Supplemental Financial Information -Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Operating revenues [Abstract]
Total operating revenues	$ 6,502	[1]	$ 6,579	[1]	$ 18,725	[2]	$ 17,235	[2]
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	277		290		825		737
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					7		(69)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	138	[3]	33	[3]	221	[3]	143	[3]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	35	[3]	10	[3]	65	[3]	77	[3]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	103		202		196		352
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	46		71		70		101
Net unrealized income (losses) on pledged assets	(9)		22		(5)		60
Regulatory offset to decommissioning trust fund-related activities	(189)	[4]	(208)	[4]	(338)	[4]	(453)	[4]
Investment income	1		5		6		15
Total decommissioning-related activities	124		130		209		280
Long-term lease income	7		7		20		22
Interest income related to uncertain income tax positions	0		0		24		14
Credit facility termination fees	0		(43)		0		(85)
AFUDC - equity	4		4		16		11
Other Income	19				36
Other Expense			(2)				(4)
Other, net	155		101		311		253
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	4,255		4,031		11,858		10,539
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	98		109		292		272
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments					7		(69)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	138	[3]	33	[3]	221	[3]	143	[3]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	35	[3]	10	[3]	65	[3]	77	[3]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	103		202		196		352
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	46		71		70		101
Net unrealized income (losses) on pledged assets	(9)		22		(5)		60
Regulatory offset to decommissioning trust fund-related activities	(189)	[4]	(208)	[4]	(338)	[4]	(453)	[4]
Investment income	0		1		(1)		2
Total decommissioning-related activities	124		130		209		280
Interest income related to uncertain income tax positions	0		1		3		1
Credit facility termination fees	0		(43)		0		(85)
AFUDC - equity	0				0
Other Income	10				18
Other Expense			(6)				(13)
Other, net	134		83		229		185
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,156		1,484		3,395		4,154
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	80		81		225		224
Decommissioning-Related Activities [Abstract]
Investment income	0				0		1
Interest income related to uncertain income tax positions	0		1		0		1
AFUDC - equity	2		1		8		2
Other Income	5		3		10		8
Other, net	7		5		18		12
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	728		806		2,295		2,396
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	41		48		121		122
Decommissioning-Related Activities [Abstract]
Investment income	0		0		(1)		2
Interest income related to uncertain income tax positions	0				1
AFUDC - equity	1		1		3		3
Other Income	0		1		1		1
Other, net	1		2		4		6
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	737		720		2,271		2,032
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	53		48		162		143
Decommissioning-Related Activities [Abstract]
Investment income	2	[5]	3		7	[5]	9	[5]
Interest income related to uncertain income tax positions	0				0
AFUDC - equity	1		2		5		8
Other Income	1		0		1		1
Other, net	$ 4		$ 5		$ 13		$ 18

[1] For the three months ended September 30, 2013 and 2012, utility taxes of $21 million and $28 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2013 and 2012, utility taxes of $65 million and $67 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2013 and 2012, utility taxes of $33 million and $40 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2013 and 2012, utility taxes of $20 million and $20 million, respectively, are included in revenues and expenses for BGE.

[2] For the nine months ended September 30, 2013 and 2012, utility taxes of $60 million and $60 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2013 and 2012, utility taxes of $182 million and $182 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2013 and 2012, utility taxes of $97 million and $108 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2013 and period of March 12, 2012 through September 30, 2012, utility taxes of $62 million and $42 million, respectively, are included in revenues and expenses for BGE.

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

[4] 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.

[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.