Environmental Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2010
CECONY [Member] | Asbestos Proceeding [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	1,900.0
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	$ 200.0