Leases - Lease Cost and Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 21	$ 41
Operating lease cash flows	9	17
CECONY
Lessee, Lease, Description [Line Items]
Operating lease cost	16	32
Operating lease cash flows	$ 4	$ 8