Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Total assets	[1]	$ 130,000	$ 129,317
Total liabilities	[1]	95,687	94,449
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		1,175	1,178
Total liabilities		313	284
Exelon's ownership interest in VIE		150	157
Other ownership interests in VIE		712	737
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	[2]	47,326	48,094
Total liabilities	[2]	33,886	33,418
Exelon Generation Co L L C [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		1,175	1,178
Total liabilities		313	284
Exelon's ownership interest in VIE		150	157
Other ownership interests in VIE		712	737
Commercial Agreement VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		789	777
Total liabilities		95	61
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		694	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		789	777
Total liabilities		95	61
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		694	716
Equity Investment VIE [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total assets		386	401
Total liabilities		218	223
Exelon's ownership interest in VIE		150	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		386	401
Total liabilities		218	223
Exelon's ownership interest in VIE		150	157
Other ownership interests in VIE		$ 18	$ 21

[1] Exelon’s consolidated assets include $9,985 million and $10,200 million at March 31, 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 $3,578 million and $3,598 million at March 31, 2021 and December 31, 2020, 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 $9,967 million and $10,182 million at March 31, 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 $3,557 million and $3,572 million at March 31, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 16 — Variable Interest Entities for additional information.