Environmental Matters - Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Remediation costs incurred	$ 10	$ 7
Insurance recoveries received
CECONY [Member]
Remediation costs incurred	7	7
Insurance recoveries received

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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