Regulatory Matters - Other Regulatory Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Public Utilities, General Disclosures [Line Items]
Revenues from electric	$ 249
Revenues from gas	32us-gaap_RegulatedOperatingRevenueGas
Revenues from steam service	6us-gaap_RegulatedOperatingRevenueSteam
Potential refund to customers	1,675ed_PotentialRefundToCustomers
Overcharges of construction expenditures	208us-gaap_OtherConstructionCosts
Other regulatory liabilities	105ed_OtherRegulatoryLiabilities
Regulatory liabilities	187us-gaap_RegulatoryLiabilityCurrent	148us-gaap_RegulatoryLiabilityCurrent
CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Response and restoration costs	503
Capital expenditures	148
Regulatory liabilities	142	107
O&R [Member]
Public Utilities, General Disclosures [Line Items]
Response and restoration costs	91
Capital expenditures	15
Storm Damage [Member]
Public Utilities, General Disclosures [Line Items]
Number of customers interrupted electric distribution service	1,400,000
Net Unbilled Revenue Deferrals [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	$ 138	$ 133
Net Electric Deferrals [Member]
Public Utilities, General Disclosures [Line Items]
Amortization period	10 years

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Capital Expenditures

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Number Of Customers

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- Definition

Other Regulatory Liabilities

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Potential Refund To Customers

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- Definition

Other costs incurred and are directly related to construction and development services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2)

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The amount of regulated power revenues recognized during the period.

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The amount of regulated gas operating revenues recognized during the period.

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The amount of regulated steam operating revenues recognized during the period.

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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

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Discloses the amount charged against the accrued restructuring reserves, or earnings if not previously accrued, during the period for the specified type of restructuring cost.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 50

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-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.P.4(b))

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section P

-Subsection 3, 4

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