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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 2,818	$ 2,771	$ 6,003	$ 5,849
Inter-segment revenues
Depreciation and amortization	255	236	506	469
Operating income	386	475	912	1,036
Competitive energy businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	317	300	469	610
Inter-segment revenues	2	2	4	4
Depreciation and amortization	5	2	10	4
Operating income	27	78	(56)	59
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	(1)	(2)	(1)	(5)
Inter-segment revenues	(2)	(2)	(4)	(4)
Depreciation and amortization	1
Operating income			1	(3)
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,321	2,309	5,127	4,870
Inter-segment revenues
Depreciation and amortization	235	221	468	439
Operating income	346	380	906	925
CECONY [Member] | Operating Segments [Member] | CECONY - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,872	1,961	3,686	3,696
Inter-segment revenues	4	4	8	7
Depreciation and amortization	186	175	371	348
Operating income	307	348	495	573
CECONY [Member] | Operating Segments [Member] | CECONY - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	331	265	991	828
Inter-segment revenues	2	2	3	3
Depreciation and amortization	32	30	64	59
Operating income	53	54	296	275
CECONY [Member] | Operating Segments [Member] | CECONY - Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	118	83	450	346
Inter-segment revenues	19	19	38	38
Depreciation and amortization	17	16	33	32
Operating income	(14)	(22)	115	77
CECONY [Member] | Consolidation adjustments [Member]
Segment Reporting Information [Line Items]
Operating revenues
Inter-segment revenues	(25)	(25)	(49)	(48)
Depreciation and amortization
Operating income
O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	181	164	408	374
Inter-segment revenues
Depreciation and amortization	14	13	28	26
Operating income	13	17	61	55
O&R [Member] | Operating Segments [Member] | CECONY - Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	146	129	291	257
Inter-segment revenues
Depreciation and amortization	10	9	20	19
Operating income	14	16	34	24
O&R [Member] | Operating Segments [Member] | CECONY - Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	35	35	117	117
Inter-segment revenues
Depreciation and amortization	4	4	8	7
Operating income	$ (1)	$ 1	$ 27	$ 31