Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 7	$ 5	$ 13	$ 11
Interest cost on projected other postretirement benefit obligation	8	9	16	19
Expected return on plan assets	(17)	(16)	(34)	(33)
Recognition of net actuarial loss/(gain)	6	3	12	30
Recognition of prior service credit	(1)	(1)	(1)	(2)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	3	0	6	25
Cost capitalized	(3)	(2)	(6)	(5)
Reconciliation to rate level	0	2	0	(20)
Total credit recognized	0	0	0	0
CECONY | Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	5	4	10	8
Interest cost on projected other postretirement benefit obligation	7	8	13	16
Expected return on plan assets	(14)	(14)	(27)	(27)
Recognition of net actuarial loss/(gain)	5	3	10	29
Recognition of prior service credit	0	0	(1)	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	3	1	5	25
Cost capitalized	(3)	(2)	(5)	(3)
Reconciliation to rate level	(1)	0	(3)	(24)
Total credit recognized	$ (1)	$ (1)	$ (3)	$ (2)