Regulatory Matters - Summary of Utilities Rate Plans (CECONY-Electric) (Details) - USD ($)	1 Months Ended	12 Months Ended			36 Months Ended
	Dec. 31, 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	$ 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	940,000,000	899,000,000			940,000,000
CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Deferred revenues	101,000,000	101,000,000	98,000,000	$ 146,000,000		101,000,000
Negative revenue adjustments		0	0	5,000,000
Cost reconciliations, deferred net regulatory liabilities	68,000,000	68,000,000	26,000,000	57,000,000		$ 68,000,000
Deferred regulatory asset		9,000,000	17,000,000	6,000,000
Earnings sharing, threshold limit		6,500,000	44,400,000	$ 0
Common equity ratio (percent)						48.00%
Base rate change deferral regulatory liability impact	0	$ 0	$ 30,000,000			$ 0
Increase in gas base rate due to expiration of temporary credit under the prior rate plan	$ 48,000,000
Deferrals for property taxes limitation from rates (percent)		90.00%
Recovery deferral (percentage)	80.00%	80.00%				80.00%
Maximum deferral (percentage)	30.00%	30.00%				30.00%
CECONY | Electric | Deferred storm costs
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory asset		$ 107,000,000
Decrease in recoverable property damage costs		4,000,000
CECONY | Electric | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Amortization to income of net regulatory (assets) and liabilities		123,000,000
Authorized return on common equity (percent)					9.00%
Earnings sharing (percentage)					9.50%
Common equity ratio (percent)					48.00%
Recovery or refund of energy costs, deferral period					10 years
CECONY | Electric | Scenario, Forecast | NYSPSC
Public Utilities, General Disclosures [Line Items]
Base rate changes					$ 199,000,000
CECONY | Electric | Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes	$ (76,200,000)	$ (76,200,000)				$ (76,200,000)
Amortization to income of net regulatory (assets) and liabilities						(37,000,000)
Retention of annual transmission congestion revenues						90,000,000
Average rate base						$ 17,323,000,000
Weighted average cost of capital (after-tax) (percent)						7.05%
Authorized return on common equity (percent)						9.20%
Earnings sharing (percentage)	9.80%	9.80%				9.80%
Cost of long-term debt (percent)	5.17%	5.17%				5.17%
Deferral, annual maximum (not more than) (percent)		0.05%
CECONY | Electric | Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)						$ 400,000,000
CECONY | Electric | Year 1 | Transmission and distribution
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						16,869,000,000
CECONY | Electric | Year 1 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						89,000,000
CECONY | Electric | Year 1 | Other
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						2,034,000,000
CECONY | Electric | Year 1 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes					195,000,000
Amortization to income of net regulatory (assets) and liabilities					84,000,000
Retention of annual transmission congestion revenues					75,000,000
Potential earnings adjustment mechanism incentives					28,000,000
Potential penalties (annually)					376,000,000
Average rate base					$ 18,902,000,000
Weighted average cost of capital (after-tax) (percent)					6.82%
Cost of long-term debt (percent)					4.93%
Recovery of energy efficiency and savings program costs					$ 20,500,000
CECONY | Electric | Year 1 | Scenario, Forecast | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset					21,689,000,000
CECONY | Electric | Year 1 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset					126,000,000
CECONY | Electric | Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes	$ 124,000,000	$ 124,000,000				124,000,000
Amortization to income of net regulatory (assets) and liabilities						(37,000,000)
Retention of annual transmission congestion revenues						90,000,000
Average rate base						$ 18,113,000,000
Weighted average cost of capital (after-tax) (percent)						7.08%
Authorized return on common equity (percent)						9.20%
Earnings sharing (percentage)	9.80%	9.80%				9.80%
Cost of long-term debt (percent)	5.23%	5.23%				5.23%
Deferral, annual maximum (not more than) (percent)		0.075%
CECONY | Electric | Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)						$ 400,000,000
CECONY | Electric | Year 2 | Transmission and distribution
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						17,401,000,000
CECONY | Electric | Year 2 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						177,000,000
CECONY | Electric | Year 2 | Other
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						2,102,000,000
CECONY | Electric | Year 2 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes					155,000,000
Amortization to income of net regulatory (assets) and liabilities					83,000,000
Retention of annual transmission congestion revenues					75,000,000
Potential earnings adjustment mechanism incentives					47,000,000
Potential penalties (annually)					383,000,000
Average rate base					$ 19,530,000,000
Weighted average cost of capital (after-tax) (percent)					6.80%
Cost of long-term debt (percent)					4.88%
Recovery of energy efficiency and savings program costs					$ 49,000,000
CECONY | Electric | Year 2 | Scenario, Forecast | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset					22,338,000,000
CECONY | Electric | Year 2 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset					257,000,000
CECONY | Electric | Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes	$ 0	$ 0				0
Amortization to income of net regulatory (assets) and liabilities						123,000,000
Retention of annual transmission congestion revenues						90,000,000
Average rate base						$ 18,282,000,000
Weighted average cost of capital (after-tax) (percent)						6.91%
Authorized return on common equity (percent)						9.00%
Earnings sharing (percentage)	9.60%	9.60%				9.60%
Cost of long-term debt (percent)	5.09%	5.09%				5.09%
Deferral, annual maximum (not more than) (percent)		0.10%
CECONY | Electric | Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)						$ 400,000,000
CECONY | Electric | Year 3 | Transmission and distribution
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						17,929,000,000
CECONY | Electric | Year 3 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						268,000,000
CECONY | Electric | Year 3 | Other
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset						$ 2,069,000,000
CECONY | Electric | Year 3 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes					155,000,000
Amortization to income of net regulatory (assets) and liabilities					69,000,000
Retention of annual transmission congestion revenues					75,000,000
Potential earnings adjustment mechanism incentives					64,000,000
Potential penalties (annually)					395,000,000
Average rate base					$ 20,277,000,000
Weighted average cost of capital (after-tax) (percent)					6.73%
Cost of long-term debt (percent)					4.74%
Recovery of energy efficiency and savings program costs					$ 107,500,000
CECONY | Electric | Year 3 | Scenario, Forecast | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset					23,002,000,000
CECONY | Electric | Year 3 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Deferred regulatory asset					$ 415,000,000