Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 2,582		$ 5,819
Total revenues	2,696	$ 2,633	6,060	$ 5,861
Other
Disaggregation of Revenue [Line Items]
Total revenues	114		241
Clean Energy Businesses | Renewables | Engineering, procurement and construction
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9		97
CECONY
Disaggregation of Revenue [Line Items]
Total revenues	2,338	2,293	5,222	5,149
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	2,696	2,633	6,060	5,861
Operating Segments | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	96		246
Total revenues	158	146	391	283
Operating Segments | Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Total revenues	62		145
Operating Segments | Clean Energy Businesses | Renewables
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	73		205
Total revenues	73		205
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		41
Total revenues	23		41
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	62		145
Operating Segments | Clean Energy Businesses | Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	62		145
Operating Segments | Con Edison Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1		2
Total revenues	1	0	2	0
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	2,292		5,130
Total revenues	2,338	2,293	5,222	5,149
Operating Segments | CECONY | Other
Disaggregation of Revenue [Line Items]
Total revenues	46		92
Operating Segments | CECONY | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,771		3,474
Total revenues	1,807	1,817	3,536	3,610
Operating Segments | CECONY | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	36		62
Operating Segments | CECONY | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	428		1,252
Total revenues	435	388	1,276	1,153
Operating Segments | CECONY | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	7		24
Operating Segments | CECONY | Steam
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	93		404
Total revenues	96	88	410	386
Operating Segments | CECONY | Steam | Other
Disaggregation of Revenue [Line Items]
Total revenues	3		6
Operating Segments | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	193		441
Total revenues	198	195	445	433
Operating Segments | O&R | Other
Disaggregation of Revenue [Line Items]
Total revenues	5		4
Operating Segments | O&R | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	146		293
Total revenues	144	148	293	289
Operating Segments | O&R | Electric | Other
Disaggregation of Revenue [Line Items]
Total revenues	(2)		0
Operating Segments | O&R | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	47		148
Total revenues	54	47	152	144
Operating Segments | O&R | Gas | Other
Disaggregation of Revenue [Line Items]
Total revenues	7		4
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0		0
Total revenues	1	$ (1)	0	$ (4)
Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 1		$ 0