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] 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, 2012	$ 21,431														$ 2,982	$ 2,388	$ 593	$ 1	$ 7,323	$ 1,588	$ 0	$ 5,014	$ (1,639)	$ 2,360	$ 2,168	$ 1,360	$ 190	$ 808
Beginning Balance at Dec. 31, 2012	21,730		16,632	(2,327)	9,893	(2,767)	106	193																	2,358
Beginning Balance at Dec. 31, 2012			889,525
Beginning Balance at Dec. 31, 2012									12,665		3,168	8,876	513	108
Net income	1				(4)		1	4	(17)		(18)			1	122		122		(81)				(81)		80			80
Net income on common stock	(4)														121										77
Long-term incentive plan activity			1,067
Long-term incentive plan activity	20		20	0	0
Common stock dividends	(452)				(452)										(83)		(83)		(55)					(55)
Common stock issuance - Constellation merger - Shares
Common stock issuance - Constellation merger - Value
Contribution from parent								0	0			0		0											0
Distribution to members									(211)		(211)
Allocation of tax benefit from members									0			0
Allocation of tax benefit from parent																			172			172
Consolidated VIE dividend to non-controlling interest	(63)						(63)		(63)					(63)
Preferred security dividends	(4)				0			(4)							(1)		(1)								(3)			(3)
Other comprehensive income (loss), net of tax	94	[1]				94			(104)	[1]			(104)		0			0	0
Ending Balance at Mar. 31, 2013	21,089														3,020	2,388	631	1	7,359	1,588	0	5,186	(1,720)	2,305	2,245	1,360	190	885
Ending Balance at Mar. 31, 2013	21,326		16,652	(2,327)	9,437	(2,673)	44	193																	2,435
Ending Balance at Mar. 31, 2013			890,592
Ending Balance at Mar. 31, 2013									$ 12,270		$ 2,939	$ 8,876	$ 409	$ 46

[1] (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.