Income Tax - Schedule of Income Tax Reconciliation (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
STATUTORY TAX RATE
Federal	21.00%	21.00%	21.00%
Changes in computed taxes resulting from:
State income taxes, net of federal income tax benefit	4.00%	4.00%	4.00%
Taxes attributable to noncontrolling interests	(1.00%)	(1.00%)	0.00%
Cost of removal	2.00%	1.00%	1.00%
Other plant-related items	(1.00%)	(1.00%)	(1.00%)
TCJA deferred tax re-measurement	0	0	0.02
Amortization of excess deferred federal income taxes	(14.00%)	(4.00%)	(3.00%)
Renewable energy credits	(3.00%)	(2.00%)	(1.00%)
Research and development credits	0.00%	(1.00%)	0.00%
Other	(1.00%)	0.00%	0.00%
Effective tax rate	7.00%	17.00%	23.00%
CECONY
STATUTORY TAX RATE
Federal	21.00%	21.00%	21.00%
Changes in computed taxes resulting from:
State income taxes, net of federal income tax benefit	5.00%	5.00%	5.00%
Taxes attributable to noncontrolling interests	0.00%	0.00%	0.00%
Cost of removal	1.00%	1.00%	1.00%
Other plant-related items	(1.00%)	(1.00%)	(1.00%)
TCJA deferred tax re-measurement	0	0	0
Amortization of excess deferred federal income taxes	(12.00%)	(4.00%)	(3.00%)
Renewable energy credits	0.00%	0.00%	0.00%
Research and development credits	0.00%	(1.00%)	(1.00%)
Other	1.00%	0.00%	(1.00%)
Effective tax rate	15.00%	21.00%	21.00%

Effective Income Tax Rate Reconciliation, cost of removal

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Effective Income Tax Rate Reconciliation, Deductible Expense Amortization Of Excess Deferred Income Taxes, Percent

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Effective Income Tax Rate Reconciliation, Other Plant-Related Items, Percent

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Effective Income Tax Rate Reconciliation, Tax Credit, Renewable Energy Credits, Percent

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Federal Statutory Income Tax Rate [Abstract]

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to noncontrolling interest income (loss) exempt from income taxes.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of reported income tax expense (benefit) in excess of (less than) expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operations, attributable to Tax Cuts and Jobs Act.

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