Leases Lessee - Supplemental Cash Flow Information Related to Leases (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	$ 225
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	70
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	156
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	11
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	32
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	29
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	20
Potomac Electric Power Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	7
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	7
Delmarva Power and Light Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	6
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	9
Atlantic City Electric 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	$ 4