Income Tax - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 29, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Decrease in net deferred tax liabilities resulting from TCJA		$ 5,312,000,000
Change in net income resulting from TCJA		259,000,000
Operating loss carryforwards, accelerated bonus depreciation		19,000,000
Deferred tax asset, valuation allowance		33,000,000	$ 16,000,000
Deferred tax assets, charitable contribution carryforwards		4,000,000	5,000,000	$ 5,000,000
Income tax refund	$ 160,000,000
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years		6,000,000	0	0
Effective income tax rate reconciliation, uncertainty of taxes		8,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes		7,000,000
Penalties for uncertain tax positions		0	0	0
Amount of interest and penalties in their consolidated balance sheets		0	0
Unrecognized tax benefits that would have an impact on effective tax rate		12,000,000
Unrecognized tax benefits that would have an impact on effective tax rate, net of taxes		11,000,000
Charitable Contribution
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance				3,000,000
New York State
Operating Loss Carryforwards [Line Items]
Decrease in effective tax rate resulting from tax settlement		6,000,000
General Business Tax Credit
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		176,000,000
Renewable Energy Tax Credits
Operating Loss Carryforwards [Line Items]
Valuation allowance		658,000,000
Tax credit carryforward, valuation allowance		0
Charitable Contribution
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, valuation allowance		0	0	0
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		121,000,000
Federal | Carryback to 2007 and 2014
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		53,000,000
Federal | Year 2036
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		68,000,000
State
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance		12,000,000
State | New York State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		137,000,000
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years		30,000,000
Decrease in effective tax rate resulting from tax settlement, net of taxes		4,000,000
New York City
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance		21,000,000
Parent Company
Operating Loss Carryforwards [Line Items]
Change in net income resulting from TCJA		(21,000,000)
Clean Energy Businesses
Operating Loss Carryforwards [Line Items]
Change in net income resulting from TCJA		269,000,000
Con Edison Transmission
Operating Loss Carryforwards [Line Items]
Change in net income resulting from TCJA		11,000,000
Future Income Tax
Operating Loss Carryforwards [Line Items]
Increase in regulatory liability resulting from TCJA		3,713,000,000
Accelerated Tax Depreciation Benefits
Operating Loss Carryforwards [Line Items]
Increase in regulatory liability resulting from TCJA		2,684,000,000
Future Income Tax
Operating Loss Carryforwards [Line Items]
Decrease in regulatory asset resulting from TCJA		1,250,000,000
Revenue Taxes
Operating Loss Carryforwards [Line Items]
Decrease in regulatory asset resulting from TCJA		90,000,000
CECONY
Operating Loss Carryforwards [Line Items]
Decrease in net deferred tax liabilities resulting from TCJA		4,781,000,000
Deferred tax asset, valuation allowance		0	0
Income tax refund	$ 143,000,000
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years		0	$ 0	$ 0
Effective income tax rate reconciliation, uncertainty of taxes		4,000,000
Unrecognized tax benefits that would have an impact on effective tax rate		5,000,000
CECONY | New York State
Operating Loss Carryforwards [Line Items]
Decrease in effective tax rate resulting from tax settlement		18,000,000
CECONY | State | New York State
Operating Loss Carryforwards [Line Items]
Decrease in effective tax rate resulting from tax settlement, net of taxes		12,000,000
CECONY | Future Income Tax
Operating Loss Carryforwards [Line Items]
Increase in regulatory liability resulting from TCJA		3,513,000,000
CECONY | Accelerated Tax Depreciation Benefits
Operating Loss Carryforwards [Line Items]
Increase in regulatory liability resulting from TCJA		2,542,000,000
CECONY | Future Income Tax
Operating Loss Carryforwards [Line Items]
Decrease in regulatory asset resulting from TCJA		1,182,000,000
CECONY | Revenue Taxes
Operating Loss Carryforwards [Line Items]
Decrease in regulatory asset resulting from TCJA		$ 86,000,000