Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Steam) (Details) - CECONY - Steam - USD ($)	12 Months Ended						36 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Utilities operating expense, depreciation and amortization							$ 37,000,000
Regulatory liabilities, amortization period							3 years
Negative revenue adjustments	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Cost reconciliation, deferred net regulatory liabilities				$ 14,000,000	8,000,000		$ 8,000,000	$ 42,000,000
Cost reconciliation, deferred net regulatory assets	35,000,000	8,000,000	1,000,000			17,000,000
Increase (decrease) in regulatory liabilities	0	0	0			(100,000)
Authorized return on common equity (percent)							930.00%
Earnings sharing (percent)				9.90%
Earnings sharing, threshold limit	$ 5,000,000	16,500,000	8,500,000	$ 7,800,000	$ 11,500,000	$ 0
Earnings sharing, positive adjustment		$ 2,300,000	$ 1,100,000	4,000,000
Common Equity Ratio, Percentage							4800.00%
Other regulatory liabilities				$ 8,000,000
Difference in property taxes (percent)							90.00%
Deferral, annual maximum (not more than) (percent)							10.00%
Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes							$ (22,400,000)
Average rate base							$ 1,511,000,000
Weighted average cost of capital (after-tax) (percent)							7.10%
Actual return on common equity (percent)							9.82%
Cost of long-term debt rate				5.17%
Year 1 | Production
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 1,752,000,000
Year 1 | Distribution
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							6,000,000
Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)							1,000,000
Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes							19,800,000
Average rate base							$ 1,547,000,000
Weighted average cost of capital (after-tax) (percent)							7.13%
Actual return on common equity (percent)							10.88%
Cost of long-term debt rate				5.23%
Year 2 | Production
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 1,732,000,000
Year 2 | Distribution
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							11,000,000
Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)							1,000,000
Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes							20,300,000
Average rate base							$ 1,604,000,000
Weighted average cost of capital (after-tax) (percent)							7.21%
Actual return on common equity (percent)							10.54%
Cost of long-term debt rate				5.39%
Year 3 | Production
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 1,720,000,000
Year 3 | Distribution
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							25,000,000
Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)							1,000,000
Year 4
Public Utilities, General Disclosures [Line Items]
Base rate changes							$ 0
Actual return on common equity (percent)							9.51%
Year 5
Public Utilities, General Disclosures [Line Items]
Base rate changes							$ 0
Actual return on common equity (percent)							11.73%
Year 6
Public Utilities, General Disclosures [Line Items]
Base rate changes							$ 0
Actual return on common equity (percent)							10.45%
Year 7
Public Utilities, General Disclosures [Line Items]
Actual return on common equity (percent)							7.91%