Segment Information Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues		$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747	$ 35,985	$ 33,565	$ 31,366
Revenue from Related Parties											0	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,487	5,540	6,179
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,706	4,181	4,412
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										2,841	2,002	1,769
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										1,687	1,550	1,166
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										1,133	962	837
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues										1,494	1,049	907
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										17,348	15,284	15,270
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues										2,780	2,628	2,281
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									309	588	206
Unrealized Gain (Loss) on Securities										(262)	(131)	(500)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										20,437	18,500	17,757
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									35,985	33,567	31,365
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									5,474	5,515	6,212
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,717	4,206	4,402
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,845	2,010	1,778
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,687	1,567	1,208
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,132	958	831
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,556	1,076	969
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									17,411	15,332	15,400
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,718	2,575	2,146
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts											(38)	52
Unrealized Gain (Loss) on Securities										(319)	(175)	(41)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									20,437	18,500	17,757
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(1)	7	10
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									308	593	211
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									(3,294)	(3,025)	(3,164)
Revenue from Related Parties	[4]									1	2	5
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										13	25	(33)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(11)	(25)	10
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(4)	(8)	(9)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										0	(17)	(42)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										1	4	6
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(62)	(27)	(62)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(63)	(48)	(130)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										62	53	135
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[1]									1	(5)	(5)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										0	0	0
Contracts with Customers [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									5,241	5,523	6,182
Contracts with Customers [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,527	3,923	4,007
Contracts with Customers [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,660	2,064	1,953
Contracts with Customers [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,723	1,605	1,198
Contracts with Customers [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									572	641	810
Contracts with Customers [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									870	594	670
Contracts with Customers [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									15,593	14,350	14,820
Contracts with Customers [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,524	1,658	1,953
Contracts with Customers [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									17,627	16,752	17,529
Contracts with Customers [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									510	744	756
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									233	(8)	30
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									190	283	395
Other [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									185	(54)	(175)
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									(36)	(38)	10
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									560	317	21
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									686	482	299
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									1,818	982	580
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									1,194	917	193
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									2,810	1,748	228
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3],[5]									$ (202)	$ (151)	$ (545)

[1] Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $38 million and $52 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 and 2016, respectively, unrealized mark-to-market losses of $262 million, $131 million, and $500 million in 2018, 2017, and 2016, respectively, and elimination of intersegment revenues.

[2] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.

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

[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 authoritative guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

[5] Includes revenues from derivatives and leases.