Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Mar. 31, 2021 USD ($)
Derivative [Line Items]
Cash Collateral Held	$ 32
Letters Of Credit Held	29
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	431
Non-investment grade	43
Internally rated - investment grade	146
Internally rated - non-investment grade	70
Total	690
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	31
Non-investment grade	4
Internally rated - investment grade	1
Internally rated - non-investment grade	25
Total	61
Net Exposure [Member]
Derivative [Line Items]
Investment grade	400
Non-investment grade	39
Internally rated - investment grade	145
Internally rated - non-investment grade	45
Total	629
Investor-owned utilities, marketers and power producers	451
Energy Cooperatives And Municipalities	123
Other	55
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	0
Total	0
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	0
Total	$ 0