Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Total assets	[1]	$ 132,621	$ 129,317
Total liabilities	[1]	98,362	94,449
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		1,151	1,178
Total liabilities		289	284
Exelon's ownership interest in VIE		143	157
Other ownership interests in VIE		719	737
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	[2]	48,010	48,094
Total liabilities	[2]	35,975	33,418
Exelon Generation Co L L C [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		1,151	1,178
Total liabilities		289	284
Exelon's ownership interest in VIE		143	157
Other ownership interests in VIE		719	737
Commercial Agreement VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		781	777
Total liabilities		80	61
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		701	716
Commercial Agreement VIE [Member] | Exelon Generation Co L L C [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		781	777
Total liabilities		80	61
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		701	716
Equity Investment VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		370	401
Total liabilities		209	223
Exelon's ownership interest in VIE		143	157
Other ownership interests in VIE		18	21
Equity Investment VIE [Member] | Exelon Generation Co L L C [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		370	401
Total liabilities		209	223
Exelon's ownership interest in VIE		143	157
Other ownership interests in VIE		$ 18	$ 21

[1] Exelon’s consolidated assets include $2,722 million and $10,200 million at September 30, 2021 and December 31, 2020, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $1,088 million and $3,598 million at September 30, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 17 — Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $2,704 million and $10,182 million at September 30, 2021 and December 31, 2020, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $1,078 million and $3,572 million at September 30, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 17 — Variable Interest Entities for additional information.