Derivative Instruments And Hedging Activities - Number Of Derivative Contracts By Commodity Type (Detail)	9 Months Ended
	Sep. 30, 2012 Contract MWh MW
Description Of Derivative Activity Volume Electric Derivatives [Member] | Con Edison [Member]
Derivatives, Fair Value [Line Items]
Number of Contracts	576	[1]
MWhs	12,807,613	[2]
Number of Capacity Contracts	78	[1]
MW-Months	10,019	[2]
Description Of Derivative Activity Volume Electric Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Contracts	113	[1]
MWhs	3,271,000	[2]
Description Of Derivative Activity Volume Gas Derivatives [Member] | Con Edison [Member]
Derivatives, Fair Value [Line Items]
Number of Contracts	635	[1]
Dths	86,541,700	[2]
Number of Capacity Contracts	1,289	[1]
Description Of Derivative Activity Volume Gas Derivatives [Member] | CECONY [Member]
Derivatives, Fair Value [Line Items]
Number of Contracts	515	[1]
Dths	81,080,000	[2]
Number of Capacity Contracts	628	[1]

[1] Qualifying derivative contracts, which have been designated as normal purchases or normal sales contracts, are not reported at fair value under the accounting rules for derivatives and hedging and, therefore, are excluded from the table.

[2] Volumes are reported net of long and short positions.