Summary of Significant Accounting Policies and Other Matters - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 12,144	$ 11,928
Total revenues	12,574	12,337	$ 12,033
CECONY
Disaggregation of Revenue [Line Items]
Total revenues	10,821	10,680	10,468
Operating segment | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	646	424
Total revenues	857	763	694
Operating segment | Con Edison Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4	4
Total revenues	4	4	2
Operating segment | CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,620	10,597
Total revenues	10,821	10,680	10,468
Operating segment | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	874	903
Total revenues	893	891	874
Operating segment | Electric | CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,913	7,920
Total revenues	8,062	7,971	7,972
Operating segment | Electric | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	627	647
Total revenues	634	642	642
Operating segment | Gas | CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,097	2,052
Total revenues	2,132	2,078	1,901
Operating segment | Gas | O&R
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	247	256
Total revenues	259	249	232
Operating segment | Steam | CECONY
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	610	625
Total revenues	627	631	595
Operating segment | Renewables | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	575	329
Total revenues	575	329
Operating segment | Energy services | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	71	95
Total revenues	71	95
Operating segment | Other | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Total revenues	211	339
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Total revenues	(1)	(1)	(5)
Other | O&R
Disaggregation of Revenue [Line Items]
Total revenues	0	0	$ 0
Other
Disaggregation of Revenue [Line Items]
Total revenues	430	409
Other | Operating segment | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Total revenues	211	339
Other | Operating segment | Con Edison Transmission
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Other | Operating segment | CECONY
Disaggregation of Revenue [Line Items]
Total revenues	201	83
Other | Operating segment | O&R
Disaggregation of Revenue [Line Items]
Total revenues	19	(12)
Other | Operating segment | Electric | CECONY
Disaggregation of Revenue [Line Items]
Total revenues	149	51
Other | Operating segment | Electric | O&R
Disaggregation of Revenue [Line Items]
Total revenues	7	(5)
Other | Operating segment | Gas | CECONY
Disaggregation of Revenue [Line Items]
Total revenues	35	26
Other | Operating segment | Gas | O&R
Disaggregation of Revenue [Line Items]
Total revenues	12	(7)
Other | Operating segment | Steam | CECONY
Disaggregation of Revenue [Line Items]
Total revenues	17	6
Other | Operating segment | Renewables | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Other | Operating segment | Energy services | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Other | Operating segment | Other | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Total revenues	211	339
Other | Other
Disaggregation of Revenue [Line Items]
Total revenues	(1)	(1)
Engineering, procurement and construction | Renewables | Clean Energy Businesses
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 14	$ 103