Quarterly Data (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	705,000,000	662,000,000
Earnings Per Share, Basic	$ 0.28	$ 1.01
Earnings Per Share Diluted
Average common shares outstanding - diluted	707,000,000	664,000,000
Earnings Per Share, Diluted	$ 0.28	$ 1.01
Selected Quarterly Financial Information [Line Items]
Revenues	$ 4,686,000,000	$ 4,956,000,000
Operating Income (Loss)	359,000,000	1,202,000,000
Net Income Loss	200,000,000	669,000,000
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	2,739,000,000	2,643,000,000
Operating Income (Loss)	272,000,000	801,000,000
Net Income Loss	166,000,000	495,000,000
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,388,000,000	1,466,000,000
Operating Income (Loss)	226,000,000	200,000,000
Net Income Loss	87,000,000	69,000,000
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	875,000,000	1,153,000,000
Operating Income (Loss)	177,000,000	210,000,000
Net Income Loss	97,000,000	126,000,000
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	696,000,000	976,000,000
Operating Income (Loss)	(11,000,000)	153,000,000
Net Income Loss	$ (30,000,000)	$ 81,000,000