Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Dec. 31, 2020 USD ($)
Derivative [Line Items]
Cash collateral held	$ 31
Letters of credit held	25
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	577
Non-investment grade	32
Internally rated — investment grade	165
Internally rated — non-investment grade	80
Total	854
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	27
Non-investment grade	0
Internally rated — investment grade	1
Internally rated — non-investment grade	28
Total	56
Net Exposure [Member]
Derivative [Line Items]
Investment grade	550
Non-investment grade	32
Internally rated — investment grade	164
Internally rated — non-investment grade	52
Total	798
Financial institutions	15
Investor-owned utilities, marketers, power producers	607
Energy cooperatives and municipalities	138
Other	38
Total	798
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