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Stock-Based Compensation - Stock-Based Compensation Expense (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 29ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax $ 27ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax $ 19ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
Income tax benefit 12us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 11us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 8us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Performance-Based Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 22ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember		 20ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember		 14ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember
Time-Based Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_TimeBasedRestrictedStockMember		 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_TimeBasedRestrictedStockMember		 1ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_TimeBasedRestrictedStockMember
Non-Employee Director Deferred Stock Compensation [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_NonEmployeeDirectorStockCompensationMember		 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_NonEmployeeDirectorStockCompensationMember		 1ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_NonEmployeeDirectorStockCompensationMember
Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 3ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember		 3ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember		 3ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
CECONY [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 26ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ dei_LegalEntityAxis
= ed_CeconyMember		 25ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ dei_LegalEntityAxis
= ed_CeconyMember		 18ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ dei_LegalEntityAxis
= ed_CeconyMember
Income tax benefit 10us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ dei_LegalEntityAxis
= ed_CeconyMember		 10us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ dei_LegalEntityAxis
= ed_CeconyMember		 7us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Performance-Based Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 19ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 18ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 13ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Time-Based Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_TimeBasedRestrictedStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_TimeBasedRestrictedStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 1ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_TimeBasedRestrictedStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Non-Employee Director Deferred Stock Compensation [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_NonEmployeeDirectorStockCompensationMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 2ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_NonEmployeeDirectorStockCompensationMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 1ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= ed_NonEmployeeDirectorStockCompensationMember
/ dei_LegalEntityAxis
= ed_CeconyMember
CECONY [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 3ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 $ 3ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember		 $ 3ed_ShareBasedCompensationArrangementByShareBasedPaymentAwardCompensationCostNetOfIncomeTax
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockMember
/ dei_LegalEntityAxis
= ed_CeconyMember