Consolidated Statement of Changes in Shareholders Equity (Unaudited) (USD $)	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] 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] Common Stock [Member]	Baltimore Gas and Electric Company [Member] Nonredeemable Preferred Stock [Member]	Baltimore Gas and Electric Company [Member] Retained Earnings
Beginning Balance at Dec. 31, 2011	$ 14,385,000,000												$ 2,938,000,000	$ 2,379,000,000	$ 559,000,000		$ 7,037,000,000	$ 1,588,000,000	$ (1,000,000)	$ 5,003,000,000	$ (1,639,000,000)	$ 2,086,000,000	$ 2,111,000,000	$ 1,294,000,000	$ 190,000,000	$ 817,000,000
Beginning 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																	2,301,000,000
Beginning Balance at Dec. 31, 2011		698,112,000
Beginning Balance at Dec. 31, 2011								8,708,000,000	4,232,000,000	3,556,000,000	915,000,000	5,000,000
Net income	787,000,000			782,000,000		(6,000,000)	11,000,000	419,000,000	425,000,000			(6,000,000)	300,000,000		300,000,000		219,000,000				219,000,000		(14,000,000)			(14,000,000)
Net income on common stock	782,000,000												297,000,000										(24,000,000)
Long-term incentive plan activity		2,790,000
Appropriation of retained earnings for future dividends																	0				(219,000,000)	219,000,000
Long-term incentive plan activity	122,000,000	122,000,000	0	0
Common stock dividends	(878,000,000)			(878,000,000)									(258,000,000)		(258,000,000)		(95,000,000)					(95,000,000)
Common stock issuance - Constellation merger - Shares		188,124,000
Common stock issuance - Constellation merger - Value	7,365,000,000	7,365,000,000
Contribution from parent	92,000,000					92,000,000	0	5,258,000,000		5,258,000,000		0											66,000,000
Distribution to members								(1,384,000,000)	(1,384,000,000)
Allocation of tax benefit from members								0		0
Allocation of tax benefit from parent																	13,000,000			13,000,000
BGE preference stock acquired	193,000,000						193,000,000
Preferred security dividends	(11,000,000)			0			(11,000,000)						(3,000,000)		(3,000,000)								(10,000,000)			(10,000,000)
Other comprehensive income (loss), net of tax	45,000,000				45,000,000			(163,000,000)			(163,000,000)		1,000,000			1,000,000	1,000,000		1,000,000
Ending Balance at Sep. 30, 2012	21,821,000,000												2,978,000,000	2,379,000,000	598,000,000	1,000,000	7,175,000,000	1,588,000,000	0	5,016,000,000	(1,639,000,000)	2,210,000,000	2,153,000,000	1,360,000,000	190,000,000	793,000,000
Ending Balance at Sep. 30, 2012	22,103,000,000	16,594,000,000	(2,327,000,000)	9,959,000,000	(2,405,000,000)	89,000,000	193,000,000																2,343,000,000
Ending Balance at Sep. 30, 2012		889,026,000
Ending Balance at Sep. 30, 2012								12,930,000,000	3,273,000,000	8,814,000,000	752,000,000	91,000,000
Beginning Balance at Jun. 30, 2012
Net income	297,000,000							87,000,000					123,000,000				90,000,000						0
Net income on common stock	296,000,000												122,000,000										(4,000,000)
Other comprehensive income (loss), net of tax	(92,000,000)							(152,000,000)					0				0
Ending Balance at Sep. 30, 2012	21,821,000,000												2,978,000,000	2,379,000,000			7,175,000,000	1,588,000,000					2,153,000,000	1,360,000,000	190,000,000
Ending Balance at Sep. 30, 2012	22,103,000,000																						2,343,000,000
Ending Balance at Sep. 30, 2012								$ 12,930,000,000