Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Competitive businesses other revenues		$ 132			$ 194			$ 552	$ 432
Revenues		8,853			8,929			24,925	26,096
Revenue from Related Parties		1			0			4	0
Depreciation and Amortization		1,289			1,083			3,312	3,237
Operating Expenses		8,087			7,559			22,387	22,703
Interest expense, net		404			409			1,241	1,221
Income (Loss) before income taxes		786			1,102			1,665	3,028
Income taxes		216			172			141	626
Net income (loss)		569	$ 574	$ 376	760	$ 494	$ 966	1,519	2,220
Capital expenditures		1,833			1,687			5,606	5,259
Assets	[1]	127,767						127,767		$ 124,977
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		4,659			4,774			13,272	14,280
Revenue from Related Parties		331			275			932	844
Income (Loss) before income taxes		219			501			532	1,355
Income taxes		100			87			41	388
Net income (loss)		117	529	(161)	244	118	422	485	784
Capital expenditures								1,212	1,282
Assets	[2]	47,372						47,372		48,995
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		1,368			1,380			3,554	3,700
Revenue from Related Parties		6			4			13	11
Income (Loss) before income taxes		215			203			340	436
Income taxes		(1)			14			(77)	25
Net income (loss)		216	$ 94	$ 108	189	$ 106	$ 117	418	412
Capital expenditures								1,072	1,006
Assets	[3]	23,394						23,394		22,719
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		71			83			241	266
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		68			43			146	123
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		84			65			252	199
Operating Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		31			(9)			(15)	4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		(3)			(1)			(5)	(4)
Revenues		(845)			(763)			(2,430)	(2,296)
Revenue from Related Parties		(845)			(764)			(2,430)	(2,300)
Depreciation and Amortization		0			0			0	0
Operating Expenses		(833)			(759)			(2,397)	(2,291)
Interest expense, net		0			0			0	0
Income (Loss) before income taxes		0			0			0	0
Income taxes		0			0			0	0
Net income (loss)		0			0			0	0
Capital expenditures		0			0			0	0
Assets		(10,016)						(10,016)		(10,089)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		(91)			(92)			(281)	(298)
Revenue from Related Parties		(91)			(93)			(281)	(298)
Depreciation and Amortization		0			0			0	0
Operating Expenses		(91)			(94)			(281)	(298)
Interest expense, net		0			0			0	0
Income (Loss) before income taxes		0			0			0	0
Income taxes		0			0			0	0
Net income (loss)		0			0			0	0
Capital expenditures		0			0			0	0
Assets		(265)						(265)		(40)
Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		135			195			557	436
Revenues		4,659			4,774			13,272	14,280
Depreciation and Amortization		558			407			1,161	1,221
Operating Expenses		4,727			4,274			12,674	13,333
Interest expense, net		80			109			277	336
Income (Loss) before income taxes		219			501			532	1,355
Income taxes		100			87			41	388
Net income (loss)		117			244			485	784
Capital expenditures		282			392			1,212	1,282
Assets		47,372						47,372		48,995
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		331			275			932	844
Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0			0			0	0
Revenues		1,643			1,583			4,499	4,342
Depreciation and Amortization		294			259			841	767
Operating Expenses		1,302			1,256			3,798	3,431
Interest expense, net		95			91			287	268
Income (Loss) before income taxes		256			245			446	674
Income taxes		60			45			142	130
Net income (loss)		196			200			304	544
Capital expenditures		554			452			1,583	1,413
Assets		34,243						34,243		32,765
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		15			4			31	13
PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0			0			0	0
Revenues		813			778			2,306	2,333
Depreciation and Amortization		85			83			259	247
Operating Expenses		658			595			1,900	1,783
Interest expense, net		39			33			108	100
Income (Loss) before income taxes		122			154			310	461
Income taxes		(16)			14			(7)	51
Net income (loss)		138			140			317	410
Capital expenditures		312			228			824	675
Assets		12,334						12,334		11,469
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		3			1			7	4
Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0			0			0	0
Revenues		731			703			2,284	2,327
Depreciation and Amortization		133			116			405	368
Operating Expenses		642			612			1,903	1,936
Interest expense, net		34			31			99	89
Income (Loss) before income taxes		61			67			299	320
Income taxes		8			12			26	59
Net income (loss)		53			55			273	261
Capital expenditures		290			300			838	842
Assets		11,370						11,370		10,634
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		6			6			16	18
Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0			0			0	0
Revenues		1,368			1,380			3,554	3,700
Depreciation and Amortization		200			193			585	562
Operating Expenses		1,102			1,124			3,057	3,106
Interest expense, net		67			66			201	197
Income (Loss) before income taxes		215			203			340	436
Income taxes		(1)			14			(77)	25
Net income (loss)		216			189			418	412
Capital expenditures		386			308			1,072	1,006
Assets		23,394						23,394		22,719
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		6			4			13	11
Potomac Electric Power Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues		611			642			1,650	1,748
Depreciation and Amortization		96			95			282	281
Operating Expenses		465			515			1,364	1,444
Interest expense, net		35			33			103	100
Income (Loss) before income taxes		121			103			211	226
Income taxes		3			5			(16)	9
Net income (loss)		118			98			227	217
Capital expenditures		188			157			512	455
Assets		9,227						9,227		8,661
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		3			2			6	5
Delmarva Power and Light Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues		337			319			954	987
Depreciation and Amortization		48			46			143	138
Operating Expenses		296			268			843	820
Interest expense, net		15			15			47	45
Income (Loss) before income taxes		28			38			71	132
Income taxes		1			5			(20)	16
Net income (loss)		27			33			91	116
Capital expenditures		94			85			278	245
Assets		4,992						4,992		4,830
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		3			1			7	5
Atlantic City Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues		420			419			952	966
Depreciation and Amortization		48			43			134	114
Operating Expenses		338			340			847	838
Interest expense, net		15			15			45	44
Income (Loss) before income taxes		68			65			67	89
Income taxes		(7)			2			(39)	2
Net income (loss)		75			63			106	87
Capital expenditures		103			73			281	300
Assets		4,201						4,201		3,933
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		1			1			3	2
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0			0			0	0
Revenues		484			474			1,440	1,410
Depreciation and Amortization		19			25			61	72
Operating Expenses		489			457			1,452	1,405
Interest expense, net		89			79			269	231
Income (Loss) before income taxes		(87)			(68)			(262)	(218)
Income taxes		65			0			16	(27)
