Supplemental Financial Information -Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Operating revenues [Abstract]
Total operating revenues	$ 6,163	$ 6,502	$ 6,141	$ 6,082	$ 6,254	$ 6,579	$ 5,966	$ 4,690	$ 24,888		$ 23,489		$ 19,063
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									449	[1]	463	[1]	443	[1]
Taxes other than income - real estate									302		227		177
Taxes other than income - payroll									159		131		123
Taxes other than income - other									185		198		42
Total taxes other than income									1,095		1,019		785
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments									10		(91)		(1)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units									256	[2]	189	[2]	177	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units									77	[2]	102	[2]	45	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units									406		386		(74)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement									146		105		(4)
Net unrealized income (losses) on pledged assets									7		73		48
Regulatory offset to decommissioning trust fund-related activities									(546)	[3]	(530)	[3]	(130)	[3]
Investment income									8		20		10
Total decommissioning-related activities									346		325		62
Long-term lease income									28		29		28
Interest income related to uncertain income tax positions									24		15		53
Income related to termination of a gas supply guarantee													0
Losses on early retirement of debt											0		0
Other-than-temporary impairment to Rabbi trust investments											0
Credit facility termination fees									0		(85)
AFUDC - equity									22		17		17
Bargain purchase gain related to Wolf Hollow acquisition													36
Realized gains on Rabbi Trust investments											0		0
Other Income									45		25
Other Expense													(3)
Other, net									473		346		203
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	3,772	4,255	4,070	3,533	3,898	4,031	3,765	2,743	15,630		14,437		10,447
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									79	[1]	82		27
Taxes other than income - real estate									205		189		146
Taxes other than income - payroll									89		78		71
Taxes other than income - other									16		20		20
Total taxes other than income									389		369		264
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments									10		(91)		(1)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units									256	[2]	189	[2]	177	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units									77	[2]	102	[2]	45	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units									406		386		(74)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement									146		105		(4)
Net unrealized income (losses) on pledged assets									7				48
Regulatory offset to decommissioning trust fund-related activities									(546)	[3]	(530)	[3]	(130)	[3]
Investment income									(1)		3		1
Total decommissioning-related activities									346		325		62
Interest income related to uncertain income tax positions									4		2		31
Income related to termination of a gas supply guarantee													0
Losses on early retirement of debt											0		0
Credit facility termination fees									0		(85)
Bargain purchase gain related to Wolf Hollow acquisition													36
Other Income									19		(6)
Other Expense													(8)
Other, net									368		239		122
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,068	1,156	1,080	1,160	1,290	1,484	1,281	1,388	4,464		5,443		6,056
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									241	[1]	239	[1]	243	[1]
Taxes other than income - real estate									24		22		22
Taxes other than income - payroll									27		26		25
Taxes other than income - other									7		8		6
Total taxes other than income									299		295		296
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments									0		0		0
Decommissioning-Related Activities [Abstract]
Investment income									0		1		1
Interest income related to uncertain income tax positions									0		20		14
Other-than-temporary impairment to Rabbi trust investments											0
AFUDC - equity									11		6		8
Realized gains on Rabbi Trust investments											0		0
Other Income									15		12		(6)
Other, net									26		39		29
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	805	728	672	895	790	806	715	875	3,100		3,186		3,720
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									129	[1]	141	[1]	173	[1]
Taxes other than income - real estate									14		13		9
Taxes other than income - payroll									13		12		13
Taxes other than income - other									2		(4)		10
Total taxes other than income									158		162		205
Decommissioning-Related Activities [Abstract]
Investment income									(1)		2		3
Interest income related to uncertain income tax positions									0		0		1
AFUDC - equity									4		4		9
Other Income									3		2		(1)
Other, net									6		8		14
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	794	737	653	880	703	720	616	697	3,065		2,735		3,068
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									82		75		79
Taxes other than income - real estate									112		111		107
Taxes other than income - payroll									15		18		17
Taxes other than income - other									4		4		4
Total taxes other than income									213		208		207
Decommissioning-Related Activities [Abstract]
Investment income									9	[4]	11	[4]	13	[4]
AFUDC - equity									7		10		15
Other Income									1		2
Other Expense													(2)
Other, net									$ 17		$ 23		$ 26

[1] Generation's utility tax represents gross receipts tax related to its retail operations and ComEd's, PECO's and BGE’s utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues, respectively. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants' Consolidated Statements of Operations

[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 for additional information regarding the accounting for nuclear decommissioning.

[4] (c)        Relates to the cash return on BGE’s rate stabilization deferral. See Note 3 – Regulatory Matters for additional information regarding the rate stabilization deferral.