Environmental Matters - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Asbestos Proceedings [Member]
Site Contingency [Line Items]
Estimated undiscounted asbestos liability	$ 8,000,000
Estimated undiscounted asbestos liability in year	15 years
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] | Asbestos Proceedings [Member]
Site Contingency [Line Items]
Estimated undiscounted asbestos liability	7,000,000
Estimated undiscounted asbestos liability in year	15 years
CECONY [Member] | Manufactured Gas Plant Sites [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants		$ 2,500,000,000