Supplemental Financial Information -Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Operating revenues [Abstract]
Total operating revenues	$ 6,141		$ 5,966		$ 12,223		$ 10,656
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	271		254		548		448
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					(30)		(79)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	47	[1]	50	[1]	84	[1]	110	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	16	[1]	19	[1]	30	[1]	67	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	(102)		(97)		92		150
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	(40)		(35)		24		30
Net unrealized income (losses) on pledged assets	2		4		3		38
Regulatory offset to decommissioning trust fund-related activities	40	[2]	31	[2]	(148)	[2]	(245)	[2]
Investment income	2		6		5		10
Total decommissioning-related activities	(37)		(28)		85		150
Long-term lease income	5		7		13		15
Interest income related to uncertain income tax positions	(1)		14		24		14
Credit facility termination fees	0		(42)		0		(42)
AFUDC - equity	5		3		12		7
Other Income	9				16
Other Expense			(3)				(2)
Other, net	(17)		(43)		155		152
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	4,070		3,765		7,603		6,508
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	101		90		194		164
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					(30)		(79)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	47	[1]	50	[1]	84	[1]	110	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	16	[1]	19	[1]	30	[1]	67	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	(102)		(97)		92		150
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	(40)		(35)		24		30
Net unrealized income (losses) on pledged assets	2		4		3		38
Regulatory offset to decommissioning trust fund-related activities	40	[2]	31	[2]	(148)	[2]	(245)	[2]
Investment income	0		1		(1)		0
Total decommissioning-related activities	(37)		(28)		85		150
Interest income related to uncertain income tax positions	(2)		0		3		0
Credit facility termination fees	0		(42)		0		(42)
AFUDC - equity	0				0
Other Income	6				8
Other Expense			(7)				(5)
Other, net	(33)		(76)		95		103
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,080		1,281		2,239		2,670
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	71		69		145		144
Decommissioning-Related Activities [Abstract]
Investment income	0				0
Interest income related to uncertain income tax positions	0		1		0		1
AFUDC - equity	3				6		1
Other Income	3		2		5		5
Other, net	6		3		11		7
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	672		715		1,567		1,590
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	39		42		80		74
Decommissioning-Related Activities [Abstract]
Investment income	(1)		1		(1)		2
Interest income related to uncertain income tax positions	0				0
AFUDC - equity	1		1		2		2
Other Income	0				2		1
Other, net	0		2		3		5
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	653		616		1,533		1,312
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	54		47		109		95
Decommissioning-Related Activities [Abstract]
Investment income	2	[3]	3		5	[3]	6	[3]
Interest income related to uncertain income tax positions	0				0
AFUDC - equity	2		3		4		6
Other Income	0		1		0		1
Other, net	$ 4		$ 7		$ 9		$ 13

[1] Includes investment income and realized gains and losses on sales of investments of the trust funds.

[2] Includes the elimination of NDT fund-related activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 13 – Asset Retirement Obligations of the Exelon 2012 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[3] Relates to the cash return on BGE’s rate stabilization deferral. See Note 5 - Regulatory Matters for additional information regarding the rate stabilization deferral.