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Capitalization - Carrying Amounts and Fair Values of Long-Term Debt (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Carrying Amount $ 12,191us-gaap_LongTermDebt $ 10,974us-gaap_LongTermDebt
Fair Value 13,998us-gaap_LongTermDebtFairValue 12,082us-gaap_LongTermDebtFairValue
CECONY [Member]    
Debt Instrument [Line Items]    
Carrying Amount 11,214us-gaap_LongTermDebt
/ dei_LegalEntityAxis
= ed_CeconyMember		 [1] 9,841us-gaap_LongTermDebt
/ dei_LegalEntityAxis
= ed_CeconyMember		 [1]
Fair Value $ 12,846us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= ed_CeconyMember		 $ 10,797us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= ed_CeconyMember
[1] Rates are to be reset weekly or by auction held every 35 days; December 31, 2014 rates shown.