Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Sep. 30, 2019 USD ($)
Derivative [Line Items]
Cash Collateral Posted	$ 18
Financial institutions	1
Investor-owned utilities, marketers and power producers	875
Energy Cooperatives And Municipalities	255
Other	35
Letters Of Credit Posted	55
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	693
Non-investment grade	74
No external ratings - internally rated - investment grade	297
No external ratings - internally rated - non-investment grade	175
Total	1,239
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	10
Non-investment grade	38
No external ratings - internally rated - investment grade	1
No external ratings - internally rated - non-investment grade	24
Total	73
Net Exposure [Member]
Derivative [Line Items]
Investment grade	683
Non-investment grade	36
No external ratings - internally rated - investment grade	296
No external ratings - internally rated - non-investment grade	151
Total	1,166
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	0
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total	0
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	0
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total	$ 0