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