Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total assets	$ 1,056	$ 1,069
Total liabilities	258	259
Exelon's ownership interest in VIE	203	223
Other ownership interests in VIE	596	587
Registrants' maximum exposure to loss	16	15
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	203	223
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	7	7
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	603	597
Total liabilities	33	37
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	571	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
Commercial Agreement Variable Interest Entities [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	7	7
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	453	472
Total liabilities	225	222
Exelon's ownership interest in VIE	203	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	203	223
Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	0	0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	1,056	1,069
Total liabilities	258	259
Exelon's ownership interest in VIE	203	223
Other ownership interests in VIE	596	587
Registrants' maximum exposure to loss	12	13
Exelon Generation Co L L C [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	203	223
Exelon Generation Co L L C [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	7	7
Exelon Generation Co L L C [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	603	597
Total liabilities	33	37
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	571	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] | Commercial Agreement Variable Interest Entities [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	7	7
Exelon Generation Co L L C [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	453	472
Total liabilities	225	222
Exelon's ownership interest in VIE	203	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	203	223
Exelon Generation Co L L C [Member] | Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	$ 0	$ 0