Consolidated Statement of Changes in Shareholders Equity (Unaudited) (USD $) In Millions, except Share data in Thousands	Total	Common Stock [Member]	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive (Loss) Income, Net	Noncontrolling Interest	Preference Stock Not Subject To Mandatory Redemption [Member]	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 [Member]	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 [Member]	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	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member] Undistributed Earnings [Member]	Baltimore Gas and Electric Company [Member] Common Stock [Member]	Baltimore Gas and Electric Company [Member] Membership Interest [Member]	Baltimore Gas and Electric Company [Member] Noncontrolling Interest	Baltimore Gas and Electric Company [Member] Preference Stock Not Subject To Mandatory Redemption [Member]
Beginning Balance at Dec. 31, 2009													$ 2,565.00	$ 2,318.00	$ (180.00)	$ 426.00	$ 1.00	$ 6,882.00	$ 1,588.00	$ 0	$ 4,990.00	$ (1,639.00)	$ 1,943.00		$ 645.00	$ 1,294.00	$ 1,939.00
Beginning Balance at Dec. 31, 2009	12,640.00	8,923.00	(2,328.00)	8,134.00	(2,089.00)																			2,147.00				18.00	190.00
Beginning Balance at Dec. 31, 2009		694,565
Beginning Balance at Dec. 31, 2009								6,792.00	2,169.00	3,464.00	1,157.00	2.00
Net income	2,563.00			2,563.00				1,972.00	1,972.00				324.00			324.00		337.00				337.00		147.00	147.00		147.00
Net income on common stock	2,563.00												320.00											134.00
Long-term incentive plan activity		1,380
Employee stock purchase plan issuances		644
Appropriation of retained earnings for future dividends																		0				(337.00)	337.00
Long-term incentive plan activity	60.00	60.00	1.00	(1.00)
Employee stock purchase plan issuances	23.00	23.00
Common stock dividends	(1,392.00)			(1,392.00)									(224.00)			(224.00)		(310.00)					(310.00)
Distribution to members								(1,508.00)	(1,508.00)
Allocation of tax benefit from members								62.00		62.00
Transfer of AmerGen pension and non-pension postretirement benefit plans to Exelon, net of income taxes								3.00
Allocation of tax benefit from parent													43.00	43.00				2.00			2.00
Preferred security dividends													(4.00)			(4.00)								13.00	13.00		13.00
Repayment of receivable from parent													180.00		180.00
Acquisition of Exelon Wind	3.00					3.00						3.00
Other comprehensive income (loss), net of tax	(334.00)				(334.00)			(144.00)			(144.00)		(1.00)				(1.00)	(1.00)		(1.00)
Sale of noncontrolling interest																								(18.00)				(18.00)
Ending Balance at Dec. 31, 2010													2,883.00	2,361.00	0	522.00	0	6,910.00	1,588.00	(1.00)	4,992.00	(1,639.00)	1,970.00		779.00	1,294.00	2,073.00
Ending Balance at Dec. 31, 2010	13,563.00	9,006.00	(2,327.00)	9,304.00	(2,423.00)	3.00																		2,263.00				0	190.00
Ending Balance at Dec. 31, 2010		696,589
Ending Balance at Dec. 31, 2010								7,177.00	2,633.00	3,526.00	1,013.00	5.00
Net income	668.00							495.00					125.00					69.00						78.00
Ending Balance at Mar. 31, 2011
Beginning Balance at Dec. 31, 2010													2,883.00	2,361.00	0	522.00	0	6,910.00	1,588.00	(1.00)	4,992.00	(1,639.00)	1,970.00		779.00	1,294.00	2,073.00
Beginning Balance at Dec. 31, 2010	13,563.00	9,006.00	(2,327.00)	9,304.00	(2,423.00)																			2,263.00					190.00
Beginning Balance at Dec. 31, 2010		696,589
Beginning Balance at Dec. 31, 2010								7,177.00	2,633.00	3,526.00	1,013.00
Net income	2,499.00			2,495.00			4.00	1,771.00	1,771.00				389.00			389.00		416.00				416.00		136.00	136.00		136.00
Net income on common stock	2,495.00												385.00											123.00
Long-term incentive plan activity		861
Employee stock purchase plan issuances		662
Appropriation of retained earnings for future dividends																		0				(416.00)	416.00
Long-term incentive plan activity	76.00	76.00	0	0
Employee stock purchase plan issuances	25.00	25.00
Common stock dividends	(1,744.00)			(1,744.00)									(348.00)			(348.00)		(300.00)					(300.00)	(85.00)	(85.00)		(85.00)
