Summary of Significant Accounting Policies and Other Matters - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 3,337	$ 3,298	$ 9,264	$ 9,117
Total revenues	3,365	3,328	9,623	9,388
Other
Disaggregation of Revenue [Line Items]
Total revenues	28	30	359	271
Clean Energy Businesses | Renewables | Engineering, procurement and construction
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3	3	9	100
CECONY
Disaggregation of Revenue [Line Items]
Total revenues	2,877	2,899	8,248	8,121
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	3,365	3,328	9,623	9,388
Operating Segments | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	207	92	518	338
Total revenues	247	181	696	573
Operating Segments | Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Total revenues	40	89	178	235
Operating Segments | Clean Energy Businesses | Renewables
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	193	68	465	273
Total revenues	193	68	465	273
Operating Segments | Clean Energy Businesses | Renewables | Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Clean Energy Businesses | Energy services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14	24	53	65
Total revenues	14	24	53	65
Operating Segments | Clean Energy Businesses | Energy services | Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Total revenues	40	89	178	235
Operating Segments | Clean Energy Businesses | Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	40	89	178	235
Operating Segments | Con Edison Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1	1	3	3
Total revenues	1	1	3	3
Operating Segments | Con Edison Transmission | Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,899	2,959	8,077	8,089
Total revenues	2,877	2,899	8,248	8,121
Operating Segments | CECONY | Other
Disaggregation of Revenue [Line Items]
Total revenues	(22)	(60)	171	32
Operating Segments | CECONY | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,582	2,631	6,048	6,106
Total revenues	2,544	2,571	6,174	6,107
Operating Segments | CECONY | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	(38)	(60)	126	1
Operating Segments | CECONY | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	263	264	1,573	1,516
Total revenues	275	264	1,605	1,540
Operating Segments | CECONY | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	12	0	32	24
Operating Segments | CECONY | Steam
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	54	64	456	467
Total revenues	58	64	469	474
Operating Segments | CECONY | Steam | Other
Disaggregation of Revenue [Line Items]
Total revenues	4	0	13	7
Operating Segments | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	230	246	666	687
Total revenues	241	246	678	691
Operating Segments | O&R | Other
Disaggregation of Revenue [Line Items]
Total revenues	11	0	12	4
Operating Segments | O&R | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	205	215	488	508
Total revenues	210	212	493	505
Operating Segments | O&R | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	5	(3)	5	(3)
Operating Segments | O&R | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	25	31	178	179
Total revenues	31	34	185	186
Operating Segments | O&R | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	6	3	7	7
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Total revenues	(1)	1	(2)	0
Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	$ (1)	$ 1	$ (2)	$ 0