Segment Information Segment Information- Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues		$ 8,381	$ 8,769	$ 7,623	$ 8,757	$ 7,875	$ 9,002	$ 6,910	$ 7,573	$ 33,531	$ 31,360	$ 29,447
Operating revenues from affiliates										7	10	9
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,540	6,179	5,900
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,181	4,412	4,710
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										2,002	1,769	2,212
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										1,518	1,156	985
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										962	837	857
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues										1,049	907	1,102
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										15,252	15,260	15,766
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									3,214	2,491	3,369
Unrealized Gain (Loss) on Securities										(131)	(500)	203
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										18,466	17,751	19,135
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									5,515	6,212	5,974
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									4,206	4,402	4,712
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									2,010	1,778	2,217
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									1,535	1,198	996
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									958	831	863
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									1,076	969	1,182
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									15,300	15,390	15,944
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts										(38)	(52)	7
Unrealized Gain (Loss) on Securities										(175)	(41)	257
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									18,466	17,751	19,135
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[2]									3,166	2,361	3,191
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[3]									2	5	5
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										25	(33)	(74)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(25)	10	(2)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(8)	(9)	(5)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(17)	(42)	(11)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										4	6	(6)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(27)	(62)	(80)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(48)	(130)	(178)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]									48	130	178
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										$ 0	$ 0	$ 0

[1] Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $38 million decrease to revenues, a $52 million decrease to revenues, and a $7 million increase to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2017, 2016, and 2015, respectively, unrealized mark-to-market losses of $131 million, losses of $500 million, and gains of $203 million for the years ended December 31, 2017, 2016, and 2015, respectively, and elimination of intersegment revenues.

[2] Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants

[3] 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.