Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 3,298		$ 9,117
Total revenues	3,328	$ 3,211	9,388	$ 9,072
Other
Disaggregation of Revenue [Line Items]
Total revenues	30		271
Clean Energy Businesses | Renewables | Engineering, procurement and construction
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3		100
CECONY
Disaggregation of Revenue [Line Items]
Total revenues	2,899	2,799	8,121	7,948
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	3,328	3,211	9,388	9,072
Operating Segments | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	92		338
Total revenues	181	177	573	460
Operating Segments | Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Total revenues	89		235
Operating Segments | Clean Energy Businesses | Renewables
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	68		273
Total revenues	68		273
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	24		65
Total revenues	24		65
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	89		235
Operating Segments | Clean Energy Businesses | Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	89		235
Operating Segments | Con Edison Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1		3
Total revenues	1	1	3	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	2,959		8,089
Total revenues	2,899	2,799	8,121	7,948
Operating Segments | CECONY | Other
Disaggregation of Revenue [Line Items]
Total revenues	(60)		32
Operating Segments | CECONY | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,631		6,106
Total revenues	2,571	2,469	6,107	6,079
Operating Segments | CECONY | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	(60)		1
Operating Segments | CECONY | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	264		1,516
Total revenues	264	268	1,540	1,421
Operating Segments | CECONY | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	0		24
Operating Segments | CECONY | Steam
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	64		467
Total revenues	64	62	474	448
Operating Segments | CECONY | Steam | Other
Disaggregation of Revenue [Line Items]
Total revenues	0		7
Operating Segments | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	246		687
Total revenues	246	234	691	667
Operating Segments | O&R | Other
Disaggregation of Revenue [Line Items]
Total revenues	0		4
Operating Segments | O&R | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	215		508
Total revenues	212	206	505	495
Operating Segments | O&R | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	(3)		(3)
Operating Segments | O&R | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31		179
Total revenues	34	28	186	172
Operating Segments | O&R | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	3		7
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0		0
Total revenues	1	$ 0	0	$ (4)
Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 1		$ 0