Leases - Lease Cost and Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 21	$ 21	$ 42	$ 41
Operating lease cash flows	8	9	16	17
CECONY
Lessee, Lease, Description [Line Items]
Operating lease cost	16	16	32	32
Operating lease cash flows	$ 4	$ 4	$ 8	$ 8