Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 8,769		$ 9,002		$ 25,149		$ 23,486
Operating revenues from affiliates	0	[1]	1	[1]	2	[2]	3	[2]
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,432		1,800		4,222		4,736
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,038		1,164		3,141		3,343
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	481		451		1,461		1,272
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	428		323		1,081		873
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	314		295		753		665
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	335		238		779		686
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,028		4,271		11,437		11,575
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	723	[3]	764	[3]	2,375	[4]	1,788	[4]
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,751		5,035		13,812		13,363
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,421	[5]	1,813	[5]	4,207	[6]	4,776	[6]
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,049	[5]	1,163	[5]	3,158	[6]	3,330	[6]
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	482	[5]	455	[5]	1,469	[6]	1,278	[6]
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	434	[5]	331	[5]	1,095	[6]	906	[6]
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	308	[5]	289	[5]	749	[6]	659	[6]
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	348	[5]	271	[5]	807	[6]	728	[6]
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,042	[5]	4,322	[5]	11,485	[6]	11,677	[6]
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts	(13)		(21)		(30)		(10)
Unrealized Gain (Loss) on Securities	52		187		(47)		(366)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,751	[5]	5,035	[5]	13,812	[6]	13,363	[6]
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	709	[3],[5]	713	[3],[5]	2,327	[4],[6]	1,686	[4],[6]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	(759)	[1]	(885)	[1]	(2,262)	[2]	(2,351)	[2]
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	11		(13)		15		(40)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	(11)		1		(17)		13
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	(1)		(4)		(8)		(6)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	(6)		(8)		(14)		(33)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	6		6		4		6
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	(13)		(33)		(28)		(42)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	(14)		(51)		(48)		(102)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	14	[3]	51	[3]	48	[4]	102	[4]
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	$ 0		$ 0		$ 0		$ 0

[1] 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.

[2] 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] Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $13 million and $21 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the three months ended September 30, 2017 and 2016, respectively, unrealized mark-to-market gain of $52 million and $187 million for the three months ended September 30, 2017 and 2016, respectively, and elimination of intersegment revenues.

[4] Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $30 million and $10 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the nine months ended September 30, 2017 and 2016, respectively, unrealized mark-to-market losses of $47 million and $366 million for the nine months ended September 30, 2017 and 2016, respectively, and elimination of intersegment revenues.

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

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