Supplemental Financial Information -Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended					6 Months Ended
	Jun. 30, 2014		Sep. 30, 2013	Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Operating revenues [Abstract]
Total operating revenues	$ 6,024		$ 6,141	$ 6,141		$ 13,261	[1]	$ 12,223	[1]
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	288			271		580		548
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments	0			(21)		(20)		(30)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	68	[2]		47	[2]	111	[2]	84	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	38	[2]		16	[2]	63	[2]	30	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	172			(102)		234		92
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	128			(40)		141		24
Net unrealized income (losses) on pledged assets	10			2		20		3
Regulatory offset to decommissioning trust fund-related activities	(204)	[3]		40	[3]	(299)	[3]	(148)	[4]
Investment income	7			2		8		5
Total decommissioning-related activities	212			(37)		270		85
Long-term lease income	10			5		17		13
Interest income related to uncertain income tax positions	(2)			(1)		7		24
Credit facility termination fees	0			0		0		0
AFUDC - equity	5			5		11		12
Other Income	11					35
Other Expense				9				16
Other, net	243			(17)		348		155
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	3,789			4,070		8,179		7,603
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	118			101		223		194
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments	(1)			(21)		(20)		(30)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	68	[2]		47	[2]	111	[2]	84	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	38	[2]		16	[2]	63	[2]	30	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	172			(102)		234		92
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	128			(40)		141		24
Net unrealized income (losses) on pledged assets	10			2		20		3
Regulatory offset to decommissioning trust fund-related activities	(204)	[3]		40	[3]	(299)	[3]	(148)	[4]
Investment income	7			0		8		(1)
Total decommissioning-related activities	212			(37)		270		85
Interest income related to uncertain income tax positions	3			(2)		17		3
Credit facility termination fees	0			0		0		0
AFUDC - equity	0					0
Other Income	6					23
Other Expense				6				8
Other, net	228			(33)		318		95
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,128			1,080		2,262		2,239
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	72			71		149		145
Decommissioning-Related Activities [Abstract]
Investment income	0					0		0
Interest income related to uncertain income tax positions	0			0		0		0
AFUDC - equity	0			3		3		6
Other Income	5			3		7		5
Other, net	5			6		10		11
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	656			672		1,649		1,567
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	38			39		80		80
Decommissioning-Related Activities [Abstract]
Investment income	(1)			(1)		(1)		(1)
Interest income related to uncertain income tax positions	0					0
AFUDC - equity	1			1		3		2
Other Income	1			0		1		2
Other, net	1			0		3		3
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	653			653		1,707		1,533
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	53			54		113		109
Decommissioning-Related Activities [Abstract]
Investment income	2	[5]		2	[5]	4	[5]	5	[5]
Interest income related to uncertain income tax positions	0					0
AFUDC - equity	3			2		6		4
Other Income	0			0		(1)		0
Other, net	$ 5			$ 4		$ 9		$ 9

[1] For the six months ended June 30, 2014 and 2013, utility taxes of $45 million and $39 million, respectively, are included in revenues and expenses for Generation. For the six months ended June 30, 2014 and 2013, utility taxes of $119 million and $117 million, respectively, are included in revenues and expenses for ComEd. For the six months ended June 30, 2014 and 2013, utility taxes of $65 million and $64 million, respectively, are included in revenues and expenses for PECO. For the six months ended June 30, 2014 and 2013, utility taxes of $43 million and $41 million, respectively, are included in revenues and expenses for BGE.

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

[3] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 – Asset Retirement Obligations of the Exelon 2013 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[4] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 of the Exelon 2013 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

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