Quarterly Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	855	705
Earnings Per Share, Basic	$ (0.01)	$ 0.28
Earnings Per Share Diluted
Average common shares outstanding - diluted	855	707
Earnings Per Share, Diluted	$ (0.01)	$ 0.28
Selected Quarterly Financial Information [Line Items]
Revenues	$ 6,082	$ 4,690
Operating Income (Loss)	508	359
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	1	200
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	3,533	2,743
Operating Income (Loss)	(64)	272
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(17)	166
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,160	1,388
Operating Income (Loss)	209	226
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(81)	87
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	895	875
Operating Income (Loss)	203	177
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	122	97
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	880	697
Operating Income (Loss)	163	(11)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 80	$ (30)