Income Tax - Additional Information (Details)	1 Months Ended			12 Months Ended
	Feb. 29, 2016 USD ($)	Jan. 31, 2016 USD ($)	Jan. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, accelerated bonus depreciation				$ 32,000,000
Valuation allowance				207,000,000
Deferred tax asset, valuation allowance				16,000,000	$ 15,000,000
Deferred tax assets, charitable contribution carryforwards				$ 6,000,000	5,000,000
Corporate franchise tax rate				6.50%		7.10%
Decrease in accumulated deferred tax liabilities				$ 74,000,000
Decrease in regulatory asset				11,000,000
Increase in regulatory liability				62,000,000
Income tax refund requested		$ 160,000,000	$ 224,000,000
Income tax refund	$ 160,000,000
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years				0	0	$ 0
Uncertain tax position from investment tax credit claim				19,000,000	1,000,000	27,000,000
Effective income tax rate reconciliation, uncertainty of taxes				35,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes				24,000,000
Change in effective tax rate upon completion of ongoing tax examinations				21,000,000
Change in effective tax rate upon completion of ongoing tax examinations, net of taxes				14,000,000
Unrecognized tax benefits that would have an impact on effective tax rate				24,000,000
Unrecognized tax benefits that would have an impact on effective tax rate, net of taxes				17,000,000
Penalties for uncertain tax positions				0	0	0
Amount of interest and penalties in their consolidated balance sheets				0	0
New York State
Operating Loss Carryforwards [Line Items]
Decrease in effective tax rate resulting from tax settlement				8,000,000
CECONY
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance				0	0
Decrease in accumulated deferred tax liabilities				69,000,000
Decrease in regulatory asset				10,000,000
Increase in regulatory liability				59,000,000
Income tax refund requested			$ 128,000,000
Income tax refund	$ 143,000,000
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years				0	0	0
Uncertain tax position from investment tax credit claim				19,000,000	0	$ 2,000,000
Effective income tax rate reconciliation, uncertainty of taxes				17,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes				12,000,000
Change in effective tax rate upon completion of ongoing tax examinations				2,000,000
Unrecognized tax benefits that would have an impact on effective tax rate				3,000,000
CECONY | New York State
Operating Loss Carryforwards [Line Items]
Decrease in effective tax rate resulting from tax settlement				2,000,000
Charitable Contribution
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance					$ 3,000,000
General Business Tax Credit
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards				31,000,000
Renewable Energy Tax Credits
Operating Loss Carryforwards [Line Items]
Valuation allowance				498,000,000
Tax credit carryforward, valuation allowance				0
Charitable Contribution
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, valuation allowance				0
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards				204,000,000
Federal | Carryback to 2007 and 2014
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards				178,000,000
Federal | Year 2036
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards				26,000,000
New York City
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance				12,000,000
State
Operating Loss Carryforwards [Line Items]
Deferred tax asset, valuation allowance				$ 4,000,000
State | New York State
Operating Loss Carryforwards [Line Items]
Number of claims settled | claim				2
Decrease in uncertain tax positions resulting from settlement of claims filed in previous years				$ 11,000,000
Decrease in effective tax rate resulting from tax settlement, net of taxes				5,000,000
Uncertain tax position from investment tax credit claim				21,000,000
State | CECONY | New York State
Operating Loss Carryforwards [Line Items]
Decrease in effective tax rate resulting from tax settlement, net of taxes				$ 1,000,000