Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 2,911	$ 2,818	$ 6,700	$ 6,003
Depreciation and amortization	265	255	526	506
Operating income	455	386	1,140	912
Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	284	317	612	469
Inter-segment revenues	(1)	2	1	4
Depreciation and amortization	4	5	11	10
Operating income	48	27	50	(56)
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	(1)	(1)	(1)	(1)
Inter-segment revenues	1	(2)	(1)	(4)
Depreciation and amortization	(1)	1
Operating income	1		1	1
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,436	2,321	5,641	5,127
Depreciation and amortization	247	235	486	468
Operating income	386	346	1,030	906
CECONY [Member] | Operating Segments [Member] | CECONY-Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,978	1,872	4,053	3,686
Inter-segment revenues	4	4	8	8
Depreciation and amortization	195	186	383	371
Operating income	347	307	605	495
CECONY [Member] | Operating Segments [Member] | CECONY-Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	360	331	1,149	991
Inter-segment revenues	2	2	3	3
Depreciation and amortization	33	32	64	64
Operating income	54	53	287	296
CECONY [Member] | Operating Segments [Member] | CECONY-Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	98	118	439	450
Inter-segment revenues	21	19	41	38
Depreciation and amortization	19	17	39	33
Operating income	(15)	(14)	138	115
CECONY [Member] | Consolidation Adjustments [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(27)	(25)	(52)	(49)
Orange and Rockland Utilities, Inc. [Member]
Segment Reporting Information [Line Items]
Operating revenues	192	181	448	408
Depreciation and amortization	15	14	29	28
Operating income	20	13	59	61
Orange and Rockland Utilities, Inc. [Member] | Operating Segments [Member] | O&R - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	157	146	320	291
Depreciation and amortization	11	10	21	20
Operating income	25	14	37	34
Orange and Rockland Utilities, Inc. [Member] | Operating Segments [Member] | O&R - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	35	35	128	117
Depreciation and amortization	4	4	8	8
Operating income	$ (5)	$ (1)	$ 22	$ 27