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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+ Details

Environmental Matters - Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Con Edison [Member]
Site Contingency [Line Items]
Remediation costs incurred	$ 3	$ 9	$ 18	$ 24
Insurance recoveries received
CECONY [Member]
Site Contingency [Line Items]
Remediation costs incurred	1	9	15	22
Insurance recoveries received