Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 237	$ 190	$ 168
Interest cost on projected benefit obligation	547	560	556
Expected return on plan assets	(705)	(734)	(704)
Recognition of net actuarial loss	709	530	425
Recognition of prior service costs	8	8	8
NET PERIODIC BENEFIT COST	796	554	453
Amortization of regulatory asset	2	2	2
TOTAL PERIODIC BENEFIT COST	798	556	455
Cost capitalized	(277)	(185)	(157)
Reconciliation to rate level	(8)	(65)	(115)
Cost charged to operating expenses	513	306	183
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	220	177	157
Interest cost on projected benefit obligation	513	524	521
Expected return on plan assets	(670)	(698)	(670)
Recognition of net actuarial loss	670	501	401
Recognition of prior service costs	6	6	6
NET PERIODIC BENEFIT COST	739	510	415
Amortization of regulatory asset	2	2	2
TOTAL PERIODIC BENEFIT COST	741	512	417
Cost capitalized	(260)	(172)	(146)
Reconciliation to rate level	(12)	(68)	(113)
Cost charged to operating expenses	$ 469	$ 272	$ 158