Other Postretirement 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
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
Other Postretirement Benefits
CHANGE IN BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	1,198	1,287	$ 1,411
Service cost	20	18	20
Interest cost on accumulated other postretirement benefit obligation	46	48	51
Amendments	0	0	0
Net actuarial loss/(gain)	53	(57)	(103)
Benefits paid and administrative expenses	(134)	(134)	(127)
Participant contributions	36	36	35
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	1,219	1,198	1,287
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	975	994	1,084
Actual return on plan assets	150	60	(6)
Employer contributions	17	7	6
EGWP payments	34	35	28
Participant contributions	35	36	35
Benefits paid	(172)	(157)	(153)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	1,039	975	994
FUNDED STATUS	(180)	(223)	(293)
Unrecognized net loss/(gain)	(47)	(24)	28
Unrecognized prior service costs	(14)	(31)	(51)
Other Postretirement Benefits | CECONY
CHANGE IN BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	1,007	1,093	1,203
Service cost	13	13	15
Interest cost on accumulated other postretirement benefit obligation	38	40	43
Amendments	0	0	0
Net actuarial loss/(gain)	16	(52)	(85)
Benefits paid and administrative expenses	(124)	(122)	(117)
Participant contributions	35	35	34
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	985	1,007	1,093
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	851	870	950
Actual return on plan assets	130	52	(4)
Employer contributions	8	7	6
EGWP payments	30	33	26
Participant contributions	35	35	34
Benefits paid	(161)	(146)	(142)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	893	851	870
FUNDED STATUS	(92)	(156)	(223)
Unrecognized net loss/(gain)	(85)	(42)	4
Unrecognized prior service costs	$ (7)	$ (18)	$ (32)