Pension Benefits - Schedule of Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	$ 273
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	330	$ 273
Pension Benefits
CHANGE IN PROJECTED BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	14,095	14,377	$ 15,081
Service cost – excluding administrative expenses	259	271	293
Interest cost on projected benefit obligation	591	596	575
Net actuarial loss/(gain)	1,231	(302)	(996)
Plan amendments	6	(256)	0
Benefits paid	(646)	(591)	(576)
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	15,536	14,095	14,377
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	12,472	11,759	11,495
Actual return on plan assets	2,041	829	126
Employer contributions	450	508	750
Benefits paid	(646)	(591)	(576)
Administrative expenses	(43)	(33)	(36)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	14,274	12,472	11,759
FUNDED STATUS	(1,262)	(1,623)	(2,618)
Unrecognized net loss	2,760	3,157	3,909
Unrecognized prior service costs	(223)	(244)	16
Accumulated benefit obligation	13,897	12,655	12,909
CECONY
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	246
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	301	246
CECONY | Pension Benefits
CHANGE IN PROJECTED BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	13,203	13,482	14,137
Service cost – excluding administrative expenses	241	254	274
Interest cost on projected benefit obligation	554	559	538
Net actuarial loss/(gain)	1,171	(282)	(931)
Plan amendments	0	(259)	0
Benefits paid	(602)	(551)	(536)
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	14,567	13,203	13,482
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	11,815	11,141	10,897
Actual return on plan assets	1,935	787	118
Employer contributions	412	469	697
Benefits paid	(602)	(551)	(536)
Administrative expenses	(41)	(31)	(35)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	13,519	11,815	11,141
FUNDED STATUS	(1,048)	(1,388)	(2,341)
Unrecognized net loss	2,624	2,995	3,704
Unrecognized prior service costs	(242)	(258)	3
Accumulated benefit obligation	$ 12,972	$ 11,806	$ 12,055