Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income by Component (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated OCI, net of taxes	$ (48)	$ (50)	$ (53)		$ (53)
OCI before reclassifications, net of tax			1
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax of $1 and $- for Con Edison and CECONY, respectively	2	2	2
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	2	2	3	2	7	8
Accumulated OCI, net of taxes	(46)	(48)	(50)		(46)
CECONY [Member]
Accumulated OCI, net of taxes	(9)	(9)	(9)		(9)
OCI before reclassifications, net of tax
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax of $1 and $- for Con Edison and CECONY, respectively
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES						(2)
Accumulated OCI, net of taxes	$ (9)	$ (9)	$ (9)		$ (9)