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Income Tax - Additional Information (Detail) (USD $)
 1 Months Ended 12 Months Ended 1 Months Ended
Mar. 31, 2014
Feb. 28, 2014
Dec. 31, 2014
Dec. 31, 2013
Jan. 31, 2015
Operating Loss Carryforwards [Line Items]          
Net operating loss carryforward expire date     2019 through 2034    
Deferred tax asset, loss carryforward     $ 21,000,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwards $ 12,000,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwards  
Corporate franchise tax rate 6.50%us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate 7.10%us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate      
Decrease in accumulated deferred tax liabilities     74,000,000ed_IncreaseDecreaseInDeferredTaxLiabilities    
Decrease in regulatory asset     11,000,000ed_IncreaseDecreaseInRegulatoryAssets    
Increase in regulatory liability     62,000,000us-gaap_IncreaseDecreaseInRegulatoryLiabilities    
Expired depreciation bonus percentage       50.00%ed_ExpiredDepreciationBonusPercentage  
Increase in estimated prior year liabilities     27,000,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions 253,000,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions  
Effective income tax rate reconciliation ,uncertainty of taxes     26,000,000us-gaap_IncomeTaxReconciliationTaxContingencies    
Effective income tax rate reconciliation, uncertainty net of federal taxes     17,000,000ed_IncomeTaxReconciliationTaxContingenciesNetOfFederalTaxes    
Interest charges related to uncertain tax positions       121,000,000ed_InterestChargesOnUncertainTaxPosition  
Reduced interest expenses       10,000,000ed_ReversalOfInterestAccrualRelatedToUncertainTaxPosition  
Interest charges related to uncertain tax position, LILO transaction       131,000,000ed_LeaseInLeaseOutTransactionsInterestPaid  
Amount of interest and penalties in their consolidated balance sheets     0us-gaap_IncomeTaxExaminationPenaltiesAccrued 0us-gaap_IncomeTaxExaminationPenaltiesAccrued  
Unrecognized tax benefits amount     34,000,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate    
Unrecognized tax benefits, net of federal taxes     22,000,000ed_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRateNetOfFederalTaxes    
Subsequent Event [Member]          
Operating Loss Carryforwards [Line Items]          
Income tax refund requested         224,000,000ed_IncomeTaxRefundRequested
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
CECONY [Member]          
Operating Loss Carryforwards [Line Items]          
Decrease in accumulated deferred tax liabilities     69,000,000ed_IncreaseDecreaseInDeferredTaxLiabilities
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Decrease in regulatory asset     10,000,000ed_IncreaseDecreaseInRegulatoryAssets
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Increase in regulatory liability     59,000,000us-gaap_IncreaseDecreaseInRegulatoryLiabilities
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Increase in estimated prior year liabilities     2,000,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Effective income tax rate reconciliation ,uncertainty of taxes     2,000,000us-gaap_IncomeTaxReconciliationTaxContingencies
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Effective income tax rate reconciliation, uncertainty net of federal taxes     1,000,000ed_IncomeTaxReconciliationTaxContingenciesNetOfFederalTaxes
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Unrecognized tax benefits amount     2,000,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate
/ dei_LegalEntityAxis
= ed_CeconyMember		    
Unrecognized tax benefits, net of federal taxes     1,000,000ed_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRateNetOfFederalTaxes
/ dei_LegalEntityAxis
= ed_CeconyMember		    
CECONY [Member] | Subsequent Event [Member]          
Operating Loss Carryforwards [Line Items]          
Income tax refund requested         128,000,000ed_IncomeTaxRefundRequested
/ dei_LegalEntityAxis
= ed_CeconyMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
New York City [Member]          
Operating Loss Carryforwards [Line Items]          
Deferred tax asset, valuation allowance     $ 11,000,000us-gaap_DeferredTaxAssetsValuationAllowance
/ us-gaap_IncomeTaxAuthorityAxis
= ed_NewYorkCityMember