Environmental Matters - Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 5	$ 14	$ 14	$ 24
Insurance recoveries received			5
CECONY [Member]
Environmental Exit Cost [Line Items]
Remediation costs incurred	2	13	10	20
Insurance recoveries received			$ 5