Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, Gross	$ 8,660	$ 8,660	$ 8,660
Goodwill, beginning balance	6,677	6,677
Impairment losses	0	0
Goodwill, ending balance	6,677	6,677
Goodwill, Impaired, Accumulated Impairment Loss	1,983	1,983	1,983
Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	47
Goodwill, ending balance	47	47
Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, Gross	4,608	4,608	4,608
Goodwill, beginning balance	2,625	2,625
Impairment losses	0	0
Goodwill, ending balance	2,625	2,625
Goodwill, Impaired, Accumulated Impairment Loss	1,983	1,983	1,983
Delmarva Power & Light Company [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	8
Goodwill, ending balance	8	8
Pepco Holdings LLC [Member]
Goodwill [Roll Forward]
Goodwill, Gross	4,005	4,005	$ 4,005
Goodwill, beginning balance	4,005	4,005
Impairment losses	0
Goodwill, ending balance	$ 4,005	$ 4,005