Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Segment Reporting Information [Line Items]
Revenues		$ 6,514	[1]	$ 6,024	[1]	$ 15,345	[2]	$ 13,261	[2]
Revenue from Related Parties		1	[3]	0	[3]	3		0
Net income (loss)		633		557		1,372		651
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Commodity Contracts		25		(83)		179		(843)
Revenues		4,232		3,789		10,074		8,179
Revenue from Related Parties		153		201		365		535
Net income (loss)		390		372		875		188
Amortization of Intangible Assets		17		88		(22)		180
Exelon Generation Co L L C [Member] | Sales Revenue, Goods, Net [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Commodity Contracts		235		(14)		(397)		744
Amortization of Intangible Assets		14		50		24		92
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		0
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(495)	[1]	(531)	[1]	(1,029)	[2]	(1,155)	[2]
Revenue from Related Parties		(493)	[3]	(531)	[3]	(1,026)		(1,155)
Net income (loss)		(1)		0		(3)		0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,346		1,277		2,859		2,695
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,336		1,272		2,853		2,713
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		10		5		6		(18)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,206		981		2,482		2,251
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,205		981		2,480		2,239
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		1		0		2		12
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		367		212		1,226		761
Generation New England [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		366		211		1,224		756
Generation New England [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		1		1		2		5
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		218		194		528		381
Generation New York [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		222		194		532		384
Generation New York [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(4)		0		(4)		(3)
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		192		197		372		440
Generation ERCOT [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		194		198		376		441
Generation ERCOT [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(2)		(1)		(4)		(1)
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		289		308		503		649
Generation Other Regions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		294		314		506		648
Generation Other Regions [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(5)		(6)		(3)		1
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		3,618		3,169		7,970		7,177
Generation Reportable Segments Total [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	3,617		3,170		7,971		7,181
Generation Reportable Segments Total [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		1		(1)		(1)		(4)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		614		620		2,104		1,002
Generation All Other Segments [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		615		619	[4],[5]	2,103		998
Generation All Other Segments [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(1)		1	[5]	1		4
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,232		3,789		10,074		8,179
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		4,232	[1]	3,789	[1]	10,074	[2],[6],[7]	8,179	[2],[6],[7]
Revenue from Related Parties		152	[3]	201	[3]	362	[6],[7]	517	[6],[7]
Net income (loss)		390		372		875	[6],[7]	188	[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		$ 6		$ 65		$ 15		$ 173

[1] (c)For the three months ended June 30, 2015 and 2014, utility taxes of $24 million and $21 million, respectively, are included in revenues and expenses for Generation. For the three months ended June 30, 2015 and 2014, utility taxes of $55 million and $56 million, respectively, are included in revenues and expenses for ComEd. For the three months ended June 30, 2015 and 2014, utility taxes of $32 million and $30 million, respectively, are included in revenues and expenses for PECO. For the three months ended June 30, 2015 and 2014, utility taxes of $21 million and $19 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 $17 million decrease to revenues and an $88 million decrease to revenues for the amortization of intangible assets related to commodity contracts for the three months ended June 30, 2015 and 2014, respectively, unrealized mark-to-market gains of $25 million and losses of $83 million for the three months ended June 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 six months ended June 30, 2015 include revenue from sales to PECO of $112 million and sales to BGE of $235 million in the Mid-Atlantic region, and sales to ComEd of $15 million in the Midwest. For the six months ended June 30, 2014, intersegment revenues for Generation include revenue from sales to PECO of $137 million and sales to BGE of $207 million in the Mid-Atlantic region, and sales to ComEd of $173 million in the Midwest region.

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