Segment Information (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended				9 Months Ended						3 Months Ended				9 Months Ended					3 Months Ended				9 Months Ended						3 Months Ended				9 Months Ended						3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended					3 Months Ended				9 Months Ended					3 Months Ended		7 Months Ended		9 Months Ended
	Sep. 30, 2012 ReportableSegments	Sep. 30, 2011	Sep. 30, 2012 ReportableSegments	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 All Other Segments [Member]		Sep. 30, 2011 All Other Segments [Member]		Sep. 30, 2012 All Other Segments [Member]		Sep. 30, 2011 All Other Segments [Member]		Dec. 31, 2011 All Other Segments [Member]		Sep. 30, 2012 Business Intersegment Eliminations [Member]		Sep. 30, 2011 Business Intersegment Eliminations [Member]		Sep. 30, 2012 Business Intersegment Eliminations [Member]		Sep. 30, 2011 Business Intersegment Eliminations [Member]		Dec. 31, 2011 Business Intersegment Eliminations [Member]	Sep. 30, 2012 Reportable Segment [Member]		Sep. 30, 2011 Reportable Segment [Member]		Sep. 30, 2012 Reportable Segment [Member]		Sep. 30, 2011 Reportable Segment [Member]		Dec. 31, 2011 Reportable Segment [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] ReportableSegments	Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member]		Sep. 30, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member]		Sep. 30, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member] Baltimore Gas And Electric Company Affiliate [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member] Baltimore Gas And Electric Company Affiliate [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member] Commonwealth Edison Co Affiliate [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member] Commonwealth Edison Co Affiliate [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member] Commonwealth Edison Co Affiliate [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member] Commonwealth Edison Co Affiliate [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member] PECO Energy Co Affiliate [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member] PECO Energy Co Affiliate [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Reportable Segment [Member] PECO Energy Co Affiliate [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member] Reportable Segment [Member] PECO Energy Co Affiliate [Member]	Sep. 30, 2012 Generation Mid Atlantic [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Mid Atlantic [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Mid Atlantic [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Mid Atlantic [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Midwest [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Midwest [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Midwest [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Midwest [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation New England [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation New England [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation New England [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation New England [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation New York [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation New York [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation New York [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation New York [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation ERCOT [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation ERCOT [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation ERCOT [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation ERCOT [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Other Regions [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Other Regions [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Other Regions [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Other Regions [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Reportable Segments Total [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Reportable Segments Total [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Reportable Segments Total [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Reportable Segments Total [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Total Consolidated Group [Member] All Other Segments [Member]		Sep. 30, 2011 Generation Total Consolidated Group [Member] All Other Segments [Member]		Sep. 30, 2012 Generation Total Consolidated Group [Member] All Other Segments [Member]		Sep. 30, 2011 Generation Total Consolidated Group [Member] All Other Segments [Member]		Sep. 30, 2012 Generation Total Consolidated Group [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Total Consolidated Group [Member] Reportable Segment [Member]		Sep. 30, 2012 Generation Total Consolidated Group [Member] Reportable Segment [Member]		Sep. 30, 2011 Generation Total Consolidated Group [Member] Reportable Segment [Member]		Sep. 30, 2012 Commonwealth Edison Co [Member] Reportable Segment [Member]		Sep. 30, 2011 Commonwealth Edison Co [Member] Reportable Segment [Member]		Sep. 30, 2012 Commonwealth Edison Co [Member] Reportable Segment [Member]		Sep. 30, 2011 Commonwealth Edison Co [Member] Reportable Segment [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member] Reportable Segment [Member]	Sep. 30, 2012 PECO Energy Co [Member] Reportable Segment [Member]		Sep. 30, 2011 PECO Energy Co [Member] Reportable Segment [Member]		Sep. 30, 2012 PECO Energy Co [Member] Reportable Segment [Member]		Sep. 30, 2011 PECO Energy Co [Member] Reportable Segment [Member]		Dec. 31, 2011 PECO Energy Co [Member] Reportable Segment [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Reportable Segment [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Reportable Segment [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member] Reportable Segment [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers																																																							$ 1,428,000,000	[1]	$ 1,032,000,000	[1]	$ 3,832,000,000	[1]	$ 3,102,000,000	[1]	$ 1,193,000,000	[1]	$ 1,385,000,000	[1]	$ 3,600,000,000	[1]	$ 4,151,000,000	[1]	$ 390,000,000	[1]	$ 2,000,000	[1]	$ 776,000,000	[1]	$ 8,000,000	[1]	$ 183,000,000	[1]	$ 0	[1]	$ 394,000,000	[1]	$ 0	[1]	$ 532,000,000	[1]	$ 307,000,000	[1]	$ 1,073,000,000	[1]	$ 507,000,000	[1]	$ 317,000,000	[1],[2]	$ 77,000,000	[1],[2]	$ 611,000,000	[1],[3]	$ 169,000,000	[1],[3]	$ 4,043,000,000	[1]	$ 2,803,000,000	[1]	$ 10,286,000,000	[1]	$ 7,937,000,000	[1]	$ (35,000,000)	[1],[4]	$ 18,000,000	[1],[4]	$ 212,000,000	[1],[4]	$ (18,000,000)	[1],[4]	$ 4,008,000,000	[1]	$ 2,821,000,000	[1]	$ 10,498,000,000	[1]	$ 7,919,000,000	[1]
