [Member] | Operating Segments [Member] | CECONY - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	200	199	492	457
Inter-segment revenues
Depreciation and amortization	10	10	31	28
Operating income	46	50	81	74
O&R [Member] | Operating Segments [Member] | CECONY - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	26	27	143	144
Inter-segment revenues
Depreciation and amortization	4	3	11	11
Operating income	$ (7)	$ (6)	$ 20	$ 26