Quarterly Data (Details) (USD $)	3 Months Ended									12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Mar. 31, 2012
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	664,000,000		663,000,000	663,000,000	662,000,000	662,000,000	662,000,000	661,000,000	661,000,000	663,000,000		661,000,000		659,000,000
Earnings Per Share, Basic	$ 0.91		$ 0.91	$ 0.93	$ 1.01	$ 0.79	$ 1.28	$ 0.67	$ 1.13
Earnings Per Share Diluted
Average common shares outstanding - diluted	666,000,000		665,000,000	664,000,000	664,000,000	663,000,000	663,000,000	662,000,000	662,000,000	665,000,000		663,000,000		662,000,000
Earnings Per Share, Diluted	$ 0.91		$ 0.90	$ 0.93	$ 1.01	$ 0.79	$ 1.27	$ 0.67	$ 1.13	$ 3.75		$ 3.87		$ 4.09
Selected Quarterly Financial Information [Line Items]
Revenues	$ 3,991,000,000		$ 5,295,000,000	$ 4,587,000,000	$ 5,052,000,000	$ 4,494,000,000	$ 5,291,000,000	$ 4,398,000,000	$ 4,461,000,000	$ 18,924,000,000	[1]	$ 18,644,000,000	[1]	$ 17,318,000,000	[1]
Operating Income (Loss)	1,062,000,000		1,181,000,000	1,034,000,000	1,202,000,000	939,000,000	1,367,000,000	1,018,000,000	1,402,000,000	4,480,000,000		4,726,000,000		4,750,000,000
Net Income Loss	606,000,000		601,000,000	620,000,000	668,000,000	524,000,000	845,000,000	445,000,000	749,000,000	2,495,000,000		2,563,000,000		2,707,000,000
Share Price And Dividend [Abstract]
High Price	45.45		45.27	42.89	43.58	44.49	43.32	45.10	49.88	45.45		44.49
Low Price	39.93		39.51	39.53	39.06	39.05	37.63	37.24	42.97	39.93		39.05
Close	43.37		42.61	42.84	41.24	41.64	42.58	37.97	43.81	43.37		41.64
Dividends	$ 0.525	[2]	$ 0.525	$ 0.525	$ 0.525	$ 0.525	$ 0.525	$ 0.525	$ 0.525	$ 0.525	[2]	$ 0.525				$ 0.525
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	2,161,000,000		2,862,000,000	2,546,000,000	2,739,000,000	2,596,000,000	2,655,000,000	2,353,000,000	2,421,000,000	10,308,000,000	[1]	10,025,000,000	[1]	9,703,000,000	[1]
Operating Income (Loss)	673,000,000		754,000,000	647,000,000	801,000,000	660,000,000	883,000,000	587,000,000	916,000,000	2,876,000,000		3,046,000,000		3,295,000,000
Net Income Loss	446,000,000		386,000,000	443,000,000	495,000,000	424,000,000	605,000,000	382,000,000	561,000,000	1,771,000,000		1,972,000,000		2,122,000,000
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,362,000,000		1,784,000,000	1,444,000,000	1,466,000,000	1,372,000,000	1,918,000,000	1,499,000,000	1,415,000,000	6,056,000,000	[1]	6,204,000,000	[1]	5,774,000,000	[1]
Operating Income (Loss)	285,000,000		243,000,000	254,000,000	200,000,000	229,000,000	280,000,000	256,000,000	291,000,000	982,000,000		1,056,000,000		843,000,000
Net Income Loss	121,000,000		112,000,000	114,000,000	69,000,000	91,000,000	121,000,000	9,000,000	116,000,000	416,000,000		337,000,000		374,000,000
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	778,000,000		946,000,000	842,000,000	1,153,000,000	1,299,000,000	1,469,000,000	1,269,000,000	1,455,000,000	3,720,000,000	[1]	5,519,000,000	[1]	5,311,000,000	[1]
Operating Income (Loss)	131,000,000		153,000,000	161,000,000	210,000,000	70,000,000	215,000,000	182,000,000	194,000,000	655,000,000		661,000,000		697,000,000
Net Income Loss	$ 73,000,000		$ 104,000,000	$ 82,000,000	$ 125,000,000	$ 20,000,000	$ 126,000,000	$ 74,000,000	$ 100,000,000	$ 389,000,000		$ 324,000,000		$ 353,000,000

[1] Includes operating revenues from affiliates.

[2] The fourth quarter 2011 dividend does not include the first quarter 2012 regular quarterly dividend of $0.525 per share, declared by the Exelon Board of Directors on October 25, 2011. The first quarter 2012 dividend is payable on March 9, 2012, to shareholders of record of Exelon at the end of the day on February 15, 2012.