Lessee - Schedule of Rent Expense Under Prior Lease Guidance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Operating Leases, Rent Expense	$ 670
Operating Lease, Liability		$ 1,302	$ 1,532
Exelon Generation Co L L C [Member]
Operating Leases, Rent Expense	558
Operating Lease, Liability		907	1,082
Commonwealth Edison Co [Member]
Operating Leases, Rent Expense	7
Operating Lease, Liability		8	11
PECO Energy Co [Member]
Operating Leases, Rent Expense	10
Operating Lease, Liability		1	1
Baltimore Gas and Electric Company [Member]
Operating Leases, Rent Expense	35
Operating Lease, Liability		64	82
Pepco Holdings LLC [Member]
Operating Leases, Rent Expense	48
Operating Lease, Liability		255	285
Potomac Electric Power Company [Member]
Operating Leases, Rent Expense	10
Operating Lease, Liability		52	57
Delmarva Power & Light Company [Member]
Operating Leases, Rent Expense	13
Operating Lease, Liability		65	74
Atlantic City Electric Company [Member]
Operating Leases, Rent Expense	8
Operating Lease, Liability		15	18
Long-term Contract for Purchase of Electric Power [Member]
Operating Lease, Liability		528	664
Long-term Contract for Purchase of Electric Power [Member] | Exelon Generation Co L L C [Member]
Operating Lease, Liability	$ 493	$ 528	$ 664