Environmental Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2010
CECONY [Member] | Asbestos Proceedings [Member]
Accrued Environmental Remediation Costs [Line Items]
Estimated undiscounted asbestos liability	$ 10
Estimated undiscounted asbestos liability in year	15 years
CECONY [Member] | Superfund Sites [Member] | Environmental remediation expense [Member] | Manufactured gas plant sites [Member] | Other manufactured gas plant-related environmental contaminants [Member]
Accrued Environmental Remediation Costs [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants	1,900
O&R [Member] | Superfund Sites [Member] | Environmental remediation expense [Member] | Manufactured gas plant sites [Member]
Accrued Environmental Remediation Costs [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants	$ 200