Quarterly Data (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	854.00	854.00	853.00	705.00	664.00		663.00	663.00	662.00	816.00	663.00		661.00
Earnings Per Share, Basic	$ 0.44	$ 0.35	$ 0.34	$ 0.28	$ 0.91		$ 0.91	$ 0.93	$ 1.01
Earnings Per Share Diluted
Average common shares outstanding - diluted	857.00	857.00	856.00	707.00	666.00		665.00	664.00	664.00	819.00	665.00		663.00
Earnings Per Share, Diluted	$ 0.44	$ 0.35	$ 0.33	$ 0.28	$ 0.91		$ 0.90	$ 0.93	$ 1.01	$ 1.42	$ 3.75		$ 3.87
Selected Quarterly Financial Information [Line Items]
Revenues	$ 6,284,000,000	$ 6,565,000,000	$ 5,954,000,000	$ 4,686,000,000	$ 4,357,000,000		$ 5,254,000,000	$ 4,496,000,000	$ 4,956,000,000	$ 23,489,000,000	$ 19,063,000,000		$ 18,644,000,000
Operating Income (Loss)	704,000,000	603,000,000	714,000,000	359,000,000	1,062,000,000		1,181,000,000	1,034,000,000	1,202,000,000	2,380,000,000	4,479,000,000		4,726,000,000
Net Income Loss	378,000,000	296,000,000	286,000,000	200,000,000	606,000,000		601,000,000	620,000,000	668,000,000	1,171,000,000	2,499,000,000		2,563,000,000
Share Price And Dividend [Abstract]
High Price	37.50	39.82	39.37	43.70	45.45		45.27	42.89	43.58	37.50	45.45
Low Price	28.40	34.54	36.27	38.31	39.93		39.51	39.53	39.06	28.40	39.93
Close	29.74	35.58	37.62	39.21	43.37		42.61	42.84	41.24	29.74	43.37
Dividends	$ 0.525	$ 0.525	$ 0.525	$ 0.525	$ 0.525	[1]	$ 0.525	$ 0.525	$ 0.525	$ 0.525	$ 0.525	[1]
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	3,928,000,000	4,017,000,000	3,753,000,000	2,739,000,000	2,528,000,000		2,821,000,000	2,455,000,000	2,643,000,000	14,437,000,000	10,447,000,000		10,025,000,000
Operating Income (Loss)	290,000,000	174,000,000	384,000,000	272,000,000	673,000,000		754,000,000	647,000,000	801,000,000	1,120,000,000	2,875,000,000		3,046,000,000
Net Income Loss	137,000,000	91,000,000	166,000,000	168,000,000	447,000,000		386,000,000	443,000,000	495,000,000	558,000,000	1,771,000,000		1,972,000,000
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,290,000,000	1,484,000,000	1,281,000,000	1,388,000,000	1,362,000,000		1,784,000,000	1,444,000,000	1,466,000,000	5,443,000,000	6,056,000,000		6,204,000,000
Operating Income (Loss)	300,000,000	218,000,000	142,000,000	226,000,000	285,000,000		243,000,000	254,000,000	200,000,000	886,000,000	982,000,000		1,056,000,000
Net Income Loss	160,000,000	90,000,000	42,000,000	87,000,000	121,000,000		112,000,000	114,000,000	69,000,000	379,000,000	416,000,000		337,000,000
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	790,000,000	806,000,000	715,000,000	875,000,000	778,000,000		946,000,000	842,000,000	1,153,000,000	3,186,000,000	3,720,000,000		5,519,000,000
Operating Income (Loss)	117,000,000	178,000,000	151,000,000	177,000,000	131,000,000		153,000,000	161,000,000	210,000,000	623,000,000	655,000,000		661,000,000
Net Income Loss	79,000,000	122,000,000	79,000,000	96,000,000	73,000,000		104,000,000	82,000,000	125,000,000	381,000,000	389,000,000		324,000,000
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	703,000,000	720,000,000	616,000,000	696,000,000	673,000,000		745,000,000	674,000,000	976,000,000	2,735,000,000	3,068,000,000		3,541,000,000
Operating Income (Loss)	61,000,000	30,000,000	52,000,000	(11,000,000)	84,000,000		23,000,000	54,000,000	153,000,000	132,000,000	314,000,000		350,000,000
Net Income Loss	$ 15,000,000	$ (4,000,000)	$ 13,000,000	$ (33,000,000)	$ 34,000,000		$ (2,000,000)	$ 13,000,000	$ 78,000,000	$ 4,000,000	$ 136,000,000		$ 147,000,000

[1] 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.