Intersegment revenues						334,000,000	[5],[6]	203,000,000	[5],[6]	1,050,000,000	[5],[7]	576,000,000	[5],[7]			(798,000,000)	[5]	(503,000,000)	[5]	(2,291,000,000)	[5]	(1,429,000,000)	[5]		0	[5]	7,000,000	[5]	4,000,000	[5]	9,000,000	[5]			459,000,000	[5],[8]	304,000,000	[5],[8]	1,233,000,000	[5],[9]	856,000,000	[5],[9]			120,000,000	223,000,000	180,000,000	159,000,000	631,000,000	450,000,000	171,000,000	137,000,000	407,000,000	394,000,000	(11,000,000)				(43,000,000)				7,000,000				19,000,000				1,000,000				36,000,000				2,000,000				(22,000,000)				1,000,000				1,000,000				12,000,000	[2]			40,000,000	[3]			12,000,000				31,000,000				(3,000,000)	[4]			(20,000,000)	[4]			9,000,000				11,000,000				0	[5]	1,000,000	[5]	2,000,000	[5]	2,000,000	[5]		1,000,000	[5]	2,000,000	[5]	3,000,000	[5]	4,000,000	[5]		4,000,000	[5]	7,000,000	[10],[5]
Revenues	6,565,000,000	5,254,000,000	17,205,000,000	14,705,000,000		336,000,000	[6]	206,000,000	[6]	1,049,000,000	[7]	579,000,000	[7]			(798,000,000)		(503,000,000)		(2,291,000,000)		(1,429,000,000)			6,565,000,000	[11]	5,254,000,000	[11]	17,205,000,000	[12]	14,705,000,000	[12]			4,017,000,000	[11],[8]	2,821,000,000	[11],[8]	10,509,000,000	[12],[9]	7,919,000,000	[12],[9]													1,417,000,000		1,032,000,000		3,789,000,000		3,102,000,000		1,200,000,000		1,385,000,000		3,619,000,000		4,151,000,000		391,000,000		2,000,000		812,000,000		8,000,000		185,000,000		0		372,000,000		0		533,000,000		307,000,000		1,074,000,000		507,000,000		329,000,000	[2]	77,000,000	[2]	651,000,000	[3]	169,000,000	[3]	4,055,000,000		2,803,000,000		10,317,000,000		7,937,000,000		(38,000,000)	[4]	18,000,000	[4]	192,000,000	[4]	(18,000,000)	[4]	4,017,000,000		2,821,000,000		10,509,000,000		7,919,000,000		1,484,000,000	[11]	1,784,000,000	[11]	4,154,000,000	[12]	4,694,000,000	[12]		806,000,000	[11]	946,000,000	[11]	2,396,000,000	[12]	2,942,000,000	[12]		720,000,000	[11]	1,388,000,000	[10],[12]
Revenue net of purchased power and fuel expense from external customers																																																							919,000,000	[13]	835,000,000		2,605,000,000	[14]	2,567,000,000	[14]	723,000,000	[13]	852,000,000		2,291,000,000	[14]	2,704,000,000	[14]	80,000,000	[13]	1,000,000		144,000,000	[14]	6,000,000	[14]	11,000,000	[13]	0		82,000,000	[14]	0	[14]	158,000,000	[13]	103,000,000		311,000,000	[14]	94,000,000	[14]	30,000,000	[13],[2]	(4,000,000)	[2]	49,000,000	[14],[2]	(10,000,000)	[14],[2]	1,921,000,000	[13]	1,787,000,000		5,482,000,000	[14]	5,361,000,000	[14]	(26,000,000)	[13],[4]	(37,000,000)	[4]	9,000,000	[14],[4]	(237,000,000)	[14],[4]	1,895,000,000	[13]	1,750,000,000		5,491,000,000	[14]	5,124,000,000	[14]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity																																																							(11,000,000)				(44,000,000)				7,000,000				19,000,000				1,000,000				36,000,000				2,000,000				(22,000,000)				0				1,000,000				12,000,000	[2]			41,000,000	[2]			11,000,000				31,000,000				(11,000,000)	[4]			(31,000,000)	[4]			0				0
Revenue net of purchased power and fuel expense, Total																																																							908,000,000		835,000,000		2,561,000,000		2,567,000,000		730,000,000		852,000,000		2,310,000,000		2,704,000,000		81,000,000		1,000,000		180,000,000		6,000,000		13,000,000		0		60,000,000		0		158,000,000		103,000,000		312,000,000		94,000,000		42,000,000	[2]	(4,000,000)	[2]	90,000,000	[2]	(10,000,000)	[2]	1,932,000,000		1,787,000,000		5,513,000,000		5,361,000,000		(37,000,000)	[4]	(37,000,000)	[4]	(22,000,000)	[4]	(237,000,000)	[4]	1,895,000,000		1,750,000,000		5,491,000,000		5,124,000,000
Income taxes	161,000,000	255,000,000	445,000,000	1,034,000,000
Net income (loss)						(3,000,000)	[6]	(1,000,000)	[6]	(101,000,000)	[7]	(45,000,000)	[7]			0		0		0		0			297,000,000		602,000,000		787,000,000		1,889,000,000				87,000,000	[8]	386,000,000	[8]	419,000,000	[9]	1,325,000,000	[9]																																																																																					90,000,000		112,000,000		219,000,000		295,000,000			123,000,000		105,000,000		300,000,000		314,000,000			0		(50,000,000)	[10]
Total assets	78,353,000,000		78,353,000,000		54,995,000,000	10,150,000,000	[6]			10,150,000,000	[6]			6,162,000,000	[6]	(12,523,000,000)				(12,523,000,000)				(10,394,000,000)	78,353,000,000				78,353,000,000				54,995,000,000		41,090,000,000	[8]			41,090,000,000	[8]			27,433,000,000	[8]																																																																																			22,471,000,000				22,471,000,000				22,638,000,000	9,661,000,000				9,661,000,000				9,156,000,000	7,504,000,000		7,504,000,000		7,504,000,000
Segment Reporting Additional Information [Abstract]
Number of reportable segments	9		9																															6
Utility taxes																																			28,000,000		7,000,000		60,000,000		20,000,000																																																																																						67,000,000		64,000,000		182,000,000		184,000,000			40,000,000		50,000,000		108,000,000		140,000,000			20,000,000				42,000,000
Unrealized Gain (Loss) on Derivatives			$ 377,000,000	$ (360,000,000)																																											$ (15,000,000)		$ 30,000,000

