Regulatory Matters - Other Regulatory Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Public Utilities, General Disclosures [Line Items]
Revenues from electric		$ 249
Revenues from gas		32
Revenues from steam service		6
Potential refund to customers		1,462
Overcharges of construction expenditures	208	208
Regulatory liability	38	38
Company recovered from related parties	16	16
Amount recovered for the benefit of customers	15
Additional refundable amounts applicable to customers	25
Regulatory asset	7,090	7,090	7,230
CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Response and restoration costs		490
Capital expenditures		149
Regulatory asset	6,527	6,527	6,665
O&R [Member]
Public Utilities, General Disclosures [Line Items]
Response and restoration costs		93
Capital expenditures		15
Storm Costs [Member] | Rockland Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset	$ 27	$ 27
Storm Damage [Member]
Public Utilities, General Disclosures [Line Items]
Number of customers interrupted electric distribution service		1,400,000