Segment Information (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
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											$ 23,489.00	[1]	$ 19,063.00	[1]	$ 18,644.00	[1]
Intersegment revenues											55.00	[2]	9.00	[2]	6.00	[2]
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
Income (loss) from continuing operations before income taxes											1,798.00		3,956.00		4,221.00
Depreciation and amortization											1,881.00		1,347.00		2,075.00
Operating Expenses											21,018.00	[1]	14,583.00	[1]	13,918.00	[1]
Interest Revenue (Expense), Net											928.00		726.00		817.00
Income taxes											627.00		1,457.00		1,658.00
Net income (loss)											1,171.00		2,499.00		2,563.00
Equity in earnings (losses) of unconsolidated affiliates											(91.00)		(1.00)
Capital expenditures											5,789.00		4,042.00		3,326.00
Total assets	78,554.00					54,995.00					78,554.00		54,995.00
Segment Reporting Additional Information [Abstract]
Utility taxes											463.00	[3]	443.00	[3]	476.00	[3]
Unrealized Gain (Loss) on Derivatives											604.00		(291.00)		88.00
All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											1,396.00	[1],[4]	830.00	[1],[4]	755.00	[1],[4]
Intersegment revenues											1,381.00	[4]	831.00	[4]	756.00	[4]
Income (loss) from continuing operations before income taxes											(276.00)	[4]	(59.00)	[4]	(91.00)	[4]
Depreciation and amortization											46.00	[4]	21.00	[4]	25.00	[4]
Operating Expenses											1,662.00	[1],[4]	863.00	[1],[4]	792.00	[1],[4]
Interest Revenue (Expense), Net											86.00	[4]	77.00	[4]	85.00	[4]
Income taxes											(215.00)	[4]	9.00	[4]	(27.00)	[4]
Net income (loss)											(61.00)	[4]	(68.00)	[4]	(64.00)	[4]
Capital expenditures											67.00	[4]	42.00	[4]	14.00	[4]
Total assets	10,432.00	[4]				6,147.00	[4]				10,432.00	[4]	6,147.00	[4]
Business Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											(3,064.00)	[1]	(1,990.00)	[1]	(3,859.00)	[1]
Intersegment revenues											(3,042.00)	[2]	(1,990.00)	[2]	(3,859.00)	[2]
Income (loss) from continuing operations before income taxes											(56.00)		(13.00)		(8.00)
Depreciation and amortization											2.00
Operating Expenses											(3,043.00)	[1]	(1,990.00)	[1]	(3,859.00)	[1]
Income taxes											(1.00)		(4.00)		(2.00)
Net income (loss)											(55.00)		(9.00)		(6.00)
Capital expenditures															(78.00)	[5]
Total assets	(12,316.00)					(10,379.00)					(12,316.00)		(10,379.00)
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											14,437.00	[1],[6]	10,447.00	[1],[6]	10,025.00	[1],[6]
Intersegment revenues											1,702.00	[2],[6]	1,161.00	[2],[6]	3,102.00	[2],[6]
Income (loss) from continuing operations before income taxes											1,058.00	[6]	2,827.00	[6]	3,150.00	[6]
Depreciation and amortization											768.00	[6]	570.00	[6]	474.00	[6]
Operating Expenses											13,226.00	[1],[6]	7,571.00	[1],[6]	6,979.00	[1],[6]
Interest Revenue (Expense), Net											301.00	[6]	170.00	[6]	153.00	[6]
Income taxes											500.00	[6]	1,056.00	[6]	1,178.00	[6]
Net income (loss)											558.00	[6]	1,771.00	[6]	1,972.00	[6]
Equity in earnings (losses) of unconsolidated affiliates											(91.00)	[6]	(1.00)	[6]
Capital expenditures											3,554.00	[6]	2,491.00	[6]	1,883.00	[6]
Total assets	40,681.00	[6]				27,433.00	[6]				40,681.00	[6]	27,433.00	[6]
Segment Reporting Additional Information [Abstract]
Utility taxes											82.00		27.00		0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											5,038.00		4,052.00		3,232.00
Intersegment revenues											(44.00)
Revenues											5,082.00	[7]	4,052.00	[7]	3,232.00	[7]
Revenue net of purchased power and fuel expense from external customers											3,477.00		3,350.00		2,501.00
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											(44.00)
Revenue net of purchased power and fuel expense, Total											3,433.00		3,350.00		2,501.00
Generation Mid Atlantic [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues											322.00
Generation Mid Atlantic [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues											543.00		508.00		2,092.00
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											4,848.00		5,445.00		5,762.00
Intersegment revenues											24.00
Revenues											4,824.00	[7]	5,445.00	[7]	5,762.00	[7]
Revenue net of purchased power and fuel expense from external customers											2,974.00		3,547.00		4,081.00
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											24.00
Revenue net of purchased power and fuel expense, Total											2,998.00		3,547.00		4,081.00
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Intersegment revenues											795.00		653.00		1,010.00
Segment Reporting Additional Information [Abstract]
Unrealized Gain (Loss) on Derivatives											7.00
Generation New England [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											1,093.00		11.00		14.00
Intersegment revenues											45.00
Revenues											1,048.00	[7]	11.00	[7]	14.00	[7]
Revenue net of purchased power and fuel expense from external customers											151.00		9.00		11.00
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											45.00
Revenue net of purchased power and fuel expense, Total											196.00		9.00		11.00
Generation New York [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											557.00
Intersegment revenues											(25.00)
Revenues											582.00	[7]
Revenue net of purchased power and fuel expense from external customers											101.00
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											(25.00)
Revenue net of purchased power and fuel expense, Total											76.00
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											1,367.00		575.00		543.00
Intersegment revenues											2.00
Revenues											1,365.00	[7]	575.00	[7]	543.00	[7]
Revenue net of purchased power and fuel expense from external customers											403.00		84.00		(66.00)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											2.00
Revenue net of purchased power and fuel expense, Total											405.00		84.00		(66.00)
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											833.00	[8]	201.00	[8]	149.00	[8]
Intersegment revenues											78.00	[8]
Revenues											755.00	[7],[8]	201.00	[7],[8]	149.00	[7],[8]
Revenue net of purchased power and fuel expense from external customers											53.00	[8]	(14.00)	[8]	(65.00)	[8]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											78.00	[8]
Revenue net of purchased power and fuel expense, Total											131.00	[8]	(14.00)	[8]	(65.00)	[8]
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											13,736.00		10,284.00		9,700.00
Intersegment revenues											80.00
Revenues											13,656.00	[7]	10,284.00	[7]	9,700.00	[7]
Revenue net of purchased power and fuel expense from external customers											7,159.00		6,976.00		6,462.00
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											80.00
Revenue net of purchased power and fuel expense, Total											7,239.00		6,976.00		6,462.00
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											14,437.00		10,447.00		10,025.00
Intersegment revenues											0
Revenues											14,437.00	[7]	10,447.00	[7]	10,025.00	[7]
Revenue net of purchased power and fuel expense from external customers											7,376.00		6,858.00		6,562.00
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											0
Revenue net of purchased power and fuel expense, Total											7,376.00		6,858.00		6,562.00
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											701.00	[9]	163.00	[9]	325.00	[9]
Intersegment revenues											(80.00)	[9]
Revenues											781.00	[9]	163.00	[9]	325.00	[9]
Revenue net of purchased power and fuel expense from external customers											217.00	[9]	(118.00)	[9]	100.00	[9]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity											(80.00)	[9]
Revenue net of purchased power and fuel expense, Total											137.00	[9]	(118.00)	[9]	100.00	[9]
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											5,443.00	[1]	6,056.00	[1]	6,204.00	[1]
Intersegment revenues											2.00		2.00		2.00
Income (loss) from continuing operations before income taxes											618.00		666.00		694.00
Depreciation and amortization											610.00		554.00		516.00
Operating Expenses											4,557.00	[1]	5,074.00	[1]	5,148.00	[1]
Interest Revenue (Expense), Net											307.00		345.00		386.00
Income taxes											239.00		250.00		357.00
Net income (loss)											379.00		416.00		337.00
Capital expenditures											1,246.00		1,028.00		962.00
Total assets	22,905.00					22,638.00					22,905.00		22,638.00
Segment Reporting Additional Information [Abstract]
Utility taxes													243.00		205.00
Commonwealth Edison Co [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Additional Information [Abstract]
Utility taxes											239.00
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											3,186.00	[1]	3,720.00	[1]	5,519.00	[1]
Intersegment revenues											3.00	[2]	5.00	[2]	5.00	[2]
Income (loss) from continuing operations before income taxes											508.00		535.00		476.00
Depreciation and amortization											217.00		202.00		1,060.00
Operating Expenses											2,563.00	[1]	3,065.00	[1]	4,858.00	[1]
Interest Revenue (Expense), Net											123.00		134.00		193.00
Income taxes											127.00		146.00		152.00
Net income (loss)											381.00		389.00		324.00
Capital expenditures											422.00		481.00		545.00
Total assets	9,353.00					9,156.00					9,353.00		9,156.00
Segment Reporting Additional Information [Abstract]
Utility taxes											141.00		173.00		271.00
Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Revenue for Reportable Segment											2,091.00	[1],[10]
Intersegment revenues											9.00	[10]
Income (loss) from continuing operations before income taxes											(54.00)	[10]
Depreciation and amortization											238.00	[10]
Operating Expenses											2,053.00	[1],[10]
Interest Revenue (Expense), Net											111.00	[10]
Income taxes											(23.00)	[10]
Net income (loss)											(31.00)	[10]
Capital expenditures											500.00	[10]
Total assets	7,499.00	[10]									7,499.00	[10]
Segment Reporting Additional Information [Abstract]
Utility taxes											$ 59.00

