Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Con Edison [Member]
Site Contingency [Line Items]
Regulatory assets	$ 8,974	$ 9,501
Con Edison [Member] | Asbestos Suits [Member]
Site Contingency [Line Items]
Accrued liability	10	10
Regulatory assets	10	10
Con Edison [Member] | Workers' Compensation [Member]
Site Contingency [Line Items]
Accrued liability	94	98
Regulatory assets	19	23
CECONY [Member]
Site Contingency [Line Items]
Regulatory assets	8,347	8,801
CECONY [Member] | Asbestos Suits [Member]
Site Contingency [Line Items]
Accrued liability	10	10
Regulatory assets	10	10
CECONY [Member] | Workers' Compensation [Member]
Site Contingency [Line Items]
Accrued liability	89	93
Regulatory assets	$ 19	$ 23