Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) $ in Millions	Mar. 31, 2020 USD ($)
Derivative [Line Items]
Cash Collateral Held	$ 29
Letters Of Credit Held	65
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	915
Non-investment grade	60
Internally rated - investment grade	228
Internally rated - non-investment grade	157
Total	1,360
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade	22
Non-investment grade	49
Internally rated - investment grade	1
Internally rated - non-investment grade	22
Total	94
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade	893
Non-investment grade	11
Internally rated - investment grade	227
Internally rated - non-investment grade	135
Total	1,266
Financial institutions	18
Investor-owned utilities, marketers and power producers	983
Energy Cooperatives And Municipalities	224
Other	41
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	0
Total	0
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	0
Total	$ 0