Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Steam) (Details) - CECONY - Steam - USD ($)	12 Months Ended						36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Amortization to income of net regulatory (assets) and liabilities							$ 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		42,000,000	$ 8,000,000
Cost reconciliation, deferred net regulatory assets	1,000,000	1,000,000			17,000,000
Increase (decrease) in regulatory liabilities	0	0	0			(100,000)
Authorized return on common equity (percent)							9.30%
Earnings sharing (percent)				9.90%			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 (percent)							48.00%
Other regulatory liabilities				$ 8,000,000			$ 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 (percent)				5.17%			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 (percent)				5.23%			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 (percent)				5.39%			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%