Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	$ 6	$ 6	$ 12	$ 13
Interest cost on accumulated other postretirement benefit obligation	13	18	27	36
Expected return on plan assets	(19)	(21)	(39)	(42)
Recognition of net actuarial loss	16	24	32	49
Recognition of prior service cost	(7)	(5)	(13)	(11)
Recognition of transition obligation		1		1
NET PERIODIC BENEFIT COST	9	23	19	46
Cost capitalized	(4)	(8)	(7)	(16)
Reconciliation to rate level	16	5	29	14
Cost charged to operating expenses	21	20	41	44
CECONY [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	5	5	9	10
Interest cost on accumulated other postretirement benefit obligation	12	15	23	32
Expected return on plan assets	(17)	(18)	(34)	(38)
Recognition of net actuarial loss	14	21	28	44
Recognition of prior service cost	(6)	(4)	(11)	(9)
Recognition of transition obligation		1		1
NET PERIODIC BENEFIT COST	8	20	15	40
Cost capitalized	(4)	(7)	(6)	(14)
Reconciliation to rate level	13	4	25	8
Cost charged to operating expenses	$ 17	$ 17	$ 34	$ 34