Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	$ 6	$ 7
Interest cost on accumulated other postretirement benefit obligation	14	18
Expected return on plan assets	(19)	(21)
Recognition of net actuarial loss	16	25
Recognition of prior service cost	(7)	(5)
NET PERIODIC POSTRETIREMENT BENEFIT COST	10	24
Cost capitalized	(3)	(8)
Reconciliation to rate level	12	7
Cost charged to operating expenses	19	23
CECONY [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	5	5
Interest cost on accumulated other postretirement benefit obligation	12	16
Expected return on plan assets	(17)	(18)
Recognition of net actuarial loss	14	22
Recognition of prior service cost	(6)	(4)
NET PERIODIC POSTRETIREMENT BENEFIT COST	8	21
Cost capitalized	(2)	(7)
Reconciliation to rate level	11	4
Cost charged to operating expenses	$ 17	$ 18