Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues		$ 7,401	[1]	$ 6,912	[1]	$ 22,746	[2]	$ 20,173	[2]
Net income (loss)		587		1,074		1,959		1,725
Operating revenues from affiliates		2	[3]	0	[3]	3		0
Assets		95,128				95,128				$ 86,814
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		4,768	[1]	4,412	[1]	14,841	[2],[4],[5]	12,591	[2],[4],[5]
Net income (loss)		332		849		1,208	[4],[5]	1,037	[4],[5]
Operating revenues from affiliates		205	[3]	112	[3]	567	[4],[5]	630	[4],[5]
Assets		46,479				46,479				45,348
Utility Taxes		28		22		79		67
Operating Segments [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Revenues		1,376	[1]	1,222	[1]	3,709	[2]	3,484	[2]
Net income (loss)		149		126		339		335
Operating revenues from affiliates		1	[3]	1	[3]	3		2
Assets		26,129				26,129				25,392
Utility Taxes		63		61		180		180
Operating Segments [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues		740	[1]	693	[1]	2,386	[2]	2,343	[2]
Net income (loss)		90		81		299		255
Operating revenues from affiliates		1	[3]	0	[3]	1		1
Assets		10,072				10,072				9,943
Utility Taxes		37		34		104		99
Operating Segments [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Revenues		725	[1]	697	[1]	2,388	[2]	2,404	[2]
Net income (loss)		54		49		212		156
Operating revenues from affiliates		3	[3]	3	[3]	10		21
Assets		8,134				8,134				8,078
Utility Taxes		23		21		67		64
Operating Segments [Member] | PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		61		28		173		165
Operating Segments [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		141		83		376		290
Operating Segments [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		1		17		175
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues		348	[1],[6]	305	[1],[6]	1,007	[2],[7]	924	[2],[7]
Net income (loss)		(36)	[6]	(31)	[6]	(96)	[7]	(58)	[7]
Operating revenues from affiliates		347	[3],[6]	302	[3],[6]	1,003	[7]	920	[7]
Assets	[6]	16,256				16,256				9,794
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		0
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues		(556)	[1]	(417)	[1]	(1,585)	[2]	(1,573)	[2]
Net income (loss)		(2)		0		(3)		0
Operating revenues from affiliates		(555)	[3]	$ (418)	[3]	(1,581)		$ (1,574)
Assets		$ (11,942)				$ (11,942)				$ (11,741)

[1] (c)For the three months ended September 30, 2015 and 2014, utility taxes of $28 million and $22 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2015 and 2014, utility taxes of $63 million and $61 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2015 and 2014, utility taxes of $37 million and $34 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2015 and 2014, utility taxes of $23 million and $21 million, respectively, are included in revenues and expenses for BGE.

[2] (d)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.

[3] (d)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] (a)Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. Intersegment revenues for Generation for the nine months ended September 30, 2015 include revenue from sales to PECO of $173 million and sales to BGE of $376 million in the Mid-Atlantic region, and sales to ComEd of $17 million in the Midwest. For the nine months ended September 30, 2014, intersegment revenues for Generation 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 region.

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

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

[7] (c)For the nine months ended September 30, 2015 and 2014, utility taxes of $79 million and $67 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2015 and 2014, utility taxes of $180 million and $180 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2015 and 2014, utility taxes of $104 million and $99 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2015 and 2014, utility taxes of $67 million and $64 million, respectively, are included in revenues and expenses for BGE.