Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 5	$ 13	$ 15
Interest cost on accumulated other postretirement benefit obligation	11	11	33	32
Expected return on plan assets	(16)	(18)	(49)	(55)
Recognition of net actuarial loss/(gain)	(2)	2	(6)	6
Recognition of prior service cost/(credit)	(1)	(2)	(2)	(5)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	(4)	(2)	(11)	(7)
Cost capitalized	(1)	(2)	(6)	(6)
Reconciliation to rate level	3	2	10	6
Total expense/(credit) recognized	(2)	(2)	(7)	(7)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	9	10
Interest cost on accumulated other postretirement benefit obligation	9	9	27	26
Expected return on plan assets	(14)	(16)	(41)	(47)
Recognition of net actuarial loss/(gain)	(2)	1	(7)	2
Recognition of prior service cost/(credit)	0	(1)	(1)	(2)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	(4)	(4)	(13)	(11)
Cost capitalized	(2)	(1)	(4)	(4)
Reconciliation to rate level	2	2	6	7
Total expense/(credit) recognized	$ (4)	$ (3)	$ (11)	$ (8)