Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 21	$ 18	$ 20
Interest cost on accumulated other postretirement benefit obligation	37	44	42
Expected return on plan assets	(66)	(66)	(73)
Recognition of net actuarial loss/(gain)	37	(9)	8
Recognition of prior service credit	(3)	(2)	(6)
TOTAL PERIODIC POSTRETIREMENT BENEFIT COST/(CREDIT)	26	(15)	(9)
Cost capitalized	(9)	(7)	(8)
Reconciliation to rate level	(17)	12	8
Total credit recognized	0	(10)	(9)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	16	13	14
Interest cost on accumulated other postretirement benefit obligation	31	36	34
Expected return on plan assets	(54)	(54)	(63)
Recognition of net actuarial loss/(gain)	36	(10)	3
Recognition of prior service credit	(2)	(2)	(2)
TOTAL PERIODIC POSTRETIREMENT BENEFIT COST/(CREDIT)	27	(17)	(14)
Cost capitalized	(7)	(5)	(6)
Reconciliation to rate level	(25)	7	9
Total credit recognized	$ (5)	$ (15)	$ (11)