Financial Information by Business Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 3,364	$ 3,228
Depreciation and amortization	348	329
Operating income/(loss)	755	812
Clean Energy Businesses
Segment Reporting Information [Line Items]
Total revenues	233
Depreciation and amortization	19	17
Operating income/(loss)	9	15
Con Edison Transmission
Segment Reporting Information [Line Items]
Total revenues	1
Operating income/(loss)	(1)	(3)
CECONY
Segment Reporting Information [Line Items]
Total revenues	2,884	2,856
Depreciation and amortization	310	294
Operating income/(loss)	705	741
CECONY | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	240	229
Operating income/(loss)	254	320
CECONY | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	49	44
Operating income/(loss)	321	298
CECONY | Steam
Segment Reporting Information [Line Items]
Depreciation and amortization	21	21
Operating income/(loss)	130	123
O&R
Segment Reporting Information [Line Items]
Total revenues	246
Depreciation and amortization	19	17
Operating income/(loss)	44	58
O&R | Electric
Segment Reporting Information [Line Items]
Depreciation and amortization	14	12
Operating income/(loss)	8	18
O&R | Gas
Segment Reporting Information [Line Items]
Depreciation and amortization	5	5
Operating income/(loss)	36	40
Operating segment
Segment Reporting Information [Line Items]
Total revenues	3,364	3,228
Operating segment | Clean Energy Businesses
Segment Reporting Information [Line Items]
Total revenues	233	136
Operating segment | Con Edison Transmission
Segment Reporting Information [Line Items]
Total revenues	1	0
Operating segment | CECONY
Segment Reporting Information [Line Items]
Total revenues	2,884	2,856
Operating segment | CECONY | Electric
Segment Reporting Information [Line Items]
Total revenues	1,729	1,793
Operating segment | CECONY | Gas
Segment Reporting Information [Line Items]
Total revenues	841	765
Operating segment | CECONY | Steam
Segment Reporting Information [Line Items]
Total revenues	314	298
Operating segment | O&R
Segment Reporting Information [Line Items]
Total revenues	246	238
Operating segment | O&R | Electric
Segment Reporting Information [Line Items]
Total revenues	149	141
Operating segment | O&R | Gas
Segment Reporting Information [Line Items]
Total revenues	97	97
Other
Segment Reporting Information [Line Items]
Total revenues	0	(2)
Depreciation and amortization	0	1
Operating income/(loss)	(2)	1
Inter-segment | CECONY
Segment Reporting Information [Line Items]
Total revenues	(24)	(24)
Inter-segment | CECONY | Electric
Segment Reporting Information [Line Items]
Total revenues	4	5
Inter-segment | CECONY | Gas
Segment Reporting Information [Line Items]
Total revenues	1	1
Inter-segment | CECONY | Steam
Segment Reporting Information [Line Items]
Total revenues	$ 19	$ 18