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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 3,390	$ 3,484	$ 10,091	$ 9,487
Depreciation and amortization	270	258	796	764
Operating income	819	855	1,959	1,767
CECONY [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	250	237	737	705
Operating income	756	752	1,786	1,659
CECONY [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	198	188	581	559
Operating income	811	811	1,416	1,307
CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	33	33	98	97
Operating income	(14)	(24)	273	272
CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	19	16	58	49
Operating income	(41)	(35)	97	80
Orange and Rockland Utilities, Inc. [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	16	14	45	42
Operating income	43	39	102	101
Orange and Rockland Utilities, Inc. [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	12	10	33	31
Operating income	51	46	87	81
Orange and Rockland Utilities, Inc. [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	4	4	12	11
Operating income	(8)	(7)	15	20
Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	3	6	14	16
Operating income	20	63	70	7
Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	1	1		1
Operating income		1	1
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,390	3,484	10,091	9,487
Operating Segments [Member] | CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,838	2,893	8,479	8,021
Operating Segments [Member] | CECONY [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,582	2,622	6,635	6,309
Operating Segments [Member] | CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	210	199	1,359	1,190
Operating Segments [Member] | CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	46	72	485	522
Operating Segments [Member] | Orange and Rockland Utilities, Inc. [Member]
Segment Reporting Information [Line Items]
Operating revenues	232	226	680	635
Operating Segments [Member] | Orange and Rockland Utilities, Inc. [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	205	200	525	492
Operating Segments [Member] | Orange and Rockland Utilities, Inc. [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	27	26	155	143
Operating Segments [Member] | Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	321	365	934	834
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	(1)		(2)	(3)
Inter-Segment Revenues [Member] | CECONY [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	4	4	12	12
Inter-Segment Revenues [Member] | CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1	1	4	4
Inter-Segment Revenues [Member] | CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	21	22	62	60
Inter-Segment Revenues [Member] | CECONY [Member] | Consolidation Adjustments [Member]
Segment Reporting Information [Line Items]
Operating revenues	(26)	(27)	(78)	(76)
Inter-Segment Revenues [Member] | Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	(3)		(2)	4
Inter-Segment Revenues [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 3		$ 2	$ (4)