Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets	[1]	$ 127,767	$ 124,977
Total liabilities	[1]	92,664	90,404
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	[2]	47,372	48,995
Total liabilities	[2]	32,448	$ 33,165
Exelon Generation Co L L C [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Ownership Percentage			50.01%
Exelon Generation Co L L C [Member] | Distributed Energy Company
Variable Interest Entity [Line Items]
Equity Method Investment, Ownership Percentage			31.00%
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		1,145	$ 1,079
Total liabilities		441	260
Exelon's ownership interest in VIE		163	191
Other ownership interests in VIE		541	629
Variable Interest Entity, Not Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets		1,145	1,079
Total liabilities		441	260
Exelon's ownership interest in VIE		163	191
Other ownership interests in VIE		541	629
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		10,386	9,825
Total liabilities		3,539	3,476
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets		10,366	9,805
Total liabilities		3,507	3,432
Commercial Agreement VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		736	636
Total liabilities		216	33
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		520	604
Commercial Agreement VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets		736	636
Total liabilities		216	33
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		520	604
Equity Investment VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		409	443
Total liabilities		225	227
Exelon's ownership interest in VIE		163	191
Other ownership interests in VIE		21	25
Equity Investment VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets		409	443
Total liabilities		225	227
Exelon's ownership interest in VIE		163	191
Other ownership interests in VIE		$ 21	$ 25

[1] Exelon’s consolidated assets include $10,102 million and $9,532 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,531 million and $3,473 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 16 — Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $10,082 million and $9,512 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,499 million and $3,429 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 16 — Variable Interest Entities for additional information.