Quarterly Data (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	854,000,000	663,000,000	804,000,000	663,000,000
Earnings Per Share, Basic	$ 0.35	$ 0.91	$ 0.97	$ 2.85
Earnings Per Share Diluted
Average common shares outstanding - diluted	857,000,000	665,000,000	806,000,000	664,000,000
Earnings Per Share, Diluted	$ 0.35	$ 0.90	$ 0.97	$ 2.84
Selected Quarterly Financial Information [Line Items]
Revenues	$ 6,565,000,000	$ 5,254,000,000	$ 17,205,000,000	$ 14,705,000,000
Operating Income (Loss)	603,000,000	1,181,000,000	1,676,000,000	3,417,000,000
Net Income Loss	297,000,000	602,000,000	787,000,000	1,892,000,000
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	4,017,000,000	2,821,000,000	10,509,000,000	7,919,000,000
Operating Income (Loss)	174,000,000	754,000,000	830,000,000	2,203,000,000
Net Income Loss	87,000,000	386,000,000	419,000,000	1,325,000,000
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,484,000,000	1,784,000,000	4,154,000,000	4,694,000,000
Operating Income (Loss)	218,000,000	243,000,000	586,000,000	697,000,000
Net Income Loss	90,000,000	112,000,000	219,000,000	295,000,000
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	806,000,000	946,000,000	2,396,000,000	2,942,000,000
Operating Income (Loss)	178,000,000	153,000,000	506,000,000	524,000,000
Net Income Loss	123,000,000	105,000,000	300,000,000	314,000,000
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	720,000,000	745,000,000	2,032,000,000	2,394,000,000
Operating Income (Loss)	30,000,000	23,000,000	71,000,000	229,000,000
Net Income Loss	$ 0	$ 2,000,000	$ (14,000,000)	$ 99,000,000