Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues		$ 6,702	$ 7,401	$ 6,514	$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237	$ 29,447	$ 27,429	$ 24,888
Revenue from Related Parties										9	23	70
Amortization of intangible assets related to commodity contracts										7	289	767
Net mark-to market gains (losses)										357	(693)	507
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,900	5,259	5,204
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,710	4,475	4,270
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										2,212	1,422	1,237
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										985	843	714
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										857	935	1,216
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									1,102	1,309	968
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										15,766	14,243	13,609
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									3,369	3,150	2,021
Net mark-to market gains (losses)										257	(591)	504
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										19,135	17,393	15,630
Scenario, Adjustment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties											(284)	(252)
Scenario, Adjustment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties											284	252
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									5,974	5,414	5,261
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,712	4,488	4,298
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,217	1,468	1,279
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									996	846	717
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									863	938	1,223
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									1,182	1,379	1,084
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									15,944	14,533	13,862
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2],[3]									3,191	2,860	1,768
Net mark-to market gains (losses)										203	(174)	220
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									19,135	17,393	15,630
Operating Segments [Member] | Scenario, Adjustment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues											284	252
Operating Segments [Member] | Scenario, Adjustment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues											(284)	(252)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[4]									5	6	14
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(74)	(155)	(57)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(2)	(13)	(28)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(5)	(46)	(42)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(11)	(3)	(3)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(6)	(3)	(7)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[1]									(80)	(70)	(116)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(178)	(290)	(253)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[2]									178	290	253
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										$ 0	$ 0	$ 0

[1] (b)Includes all wholesale and retail electric sales to third parties and affiliated sales to ComEd, PECO and BGE.

[2] (c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $7 million increase to revenues, a $289 million decrease to revenues, and a $767 million decrease to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015, 2014, and 2013, respectively, unrealized mark-to-market gains of $203 million, losses of $174 million, and gains of $220 million for the years ended December 31, 2015, 2014, and 2013, respectively, and elimination of intersegment revenues.

[3] (a)On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues are included on a fully consolidated basis.

[4] 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.