Consolidated Statement of Changes in Shareholders Equity (Unaudited) (USD $) Share data in Thousands	Total	Common Stock [Member]	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive (Loss) Income, Net	Noncontrolling Interest	BGE preference stock not subject to mandatory redemption	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
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	200,000,000			202,000,000		(2,000,000)		166,000,000	168,000,000			(2,000,000)	97,000,000		97,000,000		87,000,000				87,000,000		(30,000,000)			(30,000,000)
Net income on common stock	200,000,000							168,000,000					96,000,000										(33,000,000)
Long-term incentive plan activity		917
Appropriation of retained earnings for future dividends																	0				(87,000,000)	87,000,000
Long-term incentive plan activity	40,000,000	40,000,000	0	0
Common stock dividends	(425,000,000)			(425,000,000)									(87,000,000)		(87,000,000)		(75,000,000)					(75,000,000)
Common stock issuance - Constellation merger - Shares		188,124
Common stock issuance - Constellation merger - Value	7,365,000,000	7,365,000,000
Acquisition of Constellation - Members Equity	285,000,000					92,000,000	193,000,000	5,363,000,000		5,272,000,000		91,000,000
Distribution to members								(600,000,000)	(600,000,000)
Allocation of tax benefit from member								0		0							9,000,000			9,000,000
Allocation of tax benefit from parent													0	0
Preferred security dividends	2,000,000			2,000,000									(1,000,000)		(1,000,000)								(3,000,000)			(3,000,000)
Repayment of receivable from parent													0
Other comprehensive income (loss), net of tax					251,000,000			252,000,000			252,000,000					1,000,000	1,000,000		1,000,000
Ending Balance at Mar. 31, 2012	21,816,000,000												2,948,000,000	2,379,000,000	568,000,000	1,000,000	7,059,000,000	1,588,000,000	0	5,012,000,000	(1,639,000,000)	2,098,000,000	2,078,000,000	1,294,000,000	190,000,000	784,000,000
Ending Balance at Mar. 31, 2012	22,102,000,000	16,512,000,000	(2,327,000,000)	9,830,000,000	(2,199,000,000)	93,000,000	193,000,000																2,268,000,000
Ending Balance at Mar. 31, 2012		887,153
Ending Balance at Mar. 31, 2012								$ 13,889,000,000	$ 3,800,000,000	$ 8,828,000,000	$ 1,167,000,000	$ 94,000,000