Pension Benefits - Schedule of Funded Status (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CHANGE IN PROJECTED BENEFIT OBLIGATION
Benefit obligation at beginning of year	$ 13,406	$ 11,825	$ 10,307
Service cost - excluding administrative expenses	259	224	186
Interest cost on projected benefit obligation	537	547	560
Net actuarial (gain)/loss	(1,469)	1,323	1,251
Benefits paid	(536)	(513)	(479)
BENEFIT OBLIGATION AT END OF YEAR	12,197	13,406	11,825
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	9,135	7,800	7,721
Actual return on plan assets	1,310	1,094	37
Employer contributions	879	785	542
Benefits paid	(536)	(513)	(479)
Administrative expenses	(33)	(31)	(21)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	10,755	9,135	7,800
FUNDED STATUS	(1,442)	(4,271)	(4,025)
Unrecognized net loss	2,759	5,594	5,351
Unrecognized prior service costs	17	23	30
Accumulated benefit obligation	11,004	11,911	10,595
CECONY [Member]
CHANGE IN PROJECTED BENEFIT OBLIGATION
Benefit obligation at beginning of year	12,572	11,072	9,653
Service cost - excluding administrative expenses	241	209	174
Interest cost on projected benefit obligation	503	513	524
Net actuarial (gain)/loss	(1,388)	1,255	1,166
Benefits paid	(499)	(477)	(445)
BENEFIT OBLIGATION AT END OF YEAR	11,429	12,572	11,072
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	8,668	7,406	7,340
Actual return on plan assets	1,241	1,040	33
Employer contributions	819	729	498
Benefits paid	(499)	(477)	(445)
Administrative expenses	(32)	(30)	(20)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	10,197	8,668	7,406
FUNDED STATUS	(1,232)	(3,904)	(3,666)
Unrecognized net loss	2,617	5,297	5,063
Unrecognized prior service costs	6	10	16
Accumulated benefit obligation	$ 10,268	$ 11,116	$ 9,876