Segment Information - Reconciliation to Consolidated Financial Statements (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		Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 6,912	[1]	$ 6,502	[1]	$ 20,173	[2]	$ 18,725	[2]
Operating revenues from affiliates	0	[3]	2	[3]	0	[4]	2	[4]
Net income (loss)	1,074		736		1,725		1,235
Assets	85,264		79,924		85,264		79,924		79,924
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	(15)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,061		1,013		3,313		3,271
Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues							603
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,412	[5]	4,255	[5]	12,591		11,858
Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	22		125		203
Operating Segments [Member]
Segment Reporting Information [Line Items]
Utility taxes	22		21		67		60
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	4,412	[1],[6]	4,255	[1],[6]	12,591	[2],[7],[8]	11,858	[2],[7],[8]
Operating revenues from affiliates	112	[3],[6]	373	[3],[6]	630	[4],[7],[8]	1,083	[4],[7],[8]
Net income (loss)	849	[6]	485	[6]	1,037	[7],[8]	795	[7],[8]
Assets	45,019	[6]	41,232	[6]	45,019	[6]	41,232	[6]
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,062	[5]	1,018	[5]	3,302	[9]	3,274	[9]
Operating Segments [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Revenues	1,222	[1]	1,156	[1]	3,484	[2]	3,395	[2]
Operating revenues from affiliates	1	[3]	1	[3]	2	[4]	2	[4]
Net income (loss)	126		126		335		140
Assets	24,845		24,118		24,845		24,118
Utility taxes	61		65		180		182
Operating Segments [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues	693	[1]	728	[1]	2,343	[2]	2,295	[2]
Operating revenues from affiliates	0	[3]	1	[3]	1	[4]	1	[4]
Net income (loss)	81		92		255		292
Assets	10,051		9,617		10,051		9,617
Utility taxes	34		33		99		97
Operating Segments [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Revenues	697	[1]	737	[1]	2,404	[2]	2,271	[2]
Operating revenues from affiliates	3	[3]	2	[3]	21	[4]	10	[4]
Net income (loss)	49		53		156		160
Assets	7,915		7,861		7,915		7,861
Utility taxes	21		20		64		62
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues					12,591	[9]	11,858	[9]
Operating Segments [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	28		82		165		321
Operating Segments [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	83		144		290		356
Operating Segments [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues	1		143		175		409
Operating Segments [Member] | Commonwealth Edison Co Affiliate [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues							7
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	305	[1],[10]	294	[1],[10]	924	[10],[2]	909	[10],[2]
Operating revenues from affiliates	302	[10],[3]	294	[10],[3]	920	[10],[4]	909	[10],[4]
Net income (loss)	(31)	[10]	(20)	[10]	(58)	[10]	(152)	[10]
Assets	8,713	[10]	8,317	[10]	8,713	[10]	8,317	[10]
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	(1)		(5)		11		(3)
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	(417)	[1]	(668)	[1]	(1,573)	[2]	(2,003)	[2]
Operating revenues from affiliates	(418)	[3]	(669)	[3]	(1,574)	[4]	(2,003)	[4]
Net income (loss)	0		0		0		0
Assets	(11,279)		(11,221)		(11,279)		(11,221)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	$ 0		$ 0		$ 0		$ 0

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

[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 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

[7] 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.

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

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

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