Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 5	$ 9	$ 10
Interest cost on accumulated other postretirement benefit obligation	11	11	22	21
Expected return on plan assets	(16)	(18)	(33)	(37)
Recognition of net actuarial loss/(gain)	(2)	2	(4)	4
Recognition of prior service cost/(credit)	(1)	(2)	(2)	(3)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	(4)	(2)	(8)	(5)
Cost capitalized	(2)	(2)	(4)	(4)
Reconciliation to rate level	3	2	7	5
Total expense/(credit) recognized	(3)	(2)	(5)	(4)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	6	7
Interest cost on accumulated other postretirement benefit obligation	9	9	18	17
Expected return on plan assets	(14)	(16)	(27)	(31)
Recognition of net actuarial loss/(gain)	(2)	1	(5)	1
Recognition of prior service cost/(credit)	0	(1)	(1)	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	(4)	(4)	(9)	(7)
Cost capitalized	(2)	(1)	(3)	(3)
Reconciliation to rate level	2	2	4	5
Total expense/(credit) recognized	$ (4)	$ (3)	$ (8)	$ (5)