Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 33,039	$ 34,438	$ 35,978
Depreciation and amortization		5,014	4,252	4,353
Operating Expenses		30,240	30,096	32,143
Interest expense, net		1,635	1,616	1,554
Income (loss) before income taxes		2,333	3,985	2,225
Income taxes		373	774	118
Net income (loss)		1,954	3,028	2,079
Capital expenditures		8,048	7,248	7,594
Total assets	[1]	129,317	124,977
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		17,603	18,924	20,437
Operating revenues from affiliates		1,211	1,172	1,268
Income (loss) before income taxes		836	1,917	365
Income taxes		249	516	(108)
Net income (loss)		579	1,217	443
Capital expenditures		1,747	1,845	2,242
Total assets	[2]	48,094	48,995
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues		3,058	3,100	3,038
Operating revenues from affiliates		9	6	8
Income (loss) before income taxes		417	593	466
Income taxes		(30)	65	6
Net income (loss)		447	528	460
Capital expenditures		1,147	939	849
Total assets		12,531	11,469
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		8	5	7
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		4,663	4,806	4,798
Operating revenues from affiliates		17	14	15
Income (loss) before income taxes		418	514	425
Income taxes		(77)	38	33
Net income (loss)		495	477	393
Capital expenditures		1,604	1,355	1,375
Total assets		23,736	22,719
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		33,039	34,438	35,978
Net income (loss)		1,954	3,028	2,079
Total assets		129,317	124,977
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(3,322)	(3,166)	(3,294)
Operating revenues from affiliates		4	2	1
Depreciation and amortization		0	0	0
Operating Expenses		(3,270)	(3,154)	(3,341)
Interest expense, net		(3)	0	0
Income (loss) before income taxes		0	(2)	(1)
Income taxes		0	0	0
Net income (loss)		0	(2)	(1)
Capital expenditures		0	0	0
Total assets		(10,165)	(10,089)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		(374)	(396)	(437)
Operating revenues from affiliates		(375)	(397)	(437)
Depreciation and amortization		0	0	0
Operating Expenses		(375)	(396)	(435)
Interest expense, net		0	1	0
Income (loss) before income taxes		0	0	0
Income taxes		0	0	0
Net income (loss)		0	0	0
Capital expenditures		0	0	0
Total assets		(33)	(40)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		17,603	18,924	20,437
Depreciation and amortization		2,123	1,535	1,797
Operating Expenses		17,358	17,628	19,510
Interest expense, net		357	429	432
Income (loss) before income taxes		836	1,917	365
Income taxes		249	516	(108)
Net income (loss)		579	1,217	443
Capital expenditures		1,747	1,845	2,242
Total assets		48,094	48,995
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1,211	1,172	1,269
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		5,904	5,747	5,882
Depreciation and amortization		1,133	1,033	940
Operating Expenses		4,950	4,580	4,741
Interest expense, net		382	359	347
Income (loss) before income taxes		615	851	832
Income taxes		177	163	168
Net income (loss)		438	688	664
Capital expenditures		2,217	1,915	2,126
Total assets		34,466	32,765
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		37	30	27
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		3,058	3,100	3,038
Depreciation and amortization		347	333	301
Operating Expenses		2,512	2,388	2,452
Interest expense, net		147	136	129
Income (loss) before income taxes		417	593	466
Income taxes		(30)	65	6
Net income (loss)		447	528	460
Capital expenditures		1,147	939	849
Total assets		12,531	11,469
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		9	6	8
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		3,098	3,106	3,169
Depreciation and amortization		550	502	483
Operating Expenses		2,598	2,574	2,696
Interest expense, net		133	121	106
Income (loss) before income taxes		390	439	387
Income taxes		41	79	74
Net income (loss)		349	360	313
Capital expenditures		1,247	1,145	959
Total assets		11,650	10,634
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		20	26	29
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		4,663	4,806	4,798
Depreciation and amortization		782	754	740
Operating Expenses		4,045	4,084	4,156
Interest expense, net		268	263	261
Income (loss) before income taxes		418	514	425
Income taxes		(77)	38	33
Net income (loss)		495	477	393
Capital expenditures		1,604	1,355	1,375
Total assets		23,736	22,719
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		17	14	15
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		2,149	2,260	2,232
Depreciation and amortization		377	374	385
Operating Expenses		1,799	1,899	1,919
Interest expense, net		138	133	128
Income (loss) before income taxes		259	259	216
Income taxes		(7)	16	11
Net income (loss)		266	243	205
Capital expenditures		773	626	656
Total assets		9,264	8,661
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7	5	6
Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,271	1,306	1,332
Depreciation and amortization		191	184	182
Operating Expenses		1,120	1,089	1,143
Interest expense, net		61	61	58
Income (loss) before income taxes		100	169	142
Income taxes		(25)	22	22
Net income (loss)		125	147	120
Capital expenditures		424	348	364
Total assets		5,140	4,830
Delmarva Power & Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		9	7	8
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,245	1,240	1,236
Depreciation and amortization		180	157	136
Operating Expenses		1,123	1,089	1,087
Interest expense, net		59	58	64
Income (loss) before income taxes		71	99	87
Income taxes		(41)	0	12
Net income (loss)		112	99	75
Capital expenditures		401	375	335
Total assets		4,286	3,933
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		4	3	3
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenues		2,035	1,921	1,948
Depreciation and amortization		79	95	92
Operating Expenses		2,047	1,996	1,929
Interest expense, net		351	308	279