[1] Includes all wholesale and retail electric sales from third parties and affiliated sales to ComEd, PECO and BGE.

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

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

[4] Other represents activities not allocated to a region and includes retail and wholesale gas, upstream natural gas, proprietary trading, demand response, energy efficiency, the design, construction, and operation of renewable energy, heating, cooling, and cogeneration facilities, home improvements, sales of electric and gas appliances, servicing of heating, air conditioning, plumbing, electrical, and indoor quality systems, mark-to-market activities associated with Generation's economic hedging activities. In addition, includes generation under the reliability-must-run rate schedule and generation of Brandon Shores, H.A. Wagner, and C.P. Crane, the generating facilities planned for divestiture as a result of the Exelon and Constellation merger. Also includes amortization of intangible assets related to commodity contracts recorded at fair value at the merger date.

[5] 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 2 of the Exelon 2011 Form 10-K for additional information on AECs. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations.

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

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

[8] 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 three months ended September 30, 2012 include revenue from sales to PECO of $ 171 million and sales to BGE of $120 million in the Mid-Atlantic region, and sales to ComEd of $180 million in the Midwest region, net of $ (15) million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. For the three months ended September 30, 2011 intersegment revenues for Generation include revenue from sales to PECO of $137 million in the Mid-Atlantic region, and sales to ComEd of $159 million in the Midwest region.

[9] 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 nine months ended September 30, 2012 include revenue from sales to PECO of $407 million and sales to BGE of $223 million in the Mid-Atlantic region, and sales to ComEd of $631 million in the Midwest region, net of $ (30) million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. For the nine months ended September 30, 2011 intersegment revenues for Generation include revenue from sales to PECO of $394 million in the Mid-Atlantic region, and sales to ComEd of $450 million in the Midwest region.

[10] Amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through September 30, 2012.

[11] For the three months ended September 30, 2012 and 2011, utility taxes of $28 million and $7 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2012 and 2011, utility taxes of $67 million and $64 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2012 and 2011, utility taxes of $40 million and $50 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2012, utility taxes of $20 million are included in revenues and expenses for BGE.

[12] For the nine months ended September 30, 2012 and 2011, utility taxes of $ 60 million and $ 20 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2012 and 2011, utility taxes of $182 million and $184 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2012 and 2011, utility taxes of $108 million and $140 million, respectively, are included in revenues and expenses for PECO. For the period of March 12, 2012 through September 30, 2012, utility taxes of $42 million are included in revenues and expenses for BGE.

[13] Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE.

[14] Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE.