Environmental Matters - Accrued Liability for Asbestos Suits and Workers' Compensation Proceedings (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Site Contingency [Line Items]
Regulatory assets	$ 7,230	$ 9,779
Asbestos Suits [Member]
Site Contingency [Line Items]
Accrued liability	8	10
Regulatory assets	8	10
Workers Compensation Insurance [Member]
Site Contingency [Line Items]
Accrued liability	87	94
Regulatory assets	12	19
CECONY [Member]
Site Contingency [Line Items]
Regulatory assets	6,665	9,032
CECONY [Member] | Asbestos Suits [Member]
Site Contingency [Line Items]
Accrued liability	7	10
Regulatory assets	7	10
CECONY [Member] | Workers Compensation Insurance [Member]
Site Contingency [Line Items]
Accrued liability	82	89
Regulatory assets	$ 12	$ 19