Contribution from parent																								0
Distribution to members								(172.00)	(172.00)
Allocation of tax benefit from members								30.00		30.00
Allocation of tax benefit from parent													18.00	18.00				11.00			11.00
Preferred security dividends	4.00						4.00						(4.00)			(4.00)								(13.00)	(13.00)		(13.00)
Repayment of receivable from parent													0		0
Acquisition of Exelon Wind	0
Other comprehensive income (loss), net of tax	(27.00)				(27.00)			(98.00)			(98.00)		0				0	0		0
Ending Balance at Dec. 31, 2011	14,385.00												2,938.00	2,379.00	0	559.00	0	7,037.00	1,588.00	(1.00)	5,003.00	(1,639.00)	2,086.00	2,111.00	817.00		2,111.00
Ending Balance at Dec. 31, 2011	14,388.00	9,107.00	(2,327.00)	10,055.00	(2,450.00)																			2,301.00				0	190.00
Ending Balance at Dec. 31, 2011		698,112
Ending Balance at Dec. 31, 2011								8,708.00	4,232.00	3,556.00	915.00
Beginning Balance at Sep. 30, 2011
Net income	606.00							447.00					73.00					121.00						34.00
Ending Balance at Dec. 31, 2011	14,385.00												2,938.00					7,037.00	1,588.00					2,111.00
Ending Balance at Dec. 31, 2011	14,388.00																							2,301.00				0	190.00
Ending Balance at Dec. 31, 2011								8,708.00
Net income	200.00							168.00					96.00					87.00						(33.00)
Ending Balance at Mar. 31, 2012
Beginning Balance at Dec. 31, 2011	14,385.00												2,938.00	2,379.00	0	559.00	0	7,037.00	1,588.00	(1.00)	5,003.00	(1,639.00)	2,086.00	2,111.00	817.00	1,294.00	2,111.00
Beginning Balance at Dec. 31, 2011	14,388.00	9,107.00	(2,327.00)	10,055.00	(2,450.00)	3.00																		2,301.00				0	190.00
Beginning Balance at Dec. 31, 2011		698,112
Beginning Balance at Dec. 31, 2011								8,708.00	4,232.00	3,556.00	915.00	5.00
Net income	1,171.00			1,160.00		(3.00)	14.00	558.00	562.00				381.00			381.00		379.00				379.00		4.00	4.00		4.00
Net income on common stock	1,160.00												377.00											(9.00)
Long-term incentive plan activity		2,432
Employee stock purchase plan issuances	857
Appropriation of retained earnings for future dividends																		0				(379.00)	379.00
Long-term incentive plan activity	126.00	126.00	0	0
Employee stock purchase plan issuances	26.00	26.00
Common stock dividends	(1,322.00)			(1,322.00)									(343.00)			(343.00)		(105.00)					(105.00)
Common stock issuance - Constellation merger - Shares	188,124
Common stock issuance - Constellation merger - Value	7,365.00	7,365.00						5,264.00		5,264.00
Contribution from parent																								66.00		66.00	66.00
Distribution to members								(1,626.00)	(1,626.00)
Allocation of tax benefit from members								48.00		48.00
Allocation of tax benefit from parent													9.00	9.00				11.00			11.00
BGE preference stock acquired	193.00						193.00
Preferred security dividends	14.00						14.00						(4.00)			(4.00)								(13.00)	(13.00)		(13.00)
Repayment of receivable from parent													0		0
Acquisition of Exelon Wind								115.00		8.00		107.00
Noncontrolling interest acquired	114.00	8.00				106.00
Other comprehensive income (loss), net of tax	(317.00)				(317.00)			(402.00)			(402.00)		1.00				1.00	1.00		1.00
Noncontrolling interest in income of consolidated entity												(4.00)
Ending Balance at Dec. 31, 2012	21,431.00												2,982.00	2,388.00	0	593.00	1.00	7,323.00	1,588.00	0	5,014.00	(1,639.00)	2,360.00	2,168.00	808.00	1,360.00	2,168.00
Ending Balance at Dec. 31, 2012	21,730.00	16,632.00	(2,327.00)	9,893.00	(2,767.00)	106.00																		2,358.00				0	190.00
Ending Balance at Dec. 31, 2012		889,525
Ending Balance at Dec. 31, 2012							193.00	12,665.00	3,168.00	8,876.00	513.00	108.00
Beginning Balance at Sep. 30, 2012
Net income	378.00							137.00					79.00					160.00						15.00
Ending Balance at Dec. 31, 2012	21,431.00												2,982.00					7,323.00	1,588.00					2,168.00
Ending Balance at Dec. 31, 2012	21,730.00																							2,358.00				0	190.00
Ending Balance at Dec. 31, 2012								$ 12,665.00