Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Site Contingency [Line Items]
Regulatory assets	$ 9,779	$ 9,595
Asbestos suits [Member]
Site Contingency [Line Items]
Accrued liability	10	10
Regulatory assets	10	10
Workers' compensation [Member]
Site Contingency [Line Items]
Accrued liability	94	98
Regulatory assets	19	23
CECONY [Member]
Site Contingency [Line Items]
Regulatory assets	9,032	8,890
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