Income Tax - Income Tax Reconciliation (Details)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
STATUTORY TAX RATE
Federal	21.00%	21.00%
Changes in computed taxes resulting from:
State income tax	5.00%	4.00%
Cost of removal	1.00%	1.00%
Other plant-related items	(1.00%)	0.00%
Renewable energy credits	(1.00%)	(1.00%)
Amortization of excess deferred federal income taxes	(4.00%)	(3.00%)
Other	(1.00%)	(1.00%)
Effective tax rate	20.00%	21.00%
CECONY
STATUTORY TAX RATE
Federal	21.00%	21.00%
Changes in computed taxes resulting from:
State income tax	6.00%	5.00%
Cost of removal	1.00%	1.00%
Other plant-related items	0.00%	(1.00%)
Renewable energy credits	(0.00%)	(0.00%)
Amortization of excess deferred federal income taxes	(4.00%)	(3.00%)
Other	(1.00%)	0.00%
Effective tax rate	23.00%	23.00%

Effective Income Tax Rate Reconciliation, cost of removal

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Effective Income Tax Rate Reconciliation, Other Plant-Related Items, 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 other adjustments.

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