Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) $ in Millions	Jun. 30, 2020 USD ($)
Derivative [Line Items]
Cash Collateral Held	$ 31
Letters Of Credit Held	38
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	772
Non-investment grade	35
Internally rated - investment grade	213
Internally rated - non-investment grade	130
Total	1,150
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade	25
Non-investment grade	26
Internally rated - investment grade	1
Internally rated - non-investment grade	17
Total	69
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade	747
Non-investment grade	9
Internally rated - investment grade	212
Internally rated - non-investment grade	113
Total	1,081
Financial institutions	29
Investor-owned utilities, marketers and power producers	834
Energy Cooperatives And Municipalities	173
Other	45
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	1
Total	1
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	117
Total	$ 117