Income Tax - Income Tax Reconciliation (Details)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
STATUTORY TAX RATE
Federal	21.00%	21.00%
Changes in computed taxes resulting from:
State income tax	4.00%	4.00%
Amortization of excess deferred federal income taxes	(9.00%)	(9.00%)
Taxes attributable to non-controlling interests	0.00%	(1.00%)
Cost of removal	2.00%	2.00%
Other plant-related items	(1.00%)	(1.00%)
Renewable energy credits	(1.00%)	(2.00%)
CARES Act NOL carryback	0.00%	(1.00%)
Other	0.00%	(1.00%)
Effective tax rate	16.00%	12.00%
CECONY
STATUTORY TAX RATE
Federal	21.00%	21.00%
Changes in computed taxes resulting from:
State income tax	5.00%	5.00%
Amortization of excess deferred federal income taxes	(7.00%)	(8.00%)
Taxes attributable to non-controlling interests	0.00%	0.00%
Cost of removal	1.00%	2.00%
Other plant-related items	0.00%	(1.00%)
Renewable energy credits	0.00%	0.00%
CARES Act NOL carryback	0.00%	0.00%
Other	0.00%	0.00%
Effective tax rate	20.00%	19.00%

Effective Income Tax Rate Reconciliation, CARES Act NOL Carryback, Percent

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Effective Income Tax Rate Reconciliation, cost of removal

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Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amortization Of Excess Deferred Federal 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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