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Pension Benefits - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Pension Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected contributions $ 750us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
CECONY [Member] | Pension Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected contributions 697us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= ed_CeconyMember
Contributions 204us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Non-qualified Supplemental Plan [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected contributions $ 16us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
/ dei_LegalEntityAxis
= ed_CeconyMember