Other Postretirement Benefits - Schedule of Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	$ 326
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	397	$ 326
CECONY
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	301
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	371	301
Other Postretirement Benefits
CHANGE IN BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	1,114	1,219	$ 1,198
Service cost	18	20	20
Interest cost on accumulated other postretirement benefit obligation	44	42	46
Amendments	(14)	0	0
Net actuarial loss/(gain)	264	(70)	53
Benefits paid and administrative expenses, net of subsidies	(110)	(135)	(134)
Participant contributions	41	38	36
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	1,357	1,114	1,219
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	885	1,039	975
Actual return on plan assets	198	(66)	150
Employer contributions	7	6	17
Employer group waiver plan subsidies	23	34	34
Participant contributions	40	37	35
Benefits paid	(127)	(165)	(172)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	1,026	885	1,039
FUNDED STATUS	(331)	(229)	(180)
Unrecognized net loss/(gain)	155	14	(47)
Unrecognized prior service costs	(19)	(8)	(14)
Other Postretirement Benefits | CECONY
CHANGE IN BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	913	985	1,007
Service cost	13	14	13
Interest cost on accumulated other postretirement benefit obligation	36	34	38
Amendments	0	0	0
Net actuarial loss/(gain)	252	(32)	16
Benefits paid and administrative expenses, net of subsidies	(100)	(125)	(124)
Participant contributions	40	37	35
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	1,154	913	985
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	759	893	851
Actual return on plan assets	165	(54)	130
Employer contributions	6	6	8
Employer group waiver plan subsidies	22	32	30
Participant contributions	40	37	35
Benefits paid	(120)	(155)	(161)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	872	759	893
FUNDED STATUS	(282)	(154)	(92)
Unrecognized net loss/(gain)	149	(2)	(85)
Unrecognized prior service costs	$ (3)	$ (5)	$ (7)