Derivative Instruments and Hedging Activities - Number of Derivative Contracts by Commodity Type (Detail)	9 Months Ended
	Sep. 30, 2013 Contract
Derivatives, Fair Value [Line Items]
Number of Capacity Contracts	1,187
CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Capacity Contracts	628
Electric Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	470
MWHs	13,643,994
Number of Capacity Contracts	83
MWs	11,625
Electric Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	82
MWHs	3,127,600
Number of Capacity Contracts	4
MWs	1,200
Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	634
Dths	79,090,035
Number of Capacity Contracts	1,187
Gas Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	542
Dths	75,470,000
Number of Capacity Contracts	628