Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Segment Reporting Information [Line Items]
Revenues		$ 7,401	[1]	$ 6,912	[1]	$ 22,746	[2]	$ 20,173	[2]
Revenue from Related Parties		2	[3]	0	[3]	3		0
Net income (loss)		587		1,074		1,959		1,725
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Commodity Contracts		(7)		271		171		(572)
Revenues		4,768		4,412		14,841		12,591
Revenue from Related Parties		206		112		571		647
Net income (loss)		332		849		1,208		1,037
Amortization of Intangible Assets		(3)		(22)		(19)		(203)
Exelon Generation Co L L C [Member] | Sales Revenue, Goods, Net [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Commodity Contracts		(139)		267		(258)		477
Amortization of Intangible Assets		(4)		(15)		(20)		(78)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		0
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(556)	[1]	(417)	[1]	(1,585)	[2]	(1,573)	[2]
Revenue from Related Parties		(555)	[3]	(418)	[3]	(1,581)		(1,574)
Net income (loss)		(2)		0		(3)		0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,632		1,289		4,491		3,984
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,622		1,285		4,475		3,998
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		10		4		16		(14)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,151		1,061		3,633		3,313
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,150		1,062		3,630		3,302
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		1		(1)		3		11
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		520		272		1,746		1,033
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		519		272		1,743		1,028
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		1		0		3		5
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		250		232		778		613
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		254		230		786		614
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(4)		2		(8)		(1)
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		316		302		687		741
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		317		303		691		743
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(1)		(1)		(4)		(2)
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		376		375		880		1,023
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		383		381		891		1,027
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(7)		(6)		(11)		(4)
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,245		3,531		12,215		10,707
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,245		3,533		12,216		10,712
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		0		(2)		(1)		(5)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		523		881		2,626		1,884
Generation All Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		523		879	[4],[5]	2,625		1,879
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		0		2	[5]	1		5
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,768		4,412		14,841		12,591
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues				0		0		0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		4,768	[1]	4,412	[1]	14,841	[2],[6],[7]	12,591	[2],[6],[7]
Revenue from Related Parties		205	[3]	112	[3]	567	[6],[7]	630	[6],[7]
Net income (loss)		332		849		1,208	[6],[7]	1,037	[6],[7]
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		$ 2		$ 1		$ 17		$ 175

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

[5] (c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $3 million decrease to revenues and a $22 million decrease to revenues for the amortization of intangible assets related to commodity contracts for the three months ended September 30, 2015 and 2014, respectively, unrealized mark-to-market losses of $7 million and gains of $271 million for the three months ended September 30, 2015 and 2014, respectively, and the elimination of intersegment revenues.

[6] (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.

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