Goodwill (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2010
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,625.00
Goodwill Impairment Loss	0
Goodwill, ending balance	2,625.00
Goodwill Gross [Member]
Goodwill [Roll Forward]
Goodwill Impairment Loss	0	[1]
Goodwill, ending balance	4,608.00	[1]
Goodwill Accumulated Impairment Losses [Member]
Goodwill [Roll Forward]
Goodwill Impairment Loss	0
Goodwill, ending balance	1,983.00
Commonwealth Edison Co [Member]
Goodwill, Impaired [Abstract]
Annual revenue requirement reduction	168.00
Goodwill [Roll Forward]
Goodwill, beginning balance	2,625.00		2,625.00
Goodwill Impairment Loss	0
Goodwill, ending balance	2,625.00		2,625.00
Commonwealth Edison Co [Member] | Goodwill Gross [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	4,608.00		4,608.00
Goodwill Impairment Loss	0	[1]
Goodwill, ending balance	4,608.00	[1]	4,608.00
Commonwealth Edison Co [Member] | Goodwill Accumulated Impairment Losses [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	1,983.00		1,983.00
Goodwill Impairment Loss	0
Goodwill, ending balance	$ 1,983.00		$ 1,983.00

[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.