Environmental Matters - Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Remediation costs incurred	$ 31	$ 39
Insurance recoveries received*	4
CECONY [Member]
Remediation costs incurred	26	35
Insurance recoveries received*	$ 4

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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