Income Tax - Schedule of Income Tax Reconciliation (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
STATUTORY TAX RATE
Federal	35.00%	35.00%	35.00%
Changes in computed taxes resulting from:
State income tax	4.00%	4.00%	5.00%
Cost of removal	1.00%	(1.00%)	(5.00%)
Other plant-related items	(1.00%)	0.00%	0.00%
TCJA tax rate reduction	(13.00%)	0.00%	0.00%
Renewable energy credits	(1.00%)	(1.00%)	(1.00%)
Research and development credits	(0.00%)	(1.00%)	(0.00%)
Other	(2.00%)	0.00%	0.00%
Effective tax rate	23.00%	36.00%	34.00%
CECONY
STATUTORY TAX RATE
Federal	35.00%	35.00%	35.00%
Changes in computed taxes resulting from:
State income tax	4.00%	4.00%	5.00%
Cost of removal	1.00%	(1.00%)	(5.00%)
Other plant-related items	(1.00%)	(1.00%)	0.00%
TCJA tax rate reduction	0.00%	0.00%	0.00%
Renewable energy credits	(0.00%)	(0.00%)	(0.00%)
Research and development credits	(0.00%)	(1.00%)	(0.00%)
Other	(1.00%)	0.00%	0.00%
Effective tax rate	38.00%	36.00%	35.00%

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

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Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, 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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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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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