Environmental Matters - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Site Contingency [Line Items]
Remediation cost estimate	$ 37	$ 29
Other Superfund Sites
Site Contingency [Line Items]
Remediation cost estimate	51
Other Superfund Sites | Manufactured gas plant sites | Maximum
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants (up to)	2,800
CECONY
Site Contingency [Line Items]
Remediation cost estimate	$ 34	$ 20
CECONY | Asbestos Proceedings
Site Contingency [Line Items]
Estimated undiscounted asbestos liability (years)	15 years
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Remediation cost estimate	$ 36
CECONY | Other Superfund Sites | Manufactured gas plant sites | Maximum
Site Contingency [Line Items]
Estimated aggregate undiscounted potential liability related environmental contaminants (up to)	$ 2,700