Other Postretirement Benefits - Schedule of Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	$ 397
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	465	$ 397
CECONY
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	371
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	439	371
Other Postretirement Benefits
CHANGE IN BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	1,357	1,114	$ 1,219
Service cost	21	18	20
Interest cost on accumulated other postretirement benefit obligation	37	44	42
Amendments	0	(14)	0
Net actuarial loss/(gain)	74	264	(70)
Benefits paid and administrative expenses, net of subsidies	(117)	(110)	(135)
Participant contributions	53	41	38
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	1,425	1,357	1,114
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	1,026	885	1,039
Actual return on plan assets	142	198	(66)
Employer contributions	7	7	6
Employer group waiver plan subsidies	20	23	34
Participant contributions	53	40	37
Benefits paid	(133)	(127)	(165)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	1,115	1,026	885
FUNDED STATUS	(310)	(331)	(229)
Unrecognized net loss/(gain)	115	155	14
Unrecognized prior service costs	(16)	(19)	(8)
Other Postretirement Benefits | CECONY
CHANGE IN BENEFIT OBLIGATION
Projected benefit obligation at beginning of year	1,154	913	985
Service cost	16	13	14
Interest cost on accumulated other postretirement benefit obligation	31	36	34
Amendments	0	0	0
Net actuarial loss/(gain)	63	252	(32)
Benefits paid and administrative expenses, net of subsidies	(107)	(100)	(125)
Participant contributions	52	40	37
PROJECTED BENEFIT OBLIGATION AT END OF YEAR	1,209	1,154	913
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	872	759	893
Actual return on plan assets	117	165	(54)
Employer contributions	4	6	6
Employer group waiver plan subsidies	19	22	32
Participant contributions	51	40	37
Benefits paid	(123)	(120)	(155)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	940	872	759
FUNDED STATUS	(269)	(282)	(154)
Unrecognized net loss/(gain)	114	149	(2)
Unrecognized prior service costs	$ (1)	$ (3)	$ (5)