Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total assets	$ 1,079	$ 1,069
Total liabilities	260	259
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	629	587
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	223
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	636	597
Total liabilities	33	37
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	604	560
Commercial Agreement Variable Interest Entities [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	0
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	443	472
Total liabilities	227	222
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	25	27
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	223
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	1,079	1,069
Total liabilities	260	259
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	629	587
Exelon Generation Co L L C [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	223
Exelon Generation Co L L C [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	636	597
Total liabilities	33	37
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	604	560
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	443	472
Total liabilities	227	222
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	25	27
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	$ 223