Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets	[1]	$ 129,317	$ 124,977
Total liabilities	[1]	94,449	90,404
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	[2]	48,094	48,995
Total liabilities	[2]	33,418	33,165
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		1,178	1,079
Total liabilities		284	260
Exelon's ownership interest in VIE		157	191
Other ownership interests in VIE		737	629
Variable Interest Entity, Not Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets		1,178	1,079
Total liabilities		284	260
Exelon's ownership interest in VIE		157	191
Other ownership interests in VIE		737	629
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		10,481	9,825
Total liabilities		3,606	3,476
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets		10,463	9,805
Total liabilities		3,580	3,432
Commercial Agreement VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		777	636
Total liabilities		61	33
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		716	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		777	636
Total liabilities		61	33
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		716	604
Equity Investment VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		401	443
Total liabilities		223	227
Exelon's ownership interest in VIE		157	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		401	443
Total liabilities		223	227
Exelon's ownership interest in VIE		157	191
Other ownership interests in VIE		$ 21	$ 25

[1] Exelon’s consolidated assets include $10,200 million and $9,532 million at December 31, 2020 and 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,598 million and $3,473 million at December 31, 2020 and 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 23–Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $10,182 million and $9,512 million at December 31, 2020 and 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,572 million and $3,429 million at December 31, 2020 and 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 23–Variable Interest Entities for additional information.