Intangible Assets - Schedule of Goodwill (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,625
Goodwill from business combination	47
Goodwill, ending balance	2,672
Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	2,625
Goodwill from business combination	0
Goodwill, ending balance	2,625
Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance			0
Goodwill, ending balance	47		0
Goodwill Gross [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	4,608
Goodwill from business combination	47
Goodwill, ending balance	4,655
Goodwill Gross [Member] | Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	4,608	[1]
Goodwill from business combination	0
Goodwill, ending balance	4,608	[1]
Goodwill Gross [Member] | Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	0
Goodwill from business combination	47
Goodwill, ending balance	47
Goodwill Accumulated Impairment Losses [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	1,983
Goodwill from business combination	0
Goodwill, ending balance	1,983
Goodwill Accumulated Impairment Losses [Member] | Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	1,983
Goodwill from business combination	0
Goodwill, ending balance	1,983
Goodwill Accumulated Impairment Losses [Member] | Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	0
Goodwill from business combination	47
Goodwill, ending balance	$ 47

[1] Reflects goodwill recorded in 2000 from the PECO/Unicom (predecessor parent company of ComEd) merger net of amortization, resolution of tax matters and other non-impairment-related changes as allowed under previous authoritative guidance.