Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets	$ 1,126	$ 1,079
Total liabilities	381	260
Exelon's ownership interest in VIE	183	191
Other ownership interests in VIE	563	629
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	695	636
Total liabilities	158	33
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	538	604
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	431	443
Total liabilities	223	227
Exelon's ownership interest in VIE	183	191
Other ownership interests in VIE	25	25
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	1,126	1,079
Total liabilities	381	260
Exelon's ownership interest in VIE	183	191
Other ownership interests in VIE	563	629
Exelon Generation Co L L C [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	0	0
Exelon Generation Co L L C [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	695	636
Total liabilities	158	33
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	538	604
Exelon Generation Co L L C [Member] | Commercial Agreement Variable Interest Entities [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	0	0
Exelon Generation Co L L C [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	431	443
Total liabilities	223	227
Exelon's ownership interest in VIE	183	191
Other ownership interests in VIE	25	25
Exelon Generation Co L L C [Member] | Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	$ 0	$ 0