Environmental Matters - Environmental Remediation Costs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 9	$ 8	$ 12	$ 15
CECONY
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 3	$ 7	$ 5	$ 12