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Capitalization - Carrying Amounts and Fair Values of Long-Term Debt (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Carrying Amount $ 11,195 $ 10,974
Fair Value 12,696 12,082
CECONY [Member]
   
Debt Instrument [Line Items]    
Carrying Amount 10,216 9,841
Fair Value $ 11,537 $ 10,797