Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	$ 26	$ 26	$ 24
Interest cost on accumulated other postretirement benefit obligation	73	83	91
Expected return on plan assets	(85)	(88)	(86)
Recognition of net actuarial loss	98	88	92
Recognition of prior service cost	(21)	(10)	(12)
Recognition of transition obligation	2	4	3
NET PERIODIC BENEFIT COST	93	103	112
Cost capitalized	(32)	(35)	(39)
Reconciliation to rate level	20	14	4
Cost charged to operating expenses	81	82	77
CECONY [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	21	20	19
Interest cost on accumulated other postretirement benefit obligation	63	72	80
Expected return on plan assets	(75)	(78)	(78)
Recognition of net actuarial loss	87	80	85
Recognition of prior service cost	(18)	(11)	(14)
Recognition of transition obligation	2	4	3
NET PERIODIC BENEFIT COST	80	87	95
Cost capitalized	(28)	(29)	(33)
Reconciliation to rate level	16	13	1
Cost charged to operating expenses	$ 68	$ 71	$ 63