Intangible Assets Renewable and Alternative Energy Credits (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 1,267	$ 1,228
Finite-Lived Intangible Assets, Accumulated Amortization		1,149	1,255
Finite-Lived Intangible Assets, Net		118	(27)
Exelon Generation Co L L C [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Exelon Generation Co L L C [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		270	312
Exelon Generation Co L L C [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		52	27
Exelon Consolidations [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		2	1
Exelon Consolidations [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		279	321
Exelon Consolidations [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		52	27
PECO Energy Co [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		2	1
PECO Energy Co [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
PECO Energy Co [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Pepco Holdings LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross				$ 25
Pepco Holdings LLC [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Pepco Holdings LLC [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		9	9
Pepco Holdings LLC [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Exelon Enterprise [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	95	95
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	34	25
Finite-Lived Intangible Assets, Net	[1]	61	70
Delmarva Power & Light Company [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Delmarva Power & Light Company [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		8	8
Delmarva Power & Light Company [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Atlantic City Electric Company [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Atlantic City Electric Company [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		1	1
Atlantic City Electric Company [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		$ 0	$ 0

[1] (a)On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term.