Environmental Matters - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Asbestos Proceedings
Site Contingency [Line Items]
Estimated undiscounted asbestos liability	$ 8,000,000	$ 8,000,000
Estimated undiscounted asbestos liability in year	15 years
Manufactured gas plant sites | Maximum
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants (up to)		2,700,000,000
CECONY | Asbestos Proceedings
Site Contingency [Line Items]
Estimated undiscounted asbestos liability	$ 7,000,000	7,000,000
Estimated undiscounted asbestos liability in year	15 years
CECONY | Manufactured gas plant sites | Maximum
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants (up to)		$ 2,500,000,000