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Capitalization - Carrying Amounts and Fair Values of Long-Term Debt (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Carrying Amount $ 10,768 $ 10,673
Fair Value 12,935 12,744
CECONY [Member]
   
Carrying Amount 9,845 9,745
Fair Value $ 11,751 $ 11,593