Supplemental Financial Information - Statement of Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Operating revenues [Abstract]
Total operating revenues	$ 6,284.00	$ 6,565.00	$ 5,954.00	$ 4,686.00	$ 4,357.00	$ 5,254.00	$ 4,496.00	$ 4,956.00	$ 23,489.00		$ 19,063.00		$ 18,644.00
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									463.00	[1]	443.00	[1]	476.00	[1]
Taxes other than income - real estate									227.00		177.00		175.00
Taxes other than income - payroll									131.00		123.00		121.00
Taxes other than income - other									198.00		42.00		36.00
Total taxes other than income									1,019.00		785.00		808.00
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments									(91.00)		(1.00)		0
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units									189.00	[2]	177.00	[2]	176.00	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units									102.00	[2]	45.00	[2]	51.00	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units									386.00		(74.00)		316.00
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement									105.00		(4.00)		104.00
Net unrealized income (losses) on pledged assets									73.00
Regulatory offset to decommissioning trust fund-related activities									(530.00)	[3]	130.00	[3]	(394.00)	[3]
Total decommissioning-related activities									325.00		62.00		253.00
Investment income									20.00		10.00		1.00
Long-term lease income									29.00		28.00		27.00
Interest income related to uncertain income tax positions									15.00		53.00		0
Income related to termination of a gas supply guarantee													0
Losses on early retirement of debt											36.00		0
Other-than-temporary impairment to Rabbi trust investments											0		0
Credit facility termination fees									85.00
AFUDC - equity									17.00		17.00		11.00
Realized gains on Rabbi Trust investments											0		1.00
Other									25.00		(3.00)		19.00
Other, net									346.00		203.00		312.00
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	3,928.00	4,017.00	3,753.00	2,739.00	2,528.00	2,821.00	2,455.00	2,643.00	14,437.00		10,447.00		10,025.00
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									82.00	[1]	27.00		0
Taxes other than income - real estate									189.00		146.00		142.00
Taxes other than income - payroll									78.00		71.00		70.00
Taxes other than income - other									20.00		20.00		18.00
Total taxes other than income									369.00		264.00		230.00
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments									(91.00)		(1.00)		0
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units									189.00	[2]	177.00	[2]	176.00	[2]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units									102.00	[2]	45.00	[2]	51.00	[2]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units									386.00		(74.00)		316.00
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement									105.00		(4.00)		104.00
Net unrealized income (losses) on pledged assets									73.00
Regulatory offset to decommissioning trust fund-related activities									(530.00)	[3]	130.00	[3]	(394.00)	[3]
Total decommissioning-related activities									325.00		62.00		253.00
Investment income									3.00
Interest income related to uncertain income tax positions									2.00		31.00		0
Income related to termination of a gas supply guarantee													0
Losses on early retirement of debt											36.00		0
Credit facility termination fees									85.00
Other									(6.00)		(8.00)		4.00
Other, net									239.00		122.00		257.00
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,290.00	1,484.00	1,281.00	1,388.00	1,362.00	1,784.00	1,444.00	1,466.00	5,443.00		6,056.00		6,204.00
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									239.00	[1]	243.00	[1]	205.00	[1]
Taxes other than income - real estate									22.00		22.00		20.00
Taxes other than income - payroll									26.00		25.00		24.00
Taxes other than income - other									8.00		6.00		7.00
Total taxes other than income									295.00		296.00		256.00
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									1.00		1.00		0
Interest income related to uncertain income tax positions									20.00		14.00		6.00
Other-than-temporary impairment to Rabbi trust investments											0		0
AFUDC - equity									6.00		8.00		4.00
Realized gains on Rabbi Trust investments											0		1.00
Other									12.00		6.00		13.00
Other, net									39.00		29.00		24.00
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	790.00	806.00	715.00	875.00	778.00	946.00	842.00	1,153.00	3,186.00		3,720.00		5,519.00
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									141.00	[1]	173.00	[1]	271.00	[1]
Taxes other than income - real estate									13.00		9.00		13.00
Taxes other than income - payroll									12.00		13.00		12.00
Taxes other than income - other									(4.00)		10.00		7.00
Total taxes other than income									162.00		205.00		303.00
Decommissioning-Related Activities [Abstract]
Investment income									2.00		3.00		1.00
Interest income related to uncertain income tax positions									0		1.00		0
AFUDC - equity									4.00		9.00		7.00
Other									2.00		1.00		0
Other, net									8.00		14.00		8.00
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	703.00	720.00	616.00	696.00	673.00	745.00	674.00	976.00	2,735.00		3,068.00		3,541.00
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility									75.00		79.00		79.00
Taxes other than income - real estate									111.00		107.00		102.00
Taxes other than income - payroll									18.00		17.00		16.00
Taxes other than income - other									4.00		4.00		3.00
Total taxes other than income									208.00		207.00		200.00
Decommissioning-Related Activities [Abstract]
Investment income									11.00		13.00		15.00
AFUDC - equity									10.00		15.00		10.00
Other									2.00		(2.00)
Other, net									$ 23.00		$ 26.00		$ 25.00

[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 13 - Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.