Supplemental Financial Information -Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Operating revenues [Abstract]
Total operating revenues	$ 7,237	[1]	$ 6,082	[1]
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	293		277
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments	(19)		(9)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	43	[2]	36	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	25	[2]	14	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	61		195
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	13		64
Net unrealized income (losses) on pledged assets	10		2
Regulatory offset to decommissioning trust fund-related activities	(94)	[3]	(190)	[3]
Investment income	1		3
Total decommissioning-related activities	58		121
Long-term lease income	6		8
Interest income related to uncertain income tax positions	10		25
AFUDC - equity	6		6
Other Income	22		9
Other, net	103		172
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	4,390		3,533
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	105		93
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments	(19)		(9)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	43	[2]	36	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	25	[2]	14	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	61		195
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	13		64
Net unrealized income (losses) on pledged assets	10		2
Regulatory offset to decommissioning trust fund-related activities	(94)	[3]	(190)	[3]
Investment income	1		(2)
Total decommissioning-related activities	58		121
Interest income related to uncertain income tax positions	14		5
Other Income	17		4
Other, net	90		128
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,134		1,160
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	77		74
Decommissioning-Related Activities [Abstract]
Investment income	0		0
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	3		3
Other Income	2		2
Other, net	5		5
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	993		895
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	42		41
Decommissioning-Related Activities [Abstract]
Investment income	0		0
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	1		1
Other Income	1		2
Other, net	2		3
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	1,054		880
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	60		55
Decommissioning-Related Activities [Abstract]
Investment income	2	[4]	2	[4]
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	3		2
Other Income	(1)		1
Other, net	$ 4		$ 5

[1] For the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, utility taxes of $##D<gcytdutiltax> million and $##D<gpytdutiltax> million, respectively, are included in revenues and expenses for Generation. For the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, utility taxes of $##D<ccytdutiltax> million and $##D<cpytdutiltax> million, respectively, are included in revenues and expenses for ComEd. For the ##D<curmonth> months ended ##D<cyperiod> and ##D<pyfiscal>, utility taxes of $##D<pcytdutiltax> million and $##D<ppytdutiltax> million, respectively, are included in revenues and expenses for PECO. For the ##D<curmonth> months ended ##D<cyperiod> and period of March 12, 2012 through ##D<pyperiod>, utility taxes of $##D<bcytdutiltax> million and $##D<bpytdutiltax> 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] Relates to the cash return on BGE’s rate stabilization deferral. See Note 4 - Regulatory Matters for additional information regarding the rate stabilization deferral.