Income Tax - Schedule of Differences on Deferred Tax Assets and Liabilities (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Income Tax Contingency [Line Items]
Property basis differences	$ 7,510,000,000	$ 7,012,000,000
Unrecognized pension and other postretirement costs	1,968,000,000	1,109,000,000
Regulatory asset - future income tax	910,000,000	871,000,000
Environmental remediation costs	376,000,000	381,000,000
Deferred storm costs	129,000,000ed_DeferredTaxLiabilitiesStormCosts	179,000,000ed_DeferredTaxLiabilitiesStormCosts
Equity investments	168,000,000	21,000,000
Other regulatory assets	347,000,000	402,000,000
Unamortized investment tax credits	126,000,000	43,000,000
Total deferred tax liabilities and investment tax credits	11,534,000,000us-gaap_DeferredTaxLiabilities	10,018,000,000us-gaap_DeferredTaxLiabilities
Accrued pension and other postretirement costs	1,306,000,000	458,000,000
Regulatory liabilities	615,000,000	604,000,000
Superfund and other environmental costs	306,000,000	301,000,000
Asset retirement obligations	77,000,000	58,000,000
Loss carryforwards	21,000,000	12,000,000
Loss carryforwards, valuation reserve	(11,000,000)	(12,000,000)
Other	272,000,000us-gaap_DeferredTaxAssetsOther	253,000,000us-gaap_DeferredTaxAssetsOther
Total deferred tax assets	2,586,000,000us-gaap_DeferredTaxAssetsGross	1,674,000,000us-gaap_DeferredTaxAssetsGross
Net deferred tax liabilities and investment tax credits	8,948,000,000	8,344,000,000
Deferred income taxes and investment tax credits - noncurrent	9,076,000,000ed_DeferredIncomeTaxesAndCreditsGross	8,466,000,000ed_DeferredIncomeTaxesAndCreditsGross
Deferred tax assets - current	(128,000,000)us-gaap_DeferredTaxAssetsNetCurrent	(122,000,000)us-gaap_DeferredTaxAssetsNetCurrent
Net deferred tax liabilities and investment tax credits	8,948,000,000us-gaap_DeferredTaxAssetsLiabilitiesNet	8,344,000,000us-gaap_DeferredTaxAssetsLiabilitiesNet
CECONY [Member]
Income Tax Contingency [Line Items]
Property basis differences	6,938,000,000	6,424,000,000
Unrecognized pension and other postretirement costs	1,872,000,000	1,060,000,000
Regulatory asset - future income tax	863,000,000	825,000,000
Environmental remediation costs	333,000,000	337,000,000
Deferred storm costs	91,000,000	136,000,000
Other regulatory assets	300,000,000	364,000,000
Unamortized investment tax credits	37,000,000	42,000,000
Total deferred tax liabilities and investment tax credits	10,434,000,000	9,188,000,000
Accrued pension and other postretirement costs	1,155,000,000	364,000,000
Regulatory liabilities	574,000,000	569,000,000
Superfund and other environmental costs	264,000,000	256,000,000
Asset retirement obligations	75,000,000	58,000,000
Other	203,000,000	209,000,000
Total deferred tax assets	2,271,000,000	1,456,000,000
Net deferred tax liabilities and investment tax credits	8,163,000,000	7,732,000,000
Deferred income taxes and investment tax credits - noncurrent	8,257,000,000	7,832,000,000
Deferred tax assets - current	(94,000,000)	(100,000,000)
Net deferred tax liabilities and investment tax credits	$ 8,163,000,000	$ 7,732,000,000

Deferred income taxes and credits, Gross

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Deferred Tax Assets Asset Retirement Obligations

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Deferred Tax Assets, Pension and other postretirement costs

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Deferred tax assets superfund and environmental costs.

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Deferred tax liabilities environmental redemption costs.

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Deferred tax liabilities other regulatory assets.

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Deferred Tax Liabilities Pension And Other Postretirement Costs

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Deferred tax liabilities storm costs.

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Amount of deferred income tax expense (benefit) and income tax credits.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards expected to be realized or consumed within one year or operating cycle, if longer.

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The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized.

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