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Pension Benefits - Schedule of Employer Contribution to Defined Savings Plan (Detail) (Pension Benefits [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]      
Employer contribution to the defined savings plan $ 32ed_DefinedContributionEmployerContributions $ 30ed_DefinedContributionEmployerContributions $ 23ed_DefinedContributionEmployerContributions
CECONY [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Employer contribution to the defined savings plan $ 27ed_DefinedContributionEmployerContributions
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 $ 26ed_DefinedContributionEmployerContributions
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 $ 21ed_DefinedContributionEmployerContributions
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= ed_CeconyMember