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Derivative Instruments and Hedging Activities - Hedged Volume of Derivative Transactions (Detail)
 12 Months Ended
Dec. 31, 2014
MWh
Electric Energy Derivative [Member]  
Derivatives, Fair Value [Line Items]  
MWHs 17,792,555ed_Mwhs
/ us-gaap_DerivativeInstrumentRiskAxis
= ed_ElectricEnergyDerivativeMember
Electric Capacity Derivative [Member]  
Derivatives, Fair Value [Line Items]  
MWs 7,706ed_Mws
/ us-gaap_DerivativeInstrumentRiskAxis
= ed_ElectricCapacityDerivativeMember
Natural Gas Derivative [Member]  
Derivatives, Fair Value [Line Items]  
Dths 66,793,011ed_Dths
/ us-gaap_DerivativeInstrumentRiskAxis
= ed_NaturalGasDerivativeMember
CECONY [Member] | Electric Energy Derivative [Member]  
Derivatives, Fair Value [Line Items]  
MWHs 5,543,250ed_Mwhs
/ us-gaap_DerivativeInstrumentRiskAxis
= ed_ElectricEnergyDerivativeMember
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Electric Capacity Derivative [Member]  
Derivatives, Fair Value [Line Items]  
MWs 2,100ed_Mws
/ us-gaap_DerivativeInstrumentRiskAxis
= ed_ElectricCapacityDerivativeMember
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Natural Gas Derivative [Member]  
Derivatives, Fair Value [Line Items]  
Dths 62,065,000ed_Dths
/ us-gaap_DerivativeInstrumentRiskAxis
= ed_NaturalGasDerivativeMember
/ dei_LegalEntityAxis
= ed_CeconyMember