Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income by Component (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated OCI, net of taxes	$ (50)	$ (53)		$ (53)
OCI before reclassifications		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
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	2	3	(1)	5	6
Accumulated OCI, net of taxes	(48)	(50)		(48)
CECONY [Member]
Accumulated OCI, net of taxes	(9)	(9)		(9)
OCI before reclassifications
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)		(2)
Accumulated OCI, net of taxes	$ (9)	$ (9)		$ (9)