Intangible Assets - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross	$ 1,253	$ 1,295
Accumulated Amortization	(1,081)	(1,121)
Net	172	174
Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	1,963	1,967
Accumulated Amortization	(1,642)	(1,612)
Net	321	355
Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	326	343
Accumulated Amortization	(215)	(190)
Net	111	153
Exelon Generation Co L L C [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	222	243
Accumulated Amortization	(197)	(193)
Net	25	50
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	162	162
Accumulated Amortization	(162)	(155)
Net	0	7
Pepco Holdings LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	(1,515)	(1,515)
Accumulated Amortization	1,188	1,073
Net	(327)	(442)
Business Services Company [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	95	95
Accumulated Amortization	(53)	(44)
Net	$ 42	$ 51