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	Jun. 30, 2014
Additional Collateral Aggregate Fair Value Down below Investment Grade [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	$ 45
Additional Collateral Aggregate Fair Value Down below Investment Grade [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	1
Additional Collateral Required Due To Loss Of Unsecured Credit [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	17
Additional Collateral Required Due To Loss Of Unsecured Credit [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Collateral posted	$ 5