Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Steam) (Details) - CECONY - Steam - USD ($)	12 Months Ended					36 Months Ended
	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
Cost reconciliation, deferred net regulatory liabilities	(1,000,000)	14,000,000	$ 8,000,000		42,000,000	$ 8,000,000
Cost reconciliation, deferred net regulatory assets				17,000,000
Net utility plant reconciliations	0	0			100,000
Authorized return on common equity (percent)						9.30%
Earnings sharing (percent)			9.90%			9.90%
Earnings sharing, threshold limit	$ 14,200,000	8,500,000	$ 7,800,000	$ 11,500,000	$ 0
Earnings sharing, positive adjustment		$ 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%