Segment Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Segment Reporting Information [Line Items]
Total revenues	$ 18,924,000,000		$ 18,644,000,000		$ 17,318,000,000
Intersegment revenues	9,000,000		6,000,000		9,000,000
Depreciation and amortization	1,335,000,000		2,075,000,000		1,834,000,000
Operating Expenses	14,444,000,000		13,918,000,000		12,568,000,000
Interest expense (in total) - Segment Reporting	726,000,000		817,000,000		731,000,000
Income (loss) from continuing operations before income taxes	3,952,000,000		4,221,000,000		4,419,000,000
Income taxes	1,457,000,000		1,658,000,000		1,712,000,000
Net income (loss)	2,495,000,000		2,563,000,000		2,707,000,000
Capital expenditures	4,042,000,000		3,326,000,000		3,273,000,000
Total assets	55,092,000,000		52,240,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	9,000,000		6,000,000		9,000,000
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	443,000,000	[1]	476,000,000	[1]	481,000,000	[1]
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Total revenues	10,308,000,000		10,025,000,000		9,703,000,000
Intersegment revenues	1,161,000,000		3,102,000,000		3,472,000,000
Depreciation and amortization	570,000,000		474,000,000		333,000,000
Operating Expenses	7,432,000,000		6,979,000,000		6,408,000,000
Interest expense (in total) - Segment Reporting	170,000,000		153,000,000		113,000,000
Income (loss) from continuing operations before income taxes	2,827,000,000		3,150,000,000		3,555,000,000
Income taxes	1,056,000,000		1,178,000,000		1,433,000,000
Net income (loss)	1,771,000,000		1,972,000,000		2,122,000,000
Capital expenditures	2,491,000,000		1,883,000,000		1,977,000,000
Total assets	27,433,000,000		24,534,000,000
Revenues net of purchased power and fuel expense	6,858,000,000		6,562,000,000		6,771,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	1,161,000,000		3,102,000,000		3,472,000,000
Segment Reporting Additional Narrative Information [Abstract]
SO2 emissions allowance impairment			57,000,000
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Total revenues	3,967,000,000		3,246,000,000		3,195,000,000
Intersegment revenues	508,000,000		2,092,000,000		2,016,000,000
Revenues net of purchased power and fuel expense	3,359,000,000		2,512,000,000		2,578,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	508,000,000		2,092,000,000		2,016,000,000
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Total revenues	5,344,000,000		5,762,000,000		5,538,000,000
Intersegment revenues	653,000,000		1,010,000,000		1,456,000,000
Revenues net of purchased power and fuel expense	3,547,000,000		4,081,000,000		4,148,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	653,000,000		1,010,000,000		1,456,000,000
Generation South and West [Member]
Segment Reporting Information [Line Items]
Total revenues	776,000,000		692,000,000		714,000,000
Revenues net of purchased power and fuel expense	70,000,000		(131,000,000)		(117,000,000)
Generation Other Activity [Member]
Segment Reporting Information [Line Items]
Total revenues	221,000,000		325,000,000		256,000,000
Revenues net of purchased power and fuel expense	(118,000,000)		100,000,000		162,000,000
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Total revenues	6,056,000,000		6,204,000,000		5,774,000,000
Intersegment revenues	2,000,000		2,000,000		2,000,000
Depreciation and amortization	542,000,000		516,000,000		494,000,000
Operating Expenses	5,074,000,000		5,148,000,000		4,931,000,000
Interest expense (in total) - Segment Reporting	345,000,000		386,000,000		319,000,000
Income (loss) from continuing operations before income taxes	666,000,000		694,000,000		603,000,000
Income taxes	250,000,000		357,000,000		229,000,000
Net income (loss)	416,000,000		337,000,000		374,000,000
Capital expenditures	1,028,000,000		962,000,000		854,000,000
Total assets	22,653,000,000		21,652,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	2,000,000		2,000,000		2,000,000
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	243,000,000		205,000,000		232,000,000
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Total revenues	3,720,000,000		5,519,000,000		5,311,000,000
Intersegment revenues	5,000,000		5,000,000		6,000,000
Depreciation and amortization	202,000,000		1,060,000,000		952,000,000
Operating Expenses	3,065,000,000		4,858,000,000		4,614,000,000
Interest expense (in total) - Segment Reporting	134,000,000		193,000,000		187,000,000
Income (loss) from continuing operations before income taxes	535,000,000		476,000,000		499,000,000
Income taxes	146,000,000		152,000,000		146,000,000
Net income (loss)	389,000,000		324,000,000		353,000,000
Capital expenditures	481,000,000		545,000,000		388,000,000
Total assets	9,156,000,000		8,985,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	5,000,000		5,000,000		6,000,000
Segment Reporting Additional Narrative Information [Abstract]
Utility Taxes	173,000,000		271,000,000		249,000,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	830,000,000		755,000,000		757,000,000
Intersegment revenues	831,000,000		756,000,000		756,000,000
Depreciation and amortization	21,000,000		25,000,000		55,000,000
Operating Expenses	863,000,000		792,000,000		840,000,000
Interest expense (in total) - Segment Reporting	77,000,000		85,000,000		112,000,000
Income (loss) from continuing operations before income taxes	(63,000,000)		(91,000,000)		(235,000,000)
Income taxes	9,000,000		(27,000,000)		(102,000,000)
Net income (loss)	(72,000,000)		(64,000,000)		(133,000,000)
Capital expenditures	42,000,000		14,000,000		54,000,000
Total assets	6,244,000,000		6,651,000,000
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	831,000,000		756,000,000		756,000,000
Business Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(1,990,000,000)		(3,859,000,000)		(4,227,000,000)
Intersegment revenues	(1,990,000,000)		(3,859,000,000)		(4,227,000,000)
Operating Expenses	(1,990,000,000)		(3,859,000,000)		(4,225,000,000)
Income (loss) from continuing operations before income taxes	(13,000,000)		(8,000,000)		(3,000,000)
Income taxes	(4,000,000)		(2,000,000)		6,000,000
Net income (loss)	(9,000,000)		(6,000,000)		(9,000,000)
Capital expenditures	0		(78,000,000)		0
Total assets	(10,394,000,000)		(9,582,000,000)
Segment Reporting Intersegment Revenue [Abstract]
Intersegment revenues	$ (1,990,000,000)		$ (3,859,000,000)		$ (4,227,000,000)

[1] Generation's utility tax represents gross receipts tax related to its retail operations and ComEd's and PECO's utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues, respectively. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants' Consolidated Statements of Operations.