Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Gas) (Details) - USD ($)	1 Months Ended	12 Months Ended					36 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2019	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Revenues		$ 12,337,000,000	$ 12,033,000,000	$ 12,075,000,000
Deferred revenues		20,000,000	87,000,000
CECONY
Public Utilities, General Disclosures [Line Items]
Revenues		10,680,000,000	10,468,000,000	10,165,000,000
CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Amortization to income of net regulatory (assets) and liabilities								$ 4,000,000
Regulatory liabilities, amortization period								3 years
Amount of revenues retained	$ 65,000,000			65,000,000	$ 66,000,000	$ 70,000,000		$ 65,000,000
Percentage of revenue reserve								15.00%
Other earnings incentives		6,000,000	7,000,000
Deferred revenues	71,000,000	12,000,000	3,000,000	71,000,000	54,000,000	28,000,000		$ 71,000,000
Negative revenue adjustments		0	5,000,000	0	0	0
Cost reconciliation, deferred net regulatory liabilities	$ 32,000,000		2,000,000	$ 32,000,000	11,000,000	38,000,000		$ 32,000,000
Cost reconciliation, deferred net regulatory assets		44,000,000
Net utility plant reconciliations		2,200,000	2,200,000		1,000,000
Earnings sharing (percent)	9.90%			9.90%				9.90%
Earnings sharing, threshold limit		0	$ 0	$ 0	0	0
Common equity ratio (percent)								48.00%
Base rate change deferral regulatory liability impact	$ 32,000,000			32,000,000				$ 32,000,000
Increase in gas base rate due to expiration of temporary credit under the prior rate plan	41,000,000
Difference in property taxes (percent)								90.00%
CECONY | Gas | Maximum
Public Utilities, General Disclosures [Line Items]
Amount of revenues retained	$ 65,000,000			65,000,000				$ 65,000,000
Potential penalties (annually)				$ 56,000,000	$ 44,000,000	$ 33,000,000
CECONY | Gas | Gas Leak Backlog, Leak Prone Pipe and Service Terminations
Public Utilities, General Disclosures [Line Items]
Revenues		$ 5,000,000
CECONY | Gas | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Percentage of revenue reserve							15.00%
Earnings sharing (percent)							9.50%
Common equity ratio (percent)							48.00%
Deferral, annual maximum (not more than) (percent)							10.00%
CECONY | Gas | Scenario, Forecast | Maximum
Public Utilities, General Disclosures [Line Items]
Amount of revenues retained							$ 65,000,000
CECONY | Gas | Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes								(54,600,000)
Average rate base								$ 3,521,000,000
Weighted average cost of capital (after-tax) (percent)								7.10%
Authorized return on common equity (percent)								9.30%
Actual return on common equity (percent)								8.02%
Cost of long-term debt (percent)	5.17%			5.17%				5.17%
CECONY | Gas | Year 1 | Gas delivery
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 3,899,000,000
CECONY | Gas | Year 1 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								3,000,000
CECONY | Gas | Year 1 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes							(5,000,000)
Amortization to income of net regulatory (assets) and liabilities							39,000,000
Potential incentives if performance targets are met							7,000,000
Potential penalties (annually)							68,000,000
Average rate base							$ 4,841,000,000
Weighted average cost of capital (after-tax) (percent)							6.82%
Authorized return on common equity (percent)							9.00%
Actual return on common equity (percent)							9.22%
Cost of long-term debt (percent)							4.93%
CECONY | Gas | Year 1 | Scenario, Forecast | Gas average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 5,844,000,000
CECONY | Gas | Year 1 | Scenario, Forecast | AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							27,000,000
CECONY | Gas | Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes								38,600,000
Average rate base								$ 3,863,000,000
Weighted average cost of capital (after-tax) (percent)								7.13%
Actual return on common equity (percent)								8.13%
Cost of long-term debt (percent)	5.23%			5.23%				5.23%
CECONY | Gas | Year 2 | Gas delivery
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 4,258,000,000
CECONY | Gas | Year 2 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								8,000,000
CECONY | Gas | Year 2 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes							92,000,000
Amortization to income of net regulatory (assets) and liabilities							37,000,000
Potential incentives if performance targets are met							8,000,000
Potential penalties (annually)							63,000,000
Average rate base							$ 5,395,000,000
Weighted average cost of capital (after-tax) (percent)							6.80%
Actual return on common equity (percent)							9.04%
Cost of long-term debt (percent)							4.88%
CECONY | Gas | Year 2 | Scenario, Forecast | Gas average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 6,512,000,000
CECONY | Gas | Year 2 | Scenario, Forecast | AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							57,000,000
CECONY | Gas | Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes								56,800,000
Average rate base								$ 4,236,000,000
Weighted average cost of capital (after-tax) (percent)								7.21%
Actual return on common equity (percent)								7.83%
Cost of long-term debt (percent)	5.39%			5.39%				5.39%
CECONY | Gas | Year 3 | Gas delivery
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 4,698,000,000
CECONY | Gas | Year 3 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 30,000,000
CECONY | Gas | Year 3 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes							90,000,000
Amortization to income of net regulatory (assets) and liabilities							36,000,000
Potential incentives if performance targets are met							8,000,000
Potential penalties (annually)							70,000,000
Average rate base							$ 6,005,000,000
Weighted average cost of capital (after-tax) (percent)							6.73%
Cost of long-term debt (percent)							4.74%
CECONY | Gas | Year 3 | Scenario, Forecast | Gas average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 7,177,000,000
CECONY | Gas | Year 3 | Scenario, Forecast | AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 100,000,000