Net income (loss)		(151)			(68)			(278)	(191)
Capital expenditures		9			7			77	41
Assets		9,070						9,070		8,484
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		91			92			279	297
Depreciation and Amortization		8			9			26	29
Operating Expenses		94			95			284	302
Interest expense, net		2			3			6	8
Income (Loss) before income taxes		(2)			(3)			(9)	(11)
Income taxes		2			2			(2)	(2)
Net income (loss)		(4)			(5)			(6)	(8)
Capital expenditures		1			(7)			1	6
Assets		5,239						5,239		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					195				422
Assets										$ 5,700
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		485			474			1,435	1,410
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		90			93			278	297
Electricity, Generation [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		3,875			4,039			10,447	11,525
Electricity, Generation [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(326)			(275)			(920)	(840)
Electricity, Generation [Member] | Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		4,201			4,314			11,367	12,365
Electricity, Generation [Member] | Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Electricity, Generation [Member] | PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Electricity, Generation [Member] | Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Electricity, Generation [Member] | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			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	0
Oil and Gas, Purchased [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		323			266			1,345	1,479
Oil and Gas, Purchased [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			1			(3)	0
Oil and Gas, Purchased [Member] | Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		323			265			1,348	1,479
Oil and Gas, Purchased [Member] | Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Oil and Gas, Purchased [Member] | PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Oil and Gas, Purchased [Member] | Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Oil and Gas, Purchased [Member] | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			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	0
Electricity, US Regulated
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		4,365			4,268			11,585	11,609
Electricity, US Regulated | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,308			1,365			3,440	3,570
Electricity, US Regulated | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(22)			(7)			(50)	(25)
Electricity, US Regulated | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(6)			(3)			(15)	(10)
Electricity, US Regulated | Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Electricity, US Regulated | Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,643			1,583			4,499	4,342
Electricity, US Regulated | PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		759			716			1,948	1,901
Electricity, US Regulated | Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		646			619			1,763	1,817
Electricity, US Regulated | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,339			1,357			3,425	3,574
Electricity, US Regulated | Potomac Electric Power Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		611			642			1,650	1,748
Electricity, US Regulated | Delmarva Power and Light Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		314			299			838	871
Electricity, US Regulated | Atlantic City Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		420			419			952	966
Electricity, US Regulated | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Electricity, US Regulated | 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	(1)
Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		159			163			990	1,046
Natural Gas, US Regulated | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		23			20			116	115
Natural Gas, US Regulated | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(3)			(3)			(5)	(12)
Natural Gas, US Regulated | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Natural Gas, US Regulated | Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Natural Gas, US Regulated | Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Natural Gas, US Regulated | PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		54			62			358	432
Natural Gas, US Regulated | Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		85			84			521	510
Natural Gas, US Regulated | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		23			20			116	116
Natural Gas, US Regulated | Potomac Electric Power Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Natural Gas, US Regulated | Delmarva Power and Light Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		23			20			116	116
Natural Gas, US Regulated | Atlantic City Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Natural Gas, US Regulated | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Natural Gas, US Regulated | 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	0
Service, Other [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(1)			(1)			6	5
Service, Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(491)			(478)			(1,447)	(1,415)
Service, Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(85)			(89)			(266)	(288)
Service, Other [Member] | Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Service, Other [Member] | Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Service, Other [Member] | PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Service, Other [Member] | Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Service, Other [Member] | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		6			3			13	10
Service, Other [Member] | Potomac Electric Power Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Service, Other [Member] | Delmarva Power and Light Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			0			0	0
Service, Other [Member] | Atlantic City Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0			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		484			474			1,440	1,410
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		$ 91			$ 92			$ 279	$ 298

[1] Exelon’s consolidated assets include $10,102 million and $9,532 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,531 million and $3,473 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 16 — Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $10,082 million and $9,512 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,499 million and $3,429 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 16 — Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $20 million and $20 million at September 30, 2020 and December 31, 2019, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $32 million and $44 million at September 30, 2020 and December 31, 2019, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 16 — Variable Interest Entities for additional information.