Derivative Instruments and Hedging Activities - Number of Derivative Contracts by Commodity Type (Detail)	6 Months Ended
	Jun. 30, 2014 Contract
Derivatives, Fair Value [Line Items]
Total Number of Contracts	1,285
CECONY [Member]
Derivatives, Fair Value [Line Items]
Total Number of Contracts	576
Electric Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	557
MWHs	14,772,012
Number of Capacity Contracts	65
MWs	5,430
Electric Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	88
MWHs	3,500,475
Number of Capacity Contracts	4
MWs	600
Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	663
Dths	73,289,826
Gas Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	484
Dths	64,760,000