Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 3,333
Other revenues	31
Total operating revenues	3,364	$ 3,228
Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	149
Other revenues	84
Total operating revenues	233
Clean Energy Businesses | Renewables
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	132
Other revenues	0
Total operating revenues	132
Clean Energy Businesses | Renewables | Engineering, procurement and construction
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	89
Clean Energy Businesses | Energy services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	17
Other revenues	0
Total operating revenues	17
Clean Energy Businesses | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Other revenues	84
Total operating revenues	84
Con Edison Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1
Other revenues	0
Total operating revenues	1
CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,921
Other revenues	(37)
Total operating revenues	2,884	$ 2,856
CECONY | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,771
Other revenues	(42)
Total operating revenues	1,729
CECONY | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	835
Other revenues	6
Total operating revenues	841
CECONY | Steam
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	315
Other revenues	(1)
Total operating revenues	314
O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	262
Other revenues	(16)
Total operating revenues	246
O&R | Electric
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	152
Other revenues	(3)
Total operating revenues	149
O&R | Gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	110
Other revenues	(13)
Total operating revenues	$ 97