Derivative Instruments and Hedging Activities - Number of Derivative Contracts by Commodity Type (Detail)	3 Months Ended
	Mar. 31, 2014 Contract
Derivatives, Fair Value [Line Items]
Total Number of Contracts	1,165
CECONY [Member]
Derivatives, Fair Value [Line Items]
Total Number of Contracts	538
Electric Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	548
MWHs	14,882,496
Number of Capacity Contracts	67
MWs	6,442
Electric Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	87
MWHs	3,198,875
Number of Capacity Contracts	4
MWs	1,200
Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	550
Dths	70,343,157
Gas Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	447
Dths	64,560,000