Leases Supplemental Cash Flow Information Related to Leases (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	$ 142
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	30
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	101
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	7
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	2
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	6
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	0
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	16
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	1
Pepco Holdings LLC [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	19
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	15
Potomac Electric Power Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	5
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	6
Delmarva Power and Light Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	4
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	6
Atlantic City Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	3
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 3