[1] For the years ended December 31, 2012, 2011 and 2010, utility taxes of $82 million, $27 million and $0 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2012, 2011 and 2010, utility taxes of $239 million, $243 million and $205 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2012, 2011 and 2010, utility taxes of $141 million, $173 million and $271 million, respectively, are included in revenues and expenses for PECO. For the period of March 12, 2012 through December 31, 2012, utility taxes of $59 million are included in revenues and expenses for BGE.

[2] The intersegment profit associated with Generation's sale of AECs to PECO is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. See Note 3 for additional information on AECs. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations.

[3] 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.

[4] Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.

[5] Represents capital projects transferred from BSC to Generation, ComEd and PECO. These projects are shown as capital expenditures at Generation, ComEd and PECO and the capital expenditure is eliminated upon consolidation.

[6] Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Regions. Intersegment revenues for Generation for the year ended December 31, 2012 include revenue from sales to PECO of $543 million and sales to BGE of $322 million in the Mid-Atlantic region, and sales to ComEd of $795 million in the Midwest region, net of $7 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. For the years ended December 31, 2011 and 2010 intersegment revenues for Generation include revenue from sales to PECO of $508 million and $2,092 million, respectively, in the Mid-Atlantic region, and sales to ComEd of $653 million and $1,010 million, respectively, in the Midwest region.

[7] Includes all electric sales to third parties and affiliated sales to ComEd, PECO and BGE.

[8] Other regions include the South, West and Canada, which are not considered individually significant.

[9] Other represents activities not allocated to a region. See text above for a description of included activities. Also includes amortization of intangible assets related to commodity contracts recorded at fair value at the merger date.

[10] Amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through December 31, 2012.