Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Asbestos suits [Member]	Mar. 31, 2012 Asbestos suits [Member]	Mar. 31, 2013 Workers' compensation [Member]	Mar. 31, 2012 Workers' compensation [Member]	Mar. 31, 2013 CECONY [Member]	Dec. 31, 2012 CECONY [Member]	Mar. 31, 2013 CECONY [Member] Asbestos suits [Member]	Mar. 31, 2012 CECONY [Member] Asbestos suits [Member]	Mar. 31, 2013 CECONY [Member] Workers' compensation [Member]	Mar. 31, 2012 CECONY [Member] Workers' compensation [Member]
Site Contingency [Line Items]
Accrued liability			$ 10	$ 10	$ 95	$ 94			$ 10	$ 10	$ 90	$ 89
Regulatory assets	$ 9,516	$ 9,779	$ 10	$ 10	$ 20	$ 19	$ 8,802	$ 9,032	$ 10	$ 10	$ 20	$ 19

Total costs accrued as of the balance sheet date for environmental loss contingencies.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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