Income (loss) before income taxes		(343)	(327)	(249)
Income taxes		13	(87)	(55)
Net income (loss)		(354)	(240)	(193)
Capital expenditures		86	49	43
Total assets		9,005	8,484
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		372	396	435
Depreciation and amortization		34	39	37
Operating Expenses		378	403	442
Interest expense, net		10	10	11
Income (loss) before income taxes		(12)	(13)	(20)
Income taxes		(4)	0	(12)
Net income (loss)		(8)	(12)	(7)
Capital expenditures		6	6	20
Total assets		5,079	5,335
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member] | Revision of Prior Period, Adjustment [Member]
Segment Reporting Information [Line Items]
Income (loss) before income taxes			489	408
Total assets			5,700
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2,024	1,913	1,942
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		372	396	435
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(3,314)	(3,159)	(3,289)
Electricity, Generation [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		13,864	15,120	16,155
Electricity, Generation [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(1,196)	(1,165)	(1,256)
Electricity, Generation [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		15,060	16,285	17,411
Electricity, Generation [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Electricity, Generation [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Electricity, Generation [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Electricity, Generation [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Electricity, Generation [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Oil and Gas, Purchased [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,000	2,147	2,710
Oil and Gas, Purchased [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(3)	(1)	(8)
Oil and Gas, Purchased [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,003	2,148	2,718
Oil and Gas, Purchased [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Oil and Gas, Purchased [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Oil and Gas, Purchased [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Oil and Gas, Purchased [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Oil and Gas, Purchased [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Other Revenues [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		536	487	303
Other Revenues [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		(4)	(4)	(5)
Other Revenues [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		540	491	308
Other Revenues [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0	0	0
Other Revenues [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0	0	0
Other Revenues [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0	0	0
Other Revenues [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0	0	0
Other Revenues [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0	0	0
Electricity, US Regulated [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,519	2,505	2,469
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		4,463	4,639	4,609
Electricity, US Regulated [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		15,207	15,195	15,337
Electricity, US Regulated [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(61)	(47)	(45)
Electricity, US Regulated [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(18)	(13)	(17)
Electricity, US Regulated [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		5,904	5,747	5,882
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,543	2,490	2,470
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,336	2,379	2,428
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		4,485	4,626	4,602
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,149	2,260	2,232
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,109	1,139	1,151
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,245	1,240	1,236
Electricity, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Electricity, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		514	610	568
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		162	167	181
Natural Gas, US Regulated [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,432	1,489	1,470
Natural Gas, US Regulated [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(7)	(15)	(20)
Natural Gas, US Regulated [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		515	610	568
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		762	727	741
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		162	167	181
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		162	167	181
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Natural Gas, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	3
Service, Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(2,051)	(1,934)	(1,960)
Service, Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(356)	(383)	(420)
Service, Other [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		16	13	15
Service, Other [Member] | Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0	0	0
Service, Other [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		2,035	1,921	1,948
Service, Other [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		$ 372	$ 396	$ 435

[1] Exelon’s consolidated assets include $10,200 million and $9,532 million at December 31, 2020 and 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,598 million and $3,473 million at December 31, 2020 and 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 23–Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $10,182 million and $9,512 million at December 31, 2020 and 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,572 million and $3,429 million at December 31, 2020 and 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 23–Variable Interest Entities for additional information.