Segment Information - Analysis and Reconciliation to Consolidated Financial Statements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended											10 Months Ended		12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013		Dec. 31, 2012		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 7,255		$ 6,912	$ 6,024	$ 7,237	$ 6,163		$ 6,502	$ 6,141	$ 6,082				$ 27,429	[1]	$ 24,888	[1]	$ 23,489	[1]
Operating revenues from affiliates														23		70		48
Depreciation and amortization														2,314		2,153		1,881
Operating Expenses														25,039	[1]	21,242	[1]	21,018	[1]
Equity in earnings (losses) of unconsolidated affiliates														(20)		10		(91)
Interest expense, net														1,065		1,356		928
Income (loss) from continuing operations before income taxes														2,486		2,773		1,798
Income taxes														666		1,044		627
Net income	18	[2]	993	522	90	495		738	490	(4)	[3]			1,820		1,729		1,171
Capital expenditures														6,077		5,395		5,789
Assets	86,814	[4]				79,924	[4]							86,814	[4]	79,924	[4]
Utility taxes														456	[5]	449	[5]	463	[5]
PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														1	[6]	10	[6]	6	[6]
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues														4,475		4,270		4,848
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues														17,393	[1],[7]	15,630	[1],[7]	14,437	[1],[7]
Depreciation and amortization														967	[7]	856	[7]	768	[7]
Operating Expenses														16,923	[1],[7]	13,976	[1],[7]	13,226	[1],[7]
Equity in earnings (losses) of unconsolidated affiliates														(20)	[7]	10	[7]	(91)	[7]
Interest expense, net														356	[7]	357	[7]	301	[7]
Income (loss) from continuing operations before income taxes														1,226	[7]	1,675	[7]	1,058	[7]
Income taxes														207	[7]	615	[7]	500	[7]
Net income														1,019	[7]	1,060	[7]	558	[7]
Capital expenditures														3,012	[7]	2,752	[7]	3,554	[7]
Assets	45,348	[7]				41,232	[7]							45,348	[7]	41,232	[7]
Operating Segments [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Revenues														4,564	[1]	4,464	[1]	5,443	[1]
Depreciation and amortization														687		669		610
Operating Expenses														3,586	[1]	3,510	[1]	4,557	[1]
Equity in earnings (losses) of unconsolidated affiliates														0		0		0
Interest expense, net														321		579		307
Income (loss) from continuing operations before income taxes														676		401		618
Income taxes														268		152		239
Net income														408		249		379
Capital expenditures														1,689		1,433		1,246
Assets	25,392					24,118								25,392		24,118
Operating Segments [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues														3,094	[1]	3,100	[1]	3,186	[1]
Depreciation and amortization														236		228		217
Operating Expenses														2,522	[1]	2,434	[1]	2,563	[1]
Equity in earnings (losses) of unconsolidated affiliates														0		0		0
Interest expense, net														113		115		123
Income (loss) from continuing operations before income taxes														466		557		508
Income taxes														114		162		127
Net income														352		395		381
Capital expenditures														661		537		422
Assets	9,943					9,617								9,943		9,617
Operating Segments [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Revenues														3,165	[1],[8]	3,065	[1],[8]	2,091	[1],[8]
Depreciation and amortization														371	[8]	348	[8]	238	[8]
Operating Expenses														2,726	[1],[8]	2,616	[1],[8]	2,053	[1],[8]
Equity in earnings (losses) of unconsolidated affiliates														0	[8]	0	[8]	0	[8]
Interest expense, net														106	[8]	122	[8]	111	[8]
Income (loss) from continuing operations before income taxes														351	[8]	344	[8]	(54)	[8]
Income taxes														140	[8]	134	[8]	(23)	[8]
Net income														211	[8]	210	[8]	(31)	[8]
Capital expenditures														620	[8]	587	[8]	500	[8]
Assets	8,078	[8]				7,861	[8]							8,078	[8]	7,861	[8]
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues														4,467	[9]	4,280	[9]	4,824	[9]
Income (loss) from continuing operations before income taxes																7
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues														1,285	[1],[10]	1,241	[1],[10]	1,396	[1],[10]
Depreciation and amortization														53	[10]	52	[10]	48	[10]
Operating Expenses														1,353	[1],[10]	1,324	[1],[10]	1,662	[1],[10]
Equity in earnings (losses) of unconsolidated affiliates														0	[10]	0	[10]	0	[10]
Interest expense, net														169	[10]	183	[10]	86	[10]
Income (loss) from continuing operations before income taxes														(227)	[10]	(191)	[10]	(325)	[10]
Income taxes														(63)	[10]	(20)	[10]	(215)	[10]
Net income														(164)	[10]	(171)	[10]	(110)	[10]
Capital expenditures														95	[10]	86	[10]	67	[10]
Assets	9,794	[10]				8,317	[10]							9,794	[10]	8,317	[10]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues														(2,072)	[1]	(2,612)	[1]	(3,064)	[1]
Operating revenues from affiliates														6	[11]	14	[11]	6	[11]
Depreciation and amortization														0		0		0
Operating Expenses														(2,071)	[1]	(2,618)	[1]	(3,043)	[1]
Equity in earnings (losses) of unconsolidated affiliates														0		0		0
Interest expense, net														0		0		0
Income (loss) from continuing operations before income taxes														(6)		(13)		(7)
Income taxes														0		1		(1)
Net income														(6)		(14)		(6)
Capital expenditures														0		0		0
Assets	(11,741)					(11,221)								(11,741)		(11,221)
Intersegment Eliminations [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														762	[11],[7]	1,367	[11],[7]	1,660	[11],[7]
Intersegment Eliminations [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														4	[11]	3	[11]	2	[11]
Intersegment Eliminations [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														2	[11]	1	[11]	3	[11]
Intersegment Eliminations [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														25	[11],[8]	13	[11],[8]	9	[11],[8]
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														1,280	[10],[11]	1,237	[10],[11]	1,381	[10],[11]
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														8		(10)		24
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates														(2,067)	[11]	(2,607)	[11]	(3,049)	[11]
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	4,802		4,412	3,789	4,390	3,772		4,255	4,070	3,533				17,393		15,630		14,437
Operating revenues from affiliates														779		1,423		1,702
Income (loss) from continuing operations before income taxes														1,226		1,675		1,058
Income taxes														207		615		500
Net income	(91)		771	340	(185)	269		490	330	(18)				1,019		1,060		558
Assets	45,348	[12]				41,232	[12]							45,348	[12]	41,232	[12]
Utility taxes														89	[5]	79	[5]	82	[5]
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues														198	[13]
Operating revenues from affiliates																405	[13]	543	[13]
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues														387	[14]
Operating revenues from affiliates																455	[14]	322	[14]
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Revenues														176	[15]
Operating revenues from affiliates																506	[15]	795	[15]
Exelon Generation Co L L C [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues																		7
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Revenues	1,079		1,222	1,128	1,134	1,068		1,156	1,080	1,160				4,564		4,464		5,443
Operating revenues from affiliates														4		3		2
Income taxes														268		152		239
Net income	73		126	111	98	109		126	96	(81)				408		249		379
Assets	25,392					24,118								25,392		24,118
Utility taxes														238	[5]	241	[5]	239	[5]
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues	750		693	656	993	805		728	672	895				3,094		3,100		3,186
Operating revenues from affiliates														2		1		3
Income (loss) from continuing operations before income taxes														466		557		508
Income taxes														114		162		127
Net income	98		81	84	89	102		92	72	121				352		395		381
Assets	9,943					9,617								9,943		9,617
Utility taxes														128	[5]	129	[5]	141	[5]
Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Revenues	761		697	653	1,054	794		737	653	880				3,165		3,065		2,735
Operating revenues from affiliates														25		13		10
Income (loss) from continuing operations before income taxes														351		344		11
Income taxes														140		134		7
Net income	52		46	16	85	47		50	22	77				211		210		4
Assets	8,078	[16]				7,861	[16]							8,078	[16]	7,861	[16]
Utility taxes												$ 59	[5]	$ 86	[5]	$ 82	[5]	$ 75	[5]

