Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4	$ 16	$ 13
Interest cost on accumulated other postretirement benefit obligation	9	11	28	33
Expected return on plan assets	(16)	(16)	(49)	(49)
Recognition of net actuarial loss/(gain)	3	(2)	34	(6)
Recognition of prior service credit	(1)	(1)	(3)	(2)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	0	(4)	26	(11)
Cost capitalized	(2)	(1)	(7)	(6)
Reconciliation to rate level	2	3	(19)	10
Total credit recognized	0	(2)	0	(7)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3	12	9
Interest cost on accumulated other postretirement benefit obligation	8	9	23	27
Expected return on plan assets	(14)	(14)	(41)	(41)
Recognition of net actuarial loss/(gain)	3	(2)	32	(7)
Recognition of prior service credit	0	0	(1)	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	1	(4)	25	(13)
Cost capitalized	(2)	(2)	(5)	(4)
Reconciliation to rate level	0	2	(24)	6
Total credit recognized	$ (1)	$ (4)	$ (4)	$ (11)