Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues		$ 9,403		$ 8,768		$ 27,170		$ 25,180
Operating revenues from affiliates		0	[1]	0	[1]	0	[2]	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,456		1,432		4,179		4,222
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,117		1,038		3,593		3,141
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		699		481		2,026		1,461
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		469		427		1,269		1,110
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		444		314		930		753
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		513		335		1,088		779
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,698		4,027		13,085		11,466
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		440		480		1,944		1,859
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	140		243		339		518
Unrealized Gain (Loss) on Securities		6		52		(96)		(47)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,278		4,750		15,368		13,843
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		9,403	[4]	8,768	[4]	27,170	[5]	25,180	[5]
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,449	[6]	1,421	[6]	4,162	[7]	4,207	[7]
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,121	[6]	1,049	[6]	3,601	[7]	3,158	[7]
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		699	[6]	482	[6]	2,030	[7]	1,469	[7]
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		469	[6]	433	[6]	1,268	[7]	1,124	[7]
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		445	[6]	308	[6]	929	[7]	749	[7]
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		558	[6]	348	[6]	1,200	[7]	807	[7]
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,741	[6]	4,041	[6]	13,190	[7]	11,514	[7]
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		397	[6]	460	[6]	1,839	[7]	1,807	[7]
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts				(13)				(30)
Unrealized Gain (Loss) on Securities		71		73		(104)		(161)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,278	[6]	4,750	[6]	15,368	[7]	13,843	[7]
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		140	[6],[8]	249	[6],[8]	339	[3],[7]	522	[3],[7]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(780)	[4]	(762)	[4]	(2,436)	[5]	(2,267)	[5]
Operating revenues from affiliates		(779)	[1]	(759)	[1]	(2,430)	[2]	(2,262)	[2]
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7		11		17		15
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(4)		(11)		(8)		(17)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0		(1)		(4)		(8)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0		(6)		1		(14)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(1)		6		1		4
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(45)		(13)		(112)		(28)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(43)		(14)		(105)		(48)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		43		20		105		52
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[3]	0		(6)		0		(4)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0		0		0		0
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,397	[6]	1,397	[6]	3,971	[7]	4,260	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,095	[6]	982	[6]	3,432	[7]	2,948	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		666	[6]	504	[6]	1,943	[7]	1,555	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		475	[6]	454	[6]	1,305	[7]	1,161	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		156	[6]	164	[6]	470	[7]	520	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		293	[6]	167	[6]	713	[7]	439	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,082	[6]	3,668	[6]	11,834	[7]	10,883	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		200	[6]	226	[6]	1,016	[7]	1,237	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		4,412	[6]	4,101	[6]	13,235	[7]	12,708	[7]
Revenue from Contract with Customer [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		130	[6],[8]	207	[6],[8]	385	[3],[7]	588	[3],[7]
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		52	[6],[9]	24	[6],[9]	191	[7],[10]	(53)	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		26	[6],[9]	67	[6],[9]	169	[7],[10]	210	[7],[10]
Other [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		33	[6],[9]	(22)	[6],[9]	87	[7],[10]	(86)	[7],[10]
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		(6)	[6],[9]	(21)	[6],[9]	(37)	[7],[10]	(37)	[7],[10]
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		289	[6],[9]	144	[6],[9]	459	[7],[10]	229	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		265	[6],[9]	181	[6],[9]	487	[7],[10]	368	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		659	[6],[9]	373	[6],[9]	1,356	[7],[10]	631	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		197	[6],[9]	234	[6],[9]	823	[7],[10]	570	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		866	[6],[9]	649	[6],[9]	2,133	[7],[10]	1,135	[7],[10]
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		$ 10	[6],[8],[9]	$ 42	[6],[8],[9]	$ (46)	[3],[7],[10]	$ (66)	[3],[7],[10]

[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 $30 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, unrealized mark-to-market losses of $96 million and $47 million for the nine months ended September 30, 2018 and 2017, respectively, and elimination of intersegment revenues.

[4] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended September 30, 2018 and 2017.

[5] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the nine months ended September 30, 2018 and 2017.

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

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

[8] Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $13 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, unrealized mark-to-market gains of $6 million and $52 million for the three months ended September 30, 2018 and 2017, respectively, and elimination of intersegment revenues.

[9] Includes revenues from derivatives and leases.

[10] Includes revenues from derivatives and leases.