Environmental Matters - Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 41	$ 31
Insurance recoveries received		4
CECONY [Member]
Environmental Exit Cost [Line Items]
Remediation costs incurred	35	26
Insurance recoveries received		$ 4