[1] For the years ended December 31, 2014, 2013 and 2012, utility taxes of $89 million, $79 million and $82 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $238 million, $241 million and $239 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $128 million, $129 million and $141 million, respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2014, December 31, 2013 and for the period of March 12, 2012 through December 31, 2012, utility taxes of $86 million, $82 million and $59 million are included in revenues and expenses for BGE, respectively.

[2] Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.

[3] Includes $265 million of interest expense related to the remeasurement of Exelon’s like-kind exchange tax position in the first quarter of 2013. See Note 14—Income Taxes of the Combined Notes to Consolidated Financial Statements for additional information.

[4] Exelon’s consolidated assets include $8,160 million and $1,755 million at December 31, 2014 and December 31, 2013, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $2,723 million and $658 million at December 31, 2014 and December 31, 2013, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.

[5] 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 and Comprehensive Income.

[6] The intersegment profit associated with the 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 Statement of Operations. See Note 3—Regulatory Matters for additional information.

[7] Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Regions. For the year ended December 31, 2014, intersegment revenues for Generation include revenue from sales to PECO of $198 million and sales to BGE of $387 million in the Mid-Atlantic region, and sales to ComEd of $176 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2013, intersegment revenues for Generation include revenue from sales to PECO of $405 million and sales to BGE of $455 million in the Mid-Atlantic region, and sales to ComEd of $506 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 year ended December 31, 2012, intersegment revenues for Generation 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.

[8] Amounts represent activity recorded at BGE from March 12, 2012, the closing date of the merger, through December 31, 2014.

[9] Includes all 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.

[11] 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.

[12] Generation’s consolidated assets include $8,119 million and $1,695 million at December 31, 2014 and December 31, 2013, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $2,507 million and $362 million at December 31, 2014 and December 31, 2013, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.

[13] Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information.

[14] Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[15] Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.

[16] BGE’s consolidated assets include $24 million and $31 million at December 31, 2014 and December 31, 2013, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $197 million and $269 million at December 31, 2014 and December 31, 2013, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.