Quarterly Data (Details) (USD $) In Millions, except Per Share data	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	663	662	663	661
Earnings Per Share, Basic	$ 0.91	$ 1.28	$ 2.85	$ 3.08
Earnings Per Share Diluted
Average common shares outstanding - diluted	665	663	664	662
Earnings Per Share, Diluted	$ 0.90	$ 1.27	$ 2.84	$ 3.08
Selected Quarterly Financial Information [Line Items]
Revenues	$ 5,295	$ 5,291	$ 14,933	$ 14,150
Operating Income (Loss)	1,181	1,366	3,417	3,786
Net Income Loss	601	845	1,889	2,039
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	2,862	2,655	8,147	7,428
Operating Income (Loss)	754	883	2,203	2,386
Net Income Loss	386	605	1,325	1,548
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,784	1,918	4,694	4,832
Operating Income (Loss)	243	279	697	827
Net Income Loss	112	121	295	246
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	946	1,495	2,942	4,220
Operating Income (Loss)	153	215	524	591
Net Income Loss	$ 105	$ 127	$ 314	$ 303

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