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Capitalization - Carrying Amounts and Fair Values of Long-Term Debt (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Carrying Amount $ 10,977 $ 10,768
Fair Value 12,313 12,935
CECONY [Member]
   
Carrying Amount 9,840 9,845
Fair Value $ 10,991 $ 11,751