Summary of Significant Accounting Policies and Other Matters - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 3,328	$ 3,333
Total revenues	3,514	3,364
Other
Disaggregation of Revenue [Line Items]
Total revenues	186	31
Clean Energy Businesses | Renewables | Engineering, procurement and construction
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2	89
CECONY
Disaggregation of Revenue [Line Items]
Total revenues	3,039	2,884
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	3,514	3,364
Operating Segments | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	129	149
Total revenues	217	233
Operating Segments | Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Total revenues	88	84
Operating Segments | Clean Energy Businesses | Renewables
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	106	132
Total revenues	106	132
Operating Segments | Clean Energy Businesses | Renewables | Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Clean Energy Businesses | Energy services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	23	17
Total revenues	23	17
Operating Segments | Clean Energy Businesses | Energy services | Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Total revenues	88	84
Operating Segments | Clean Energy Businesses | Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	88	84
Operating Segments | Con Edison Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1	1
Total revenues	1	1
Operating Segments | Con Edison Transmission | Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,941	2,921
Total revenues	3,039	2,884
Operating Segments | CECONY | Other
Disaggregation of Revenue [Line Items]
Total revenues	98	(37)
Operating Segments | CECONY | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,714	1,771
Total revenues	1,797	1,729
Operating Segments | CECONY | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	83	(42)
Operating Segments | CECONY | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	910	835
Total revenues	921	841
Operating Segments | CECONY | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	11	6
Operating Segments | CECONY | Steam
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	317	315
Total revenues	321	314
Operating Segments | CECONY | Steam | Other
Disaggregation of Revenue [Line Items]
Total revenues	4	(1)
Operating Segments | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	257	262
Total revenues	258	246
Operating Segments | O&R | Other
Disaggregation of Revenue [Line Items]
Total revenues	1	(16)
Operating Segments | O&R | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	143	152
Total revenues	145	149
Operating Segments | O&R | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	2	(3)
Operating Segments | O&R | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	114	110
Total revenues	113	97
Operating Segments | O&R | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	$ (1)	$ (13)