Environmental Matters - Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accrued Environmental Remediation Costs [Line Items]
Remediation costs incurred	$ 14	$ 8	$ 24	$ 15
Insurance recoveries received
CECONY [Member]
Accrued Environmental Remediation Costs [Line Items]
Remediation costs incurred	13	7	20	14
Insurance recoveries received