Leases - Lease Cost and Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 22	$ 21	$ 43	$ 42
Operating lease cash flows	8	8	16	16
CECONY | Subsidiaries
Lessee, Lease, Description [Line Items]
Operating lease cost	16	16	33	32
Operating lease cash flows	$ 4	$ 4	$ 9	$ 8