Leases - Lease Cost and Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 21	$ 21	$ 63	$ 62
Operating lease cash flows	10	10	27	27
CECONY
Lessee, Lease, Description [Line Items]
Operating lease cost	16	16	48	48
Operating lease cash flows	$ 6	$ 5	$ 13	$ 13