Segment Information - Generation Total Revenues (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 6,912	[1]	$ 6,502	[1]	$ 20,173	[2]	$ 18,725	[2]
Revenue from Related Parties	0	[3]	2	[3]	0	[4]	2	[4]
Net income (loss)	1,074		736		1,725		1,235
Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues							603
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,289		1,391		3,984	[5]	3,943	[5]
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	272		340		1,033		933
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	232		184		613	[5]	527	[5]
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	302		427		741		1,034
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	375	[6]	271	[6]	1,023	[6]	737	[6]
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,531		3,626		10,707		10,445
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	881	[7]	629	[7]	1,884	[8]	1,413	[8]
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,412	[9]	4,255	[9]	12,591		11,858
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	(15)
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,285	[9]	1,381	[9]	3,998	[10],[5]	3,932	[10],[5]
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	272	[9]	341	[9]	1,028	[10]	942	[10]
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	230	[9]	198	[9]	614	[10],[5]	547	[10],[5]
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	303	[9]	430	[9]	743	[10]	1,042	[10]
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	381	[6],[9]	278	[6],[9]	1,027	[10],[6]	708	[10],[6]
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,533	[9]	3,646	[9]	10,712	[10]	10,445	[10]
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues					12,591	[10]	11,858	[10]
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	4,412	[1],[11]	4,255	[1],[11]	12,591	[12],[2],[5]	11,858	[12],[2],[5]
Revenue from Related Parties	112	[11],[3]	373	[11],[3]	630	[12],[4],[5]	1,083	[12],[4],[5]
Net income (loss)	849	[11]	485	[11]	1,037	[12],[5]	795	[12],[5]
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	(417)	[1]	(668)	[1]	(1,573)	[2]	(2,003)	[2]
Revenue from Related Parties	(418)	[3]	(669)	[3]	(1,574)	[4]	(2,003)	[4]
Net income (loss)	0		0		0		0
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	4		10		(14)	[5]	11	[5]
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	0		(1)		5		(9)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	2		(14)		(1)	[5]	(20)	[5]
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	(1)		(3)		(2)		(8)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	(6)	[6]	(7)	[6]	(4)	[6]	29	[6]
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	(2)		(20)		(5)		0
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	2	[7]	20	[7]	5	[8]	0	[8]
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	0		0		0		0
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	305	[1],[13]	294	[1],[13]	924	[13],[2]	909	[13],[2]
Revenue from Related Parties	302	[13],[3]	294	[13],[3]	920	[13],[4]	909	[13],[4]
Net income (loss)	(31)	[13]	(20)	[13]	(58)	[13]	(152)	[13]
Other Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	879	[7],[9]	609	[7],[9]	1,879	[10],[8]	1,413	[10],[8]
Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	22		125		203
Commonwealth Edison Co Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	$ 1		$ 143		$ 175		$ 409

[1] For the three months ended September 30, 2014 and 2013, utility taxes of $22 million and $21 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2014 and 2013, utility taxes of $61 million and $65 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2014 and 2013, utility taxes of $34 million and $33 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2014 and 2013, utility taxes of $21 million and $20 million, respectively, are included in revenues and expenses for BGE.

[2] For the nine months ended September 30, 2014 and 2013, utility taxes of $67 million and $60 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2014 and 2013, utility taxes of $180 million and $182 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2014 and 2013, utility taxes of $99 million and $97 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2014 and 2013, utility taxes of $64 million and $62 million, respectively, are included in revenues and expenses for BGE.

[3] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

[4] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with the Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

[5] Amounts include activity recorded at CENG from April 1, 2014, the date of integration, through September 30, 2014.

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

[7] 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 date of merger with Constellation and the consolidation of CENG in purchase accounting of $22 million decrease to revenues and $125 million decrease to revenues for the three months ended September 30, 2014 and 2013, respectively, and the elimination of intersegment revenues.

[8] 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 date of merger with Constellation and the consolidation of CENG in purchase accounting of $203 million decrease to revenues and $603 million decrease to revenues, for the nine months ended September 30, 2014 and 2013, respectively, and elimination of intersegment revenues.

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

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

[11] 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, 2014 include revenue from sales to PECO of $28 million and sales to BGE of $83 million in the Mid-Atlantic region, and sales to ComEd of $1 million in the Midwest region. For the three months ended September 30, 2013, intersegment revenues for Generation include revenue from sales to PECO of $82 million and sales to BGE of $144 million in the Mid-Atlantic region, and sales to ComEd of $143 million in the Midwest region

[12] 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, 2014 include revenue from sales to PECO of $165 million and sales to BGE of $290 million in the Mid-Atlantic region, and sales to ComEd of $175 million in the Midwest. For the nine months ended September 30, 2013, intersegment revenues for Generation include revenue from sales to PECO of $321 million and sales to BGE of $356 million in the Mid-Atlantic region, and sales to ComEd of $409 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.

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