Consolidated Statement of Changes in Shareholders Equity (Unaudited) (USD $) Share data in Thousands	Total	Common Stock	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive (Loss) Income, Net	Noncontrolling Interest	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member] Undistributed Earnings [Member]	Exelon Generation Co L L C [Member] Membership Interest [Member]	Exelon Generation Co L L C [Member] Accumulated Other Comprehensive (Loss) Income, Net	Exelon Generation Co L L C [Member] Noncontrolling Interest	PECO Energy Co [Member]	PECO Energy Co [Member] Common Stock	PECO Energy Co [Member] Receivable From Parent [Member]	PECO Energy Co [Member] Retained Earnings	PECO Energy Co [Member] Accumulated Other Comprehensive (Loss) Income, Net	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member] Common Stock	Commonwealth Edison Co [Member] Accumulated Other Comprehensive (Loss) Income, Net	Commonwealth Edison Co [Member] Other Paid-In Capital	Commonwealth Edison Co [Member] Retained Deficit Unappropriated	Commonwealth Edison Co [Member] Retained Earnings Appropriated
Beginning Balance at Dec. 31, 2008												$ 2,182,000,000	$ 2,291,000,000	$ (500,000,000)	$ 389,000,000	$ 2,000,000	$ 6,735,000,000	$ 1,588,000,000	$ (5,000,000)	$ 4,982,000,000	$ (1,639,000,000)	$ 1,809,000,000
Beginning Balance at Dec. 31, 2008	11,047,000,000	8,816,000,000	(2,338,000,000)	6,820,000,000	(2,251,000,000)	0
Beginning Balance at Dec. 31, 2008		692,953
Beginning Balance at Dec. 31, 2008							6,566,000,000	2,323,000,000	3,407,000,000	835,000,000	1,000,000
Net income	2,707,000,000			2,707,000,000			2,122,000,000	2,122,000,000				353,000,000			353,000,000		374,000,000				374,000,000
Long-term incentive plan activity		1,088
Employee stock purchase plan issuances		524
Appropriation of retained earnings for future dividends																	0				(374,000,000)	374,000,000
Long-term incentive plan activity	90,000,000	85,000,000	10,000,000	(5,000,000)
Employee stock purchase plan issuances	22,000,000	22,000,000
Common stock dividends	(1,388,000,000)			(1,388,000,000)								(312,000,000)			(312,000,000)		(240,000,000)					(240,000,000)
Distribution to members							(2,276,000,000)	(2,276,000,000)
Allocation of tax benefit from member							57,000,000		57,000,000
Transfer of AmerGen pension and non-pension postretirement benefit plans to Exelon, net of income taxes							20,000,000			20,000,000
Allocation of tax benefit from parent												27,000,000	27,000,000				8,000,000			8,000,000
Preferred security dividends												(4,000,000)			(4,000,000)
Repayment of receivable from parent												320,000,000		320,000,000
Other comprehensive income (loss), net of tax	162,000,000				162,000,000		302,000,000			302,000,000		(1,000,000)				(1,000,000)	5,000,000		5,000,000
Noncontrolling interest in income of consolidated entity							1,000,000				1,000,000
Ending Balance at Dec. 31, 2009												2,565,000,000	2,318,000,000	(180,000,000)	426,000,000	1,000,000	6,882,000,000	1,588,000,000	0	4,990,000,000	(1,639,000,000)	1,943,000,000
Ending Balance at Dec. 31, 2009	12,640,000,000	8,923,000,000	(2,328,000,000)	8,134,000,000	(2,089,000,000)
Ending Balance at Dec. 31, 2009		694,565
Ending Balance at Dec. 31, 2009							6,792,000,000	2,169,000,000	3,464,000,000	1,157,000,000	2,000,000
Net income	749,000,000						561,000,000					100,000,000					116,000,000
Ending Balance at Mar. 31, 2010
Beginning Balance at Dec. 31, 2009												2,565,000,000	2,318,000,000	(180,000,000)	426,000,000	1,000,000	6,882,000,000	1,588,000,000	0	4,990,000,000	(1,639,000,000)	1,943,000,000
Beginning Balance at Dec. 31, 2009	12,640,000,000	8,923,000,000	(2,328,000,000)	8,134,000,000	(2,089,000,000)	0
Beginning Balance at Dec. 31, 2009		694,565
Beginning Balance at Dec. 31, 2009							6,792,000,000	2,169,000,000	3,464,000,000	1,157,000,000	2,000,000
Net income	2,563,000,000			2,563,000,000			1,972,000,000	1,972,000,000				324,000,000			324,000,000		337,000,000				337,000,000
Long-term incentive plan activity		1,380
Employee stock purchase plan issuances		644
Appropriation of retained earnings for future dividends																	0				(337,000,000)	337,000,000
Long-term incentive plan activity	60,000,000	60,000,000	1,000,000	(1,000,000)
Employee stock purchase plan issuances	23,000,000	23,000,000
Common stock dividends	(1,392,000,000)			(1,392,000,000)								(224,000,000)			(224,000,000)		(310,000,000)				(310,000,000)
Distribution to members							(1,508,000,000)	(1,508,000,000)
Allocation of tax benefit from member							62,000,000		62,000,000
Allocation of tax benefit from parent												43,000,000	43,000,000				2,000,000			2,000,000
Preferred security dividends												(4,000,000)			(4,000,000)
Repayment of receivable from parent												180,000,000		180,000,000
Acquisition of Exelon Wind	3,000,000					3,000,000	3,000,000				3,000,000
Other comprehensive income (loss), net of tax	(334,000,000)				(334,000,000)		(144,000,000)			(144,000,000)		(1,000,000)				(1,000,000)	(1,000,000)		(1,000,000)
Ending Balance at Dec. 31, 2010	13,560,000,000											2,883,000,000	2,361,000,000	0	522,000,000	0	6,910,000,000	1,588,000,000	(1,000,000)	4,992,000,000	(1,639,000,000)	1,970,000,000
Ending Balance at Dec. 31, 2010	13,563,000,000	9,006,000,000	(2,327,000,000)	9,304,000,000	(2,423,000,000)	3,000,000
Ending Balance at Dec. 31, 2010		696,589
Ending Balance at Dec. 31, 2010							7,177,000,000	2,633,000,000	3,526,000,000	1,013,000,000	5,000,000
Beginning Balance at Sep. 30, 2010
Net income	524,000,000						424,000,000					20,000,000					91,000,000
Ending Balance at Dec. 31, 2010	13,560,000,000											2,883,000,000					6,910,000,000	1,588,000,000
Ending Balance at Dec. 31, 2010	13,563,000,000
Ending Balance at Dec. 31, 2010							7,177,000,000
Net income	668,000,000						495,000,000					125,000,000					69,000,000
Ending Balance at Mar. 31, 2011
Beginning Balance at Dec. 31, 2010	13,560,000,000											2,883,000,000	2,361,000,000	0	522,000,000		6,910,000,000	1,588,000,000	(1,000,000)	4,992,000,000	(1,639,000,000)	1,970,000,000
Beginning Balance at Dec. 31, 2010	13,563,000,000	9,006,000,000	(2,327,000,000)	9,304,000,000	(2,423,000,000)
Beginning Balance at Dec. 31, 2010		696,589
Beginning Balance at Dec. 31, 2010							7,177,000,000	2,633,000,000	3,526,000,000	1,013,000,000	5,000,000
Net income	2,495,000,000			2,495,000,000			1,771,000,000	1,771,000,000				389,000,000			389,000,000		416,000,000				416,000,000
Long-term incentive plan activity		861
Employee stock purchase plan issuances		662
Appropriation of retained earnings for future dividends																	0				(416,000,000)	416,000,000
Long-term incentive plan activity	76,000,000	76,000,000	0	0
Employee stock purchase plan issuances	25,000,000	25,000,000
Common stock dividends	(1,744,000,000)			(1,744,000,000)								(348,000,000)			(348,000,000)		(300,000,000)					(300,000,000)
Distribution to members							(172,000,000)	(172,000,000)
Allocation of tax benefit from member							30,000,000		30,000,000
Allocation of tax benefit from parent												18,000,000	18,000,000				11,000,000			11,000,000
Preferred security dividends												(4,000,000)			(4,000,000)
Repayment of receivable from parent												0		0
Acquisition of Exelon Wind							0				0
Other comprehensive income (loss), net of tax	(27,000,000)				(27,000,000)		(98,000,000)			(98,000,000)		0					0		0
Ending Balance at Dec. 31, 2011	14,385,000,000											2,938,000,000	2,379,000,000	0	559,000,000	0	7,037,000,000	1,588,000,000	(1,000,000)	5,003,000,000	(1,639,000,000)	2,086,000,000
Ending Balance at Dec. 31, 2011	14,388,000,000	9,107,000,000	(2,327,000,000)	10,055,000,000	(2,450,000,000)	3,000,000
Ending Balance at Dec. 31, 2011		698,112
Ending Balance at Dec. 31, 2011							8,708,000,000	4,232,000,000	3,556,000,000	915,000,000	5,000,000
Beginning Balance at Sep. 30, 2011
Net income	606,000,000						446,000,000					73,000,000					121,000,000
Ending Balance at Dec. 31, 2011	14,385,000,000											2,938,000,000				0	7,037,000,000	1,588,000,000
Ending Balance at Dec. 31, 2011	14,388,000,000					3,000,000
Ending Balance at Dec. 31, 2011							$ 8,708,000,000