Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Cash Collateral Posted	$ 25
Letters Of Credit Posted	9
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash Collateral Posted	781	$ 418
Financial institutions	3
Investor-owned utilities, marketers and power producers	810
Energy Cooperatives And Municipalities	302
Other	60
Letters Of Credit Posted	228	$ 367
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	859
Non-investment grade	30
No external ratings - internally rated - investment grade	204
No external ratings - internally rated - non-investment grade	117
Total	1,210
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade	12
Non-investment grade	11
No external ratings - internally rated - investment grade	1
No external ratings - internally rated - non-investment grade	11
Total	35
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade	847
Non-investment grade	19
No external ratings - internally rated - investment grade	203
No external ratings - internally rated - non-investment grade	106
Total	1,175
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	2
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total	2
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	249
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total	$ 249