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, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2016
Maximum | NYSPSC
Public Utilities, General Disclosures [Line Items]
Percentage of total consolidated revenues		15.00%
Percentage of debt to total consolidated debt		20.00%
CECONY | Electric
Public Utilities, General Disclosures [Line Items]
Amortization to income of net regulatory (assets) and liabilities			$ 123,000,000
Retention of annual transmission congestion revenues								$ 90,000,000
Actual earnings adjustment mechanism incentives		$ 13,000,000
Deferred revenues	$ 101,000,000	45,000,000	101,000,000	$ 98,000,000	$ 146,000,000			101,000,000
Negative revenue adjustments		0	0	0	5,000,000
Cost reconciliations, deferred net regulatory liabilities	68,000,000	35,000,000	68,000,000	26,000,000	57,000,000			$ 68,000,000
Net utility plant reconciliations		400,000	9,000,000	(17,000,000)	(6,000,000)
Earnings sharing, threshold limit		$ 0	6,500,000	44,400,000	$ 0
Earnings sharing, positive adjustment			5,700,000
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]
Retention of annual transmission congestion revenues							$ 75,000,000
Other earnings incentives						$ 5,000,000
Authorized return on common equity (percent)							9.00%
Actual return on common equity (percent)							9.30%
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)
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%
Actual return on common equity (percent)								9.04%
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 | Transmission and distribution
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 16,869,000,000
CECONY | Electric | Year 1 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								89,000,000
CECONY | Electric | Year 1 | Other
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								2,034,000,000
CECONY | Electric | Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								400,000,000
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
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]
Net utility plant reconciliations							21,689,000,000
CECONY | Electric | Year 1 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							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
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%
Actual return on common equity (percent)								10.16%
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 | Transmission and distribution
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 17,401,000,000
CECONY | Electric | Year 2 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								177,000,000
CECONY | Electric | Year 2 | Other
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								2,102,000,000
CECONY | Electric | Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								400,000,000
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
Potential earnings adjustment mechanism incentives							47,000,000
Potential penalties (annually)							341,000,000
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]
Net utility plant reconciliations							22,338,000,000
CECONY | Electric | Year 2 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							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
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%
Actual return on common equity (percent)								9.66%
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 | Transmission and distribution
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								$ 17,929,000,000
CECONY | Electric | Year 3 | Storm hardening
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								268,000,000
CECONY | Electric | Year 3 | Other
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations								2,069,000,000
CECONY | Electric | Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								$ 400,000,000
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
Potential earnings adjustment mechanism incentives							64,000,000
Potential penalties (annually)							352,000,000
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]
Net utility plant reconciliations							23,002,000,000
CECONY | Electric | Year 3 | Scenario, Forecast | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations							$ 415,000,000