Environmental Matters - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Site Contingency [Line Items]
Remediation cost estimate	$ 29,000,000	$ 41,000,000
Asbestos Proceedings [Member]
Site Contingency [Line Items]
Estimated undiscounted asbestos liability	8,000,000
Superfund Sites [Member]
Site Contingency [Line Items]
Remediation cost estimate	39,000,000
Superfund Sites [Member] | Manufactured Gas Plant Sites [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants	2,700,000,000
CECONY [Member]
Site Contingency [Line Items]
Remediation cost estimate	20,000,000	35,000,000
CECONY [Member] | Asbestos Proceedings [Member]
Site Contingency [Line Items]
Estimated undiscounted asbestos liability	7,000,000
Estimated undiscounted asbestos liability in year	15 years
CECONY [Member] | Superfund Sites [Member]
Site Contingency [Line Items]
Remediation cost estimate	35,000,000
CECONY [Member] | Superfund Sites [Member] | Manufactured Gas Plant Sites [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants	$ 2,500,000,000