Derivative Instruments and Hedging Activities - Number of Derivative Contracts by Commodity Type (Detail)	6 Months Ended
	Jun. 30, 2013 Contract
Derivatives, Fair Value [Line Items]
Number of Capacity Contracts	1,188
CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Capacity Contracts	620
Electric Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	498
MWHs	15,234,227
Number of Capacity Contracts	72
MWs	11,712
Electric Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	91
MWHs	3,674,400
Number of Capacity Contracts
MWs
Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	618
Dths	81,575,092
Number of Capacity Contracts	1,188
Gas Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Energy Contracts	529
Dths	76,570,000
Number of Capacity Contracts	620