Pension Benefits - Funded Status (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]
Benefit obligation at beginning of year	$ 11,825	$ 10,307	$ 9,408
Service cost - excluding administrative expenses	224	186	160
Interest cost on projected benefit obligation	547	560	556
Plan amendments			6
Net actuarial loss	1,323	1,251	636
Benefits paid	(513)	(479)	(459)
BENEFIT OBLIGATION AT END OF YEAR	13,406	11,825	10,307
Beginning Balance as of January 1, 2011	7,800	7,721	6,877
Actual return on plan assets	1,094	37	888
Employer contributions	785	542	443
Benefits paid	(513)	(479)	(459)
Administrative expenses	(31)	(21)	(28)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	9,135	7,800	7,721
FUNDED STATUS	(4,271)	(4,025)	(2,586)
Unrecognized net loss	5,594	5,351	3,915
Unrecognized prior service costs	23	30	38
Accumulated benefit obligation	11,911	10,595	9,319
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	11,072	9,653	8,803
Service cost - excluding administrative expenses	209	174	149
Interest cost on projected benefit obligation	513	524	521
Plan amendments
Net actuarial loss	1,255	1,166	607
Benefits paid	(477)	(445)	(427)
BENEFIT OBLIGATION AT END OF YEAR	12,572	11,072	9,653
Beginning Balance as of January 1, 2011	7,406	7,340	6,544
Actual return on plan assets	1,040	33	846
Employer contributions	729	498	404
Benefits paid	(477)	(445)	(427)
Administrative expenses	(30)	(20)	(27)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	8,668	7,406	7,340
FUNDED STATUS	(3,904)	(3,666)	(2,313)
Unrecognized net loss	5,297	5,063	3,716
Unrecognized prior service costs	10	16	22
Accumulated benefit obligation	$ 11,116	$ 9,876	$ 8,694