Regulatory Matters - Other Regulatory Matters - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Regulatory Assets And Liabilities [Line Items]
Revenue from electric	$ 249,000,000
Revenue from gas	32,000,000
Revenue from steam service	6,000,000
Potential refund from customers	1,103
Overcharges of construction expenditures	208,000,000
Regulatory liability	14,000,000
Regulatory liabilities	183,000,000	118,000,000
Storm Damage [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Number of customers Interrupted electric distribution service	1,400,000
Net unbilled revenue deferrals [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities	136,000,000
CECONY [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Response and restoration costs	363,000,000
Capital expenditure	104,000,000
Regulatory liabilities	145,000,000	79,000,000
O & R [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Response and restoration costs	98,000,000
Capital expenditure	$ 14,000,000