Lessee - Schedule of Rent Expense Under Prior Lease Guidance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Operating Lease, Liability			$ 1,532
Operating Leases, Rent Expense	$ 670	$ 709
Exelon Generation Co L L C [Member]
Operating Lease, Liability			1,082
Operating Leases, Rent Expense	558	578
Commonwealth Edison Co [Member]
Operating Lease, Liability			11
Operating Leases, Rent Expense	7	9
PECO Energy Co [Member]
Operating Lease, Liability			1
Operating Leases, Rent Expense	10	9
Baltimore Gas and Electric Company [Member]
Operating Lease, Liability			82
Operating Leases, Rent Expense	35	32
Pepco Holdings LLC [Member]
Operating Lease, Liability			285
Operating Leases, Rent Expense	48	63
Potomac Electric Power Company [Member]
Operating Lease, Liability			57
Operating Leases, Rent Expense	10	11
Delmarva Power & Light Company [Member]
Operating Lease, Liability			74
Operating Leases, Rent Expense	13	16
Atlantic City Electric Company [Member]
Operating Lease, Liability			18
Operating Leases, Rent Expense	8	14
Long-term Contract for Purchase of Electric Power [Member]
Operating Lease, Liability			664
Long-term Contract for Purchase of Electric Power [Member] | Exelon Generation Co L L C [Member]
Operating Lease, Liability	$ 493	$ 508	$ 664