Derivative Instruments and Hedging Activities - Number of Derivative Contracts by Commodity Type (Detail)	9 Months Ended
	Sep. 30, 2014 Contract
Derivatives, Fair Value [Line Items]
Total Number of Contracts	1,335
CECONY [Member]
Derivatives, Fair Value [Line Items]
Total Number of Contracts	565
Electric Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	561
MWHs	13,588,195
Number of Capacity Contracts	79
MWs	5,758
Electric Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	75
MWHs	3,612,475
Number of Capacity Contracts	6
MWs	1,500
Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	695
Dths	75,092,291
Gas Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	484
Dths	69,880,000