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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, accumulated OCI, net of taxes	$ (21)	$ (50)	$ (25)	$ (53)
OCI before reclassifications, net of tax	0	0	2	1
Amounts reclassified from accumulated OCI related to pension and other postretirement benefit plan liabilities, net of tax	1	2	3	4
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	2	5	5
Ending balance, accumulated OCI, net of taxes	(20)	(48)	(20)	(48)
CECONY [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, accumulated OCI, net of taxes	(5)	(9)	(6)	(9)
OCI before reclassifications, net of tax	0	0	0	0
Amounts reclassified from accumulated OCI related to pension and other postretirement benefit plan liabilities, net of tax	0	0	1	0
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	0	0	1	0
Ending balance, accumulated OCI, net of taxes	$ (5)	$ (9)	$ (5)	$ (9)