Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Gas) (Details) - USD ($)	9 Months Ended	12 Months Ended			36 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2019	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Cost reconciliations, deferred net regulatory liabilities		$ 986,000,000	$ 947,000,000			$ 986,000,000
CECONY
Public Utilities, General Disclosures [Line Items]
Cost reconciliations, deferred net regulatory liabilities		940,000,000	899,000,000			940,000,000
CECONY | Gas
Public Utilities, General Disclosures [Line Items]
Amount of revenues retained		65,000,000	66,000,000	$ 70,000,000		$ 65,000,000
Percentage of revenue reserve						15.00%
Deferred revenues		71,000,000	54,000,000	28,000,000		$ 71,000,000
Potential penalties (annually)		56,000,000	44,000,000	33,000,000
Negative revenue adjustments		0	0	0
Cost reconciliations, deferred net regulatory liabilities		$ 32,000,000	11,000,000	38,000,000		$ 32,000,000
Net utility plant reconciliations			1,000,000
Earnings sharing (percentage)		9.90%				9.90%
Earnings sharing, threshold limit		$ 0	$ 0	$ 0
Common equity ratio (percent)						48.00%
Base rate change deferral regulatory liability impact		$ 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%
Deferral, annual maximum (not more than) (percent)		0.10%
CECONY | Gas | Maximum
Public Utilities, General Disclosures [Line Items]
Amount of revenues retained		$ 65,000,000				65,000,000
CECONY | Gas | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Percentage of revenue reserve					15.00%
Earnings sharing (percentage)					9.50%
Common equity ratio (percent)					48.00%
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)
Amortization to income of net regulatory (assets) and liabilities						4,000,000
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%
Cost of long-term debt (percent)		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%
Cost of long-term debt (percent)					4.93%
CECONY | Gas | Year 1 | Scenario, Forecast | Gas excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 5,844,000,000
CECONY | Gas | Year 1 | Scenario, Forecast | Advanced metering infrastructure (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
Amortization to income of net regulatory (assets) and liabilities						4,000,000
Average rate base						$ 3,863,000,000
Weighted average cost of capital (after-tax) (percent)						7.13%
Cost of long-term debt (percent)		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)					75,000,000
Average rate base					$ 5,395,000,000
Weighted average cost of capital (after-tax) (percent)					6.80%
Cost of long-term debt (percent)					4.88%
CECONY | Gas | Year 2 | Scenario, Forecast | Gas excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 6,512,000,000
CECONY | Gas | Year 2 | Scenario, Forecast | Advanced metering infrastructure (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
Amortization to income of net regulatory (assets) and liabilities						4,000,000
Average rate base						$ 4,236,000,000
Weighted average cost of capital (after-tax) (percent)						7.21%
Cost of long-term debt (percent)		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)					83,000,000
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 excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 7,177,000,000
CECONY | Gas | Year 3 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 100,000,000