Financial Information by Business Segment - Financial Data for Business Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 3,156	$ 3,616
Depreciation and amortization	297	279
Operating income	642	726
CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,632	3,010
Depreciation and amortization	272	257
Operating income	640	684
CECONY | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	213	202
Operating income	273	279
CECONY | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	38	35
Operating income	253	241
CECONY | Steam
Segment Reporting Information [Line Items]
Depreciation and amortization	21	20
Operating income	114	164
O&R
Segment Reporting Information [Line Items]
Depreciation and amortization	17	17
Operating income	53	45
O&R | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	12	12
Operating income	18	18
O&R | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	5	5
Operating income	35	27
Competitive energy businesses
Segment Reporting Information [Line Items]
Depreciation and amortization	9	5
Operating income	(51)	(3)
Other
Segment Reporting Information [Line Items]
Depreciation and amortization	(1)	0
Operating income	0	0
Operating revenues
Segment Reporting Information [Line Items]
Operating revenues	3,156	3,616
Operating revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	2,632	3,010
Operating revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	1,773	1,980
Operating revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	601	655
Operating revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	258	375
Operating revenues | O&R
Segment Reporting Information [Line Items]
Operating revenues	215	233
Operating revenues | O&R | Electric
Segment Reporting Information [Line Items]
Operating revenues	140	156
Operating revenues | O&R | Gas
Segment Reporting Information [Line Items]
Operating revenues	75	77
Operating revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	310	374
Operating revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	(1)	(1)
Inter-segment revenues | CECONY
Segment Reporting Information [Line Items]
Operating revenues	(27)	(27)
Inter-segment revenues | CECONY | Electric
Segment Reporting Information [Line Items]
Operating revenues	4	4
Inter-segment revenues | CECONY | Gas
Segment Reporting Information [Line Items]
Operating revenues	1	1
Inter-segment revenues | CECONY | Steam
Segment Reporting Information [Line Items]
Operating revenues	22	22
Inter-segment revenues | Competitive energy businesses
Segment Reporting Information [Line Items]
Operating revenues	6	(3)
Inter-segment revenues | Other
Segment Reporting Information [Line Items]
Operating revenues	$ (6)	$ 3