Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4	$ 11	$ 9
Interest cost on accumulated other postretirement benefit obligation	9	11	19	22
Expected return on plan assets	(16)	(16)	(33)	(33)
Recognition of net actuarial loss/(gain)	3	(2)	30	(4)
Recognition of prior service credit	(1)	(1)	(2)	(2)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	0	(4)	25	(8)
Cost capitalized	(2)	(2)	(5)	(4)
Reconciliation to rate level	2	3	(20)	7
Total credit recognized	0	(3)	0	(5)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3	8	6
Interest cost on accumulated other postretirement benefit obligation	8	9	16	18
Expected return on plan assets	(14)	(14)	(27)	(27)
Recognition of net actuarial loss/(gain)	3	(2)	29	(5)
Recognition of prior service credit	0	0	(1)	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	1	(4)	25	(9)
Cost capitalized	(2)	(2)	(3)	(3)
Reconciliation to rate level	0	2	(24)	4
Total credit recognized	$ (1)	$ (4)	$ (2)	$ (8)