Derivative Instruments and Hedging Activities - Aggregate Fair Value of All Derivative Instruments with Credit-Risk-Related Contingent Features (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Derivatives, Fair Value [Line Items]
Collateral posted
Additional Collateral Aggregate Fair Value Down below Investment Grade [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	64
Additional Collateral Required Due To Loss Of Unsecured Credit [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	29
CECONY [Member]
Derivatives, Fair Value [Line Items]
Collateral posted
CECONY [Member] | Additional Collateral Aggregate Fair Value Down below Investment Grade [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	1
CECONY [Member] | Additional Collateral Required Due To Loss Of Unsecured Credit [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	$ 7