Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Competitive businesses other revenues		$ 112		$ 158		$ 421	$ 238
Revenues		7,322		7,689		16,069	17,166
Revenue from Related Parties		1		0		2	0
Depreciation and Amortization		1,001		1,079		2,023	2,154
Operating Expenses		6,769		6,881		14,298	15,142
Interest expense, net		427		409		837	813
Income (Loss) before income taxes		794		644		879	1,926
Income taxes		219		144		(75)	454
Net income (loss)		574	$ 376	494	$ 966	950	1,460
Capital expenditures		1,757		1,702		3,773	3,572
Assets	[1]	126,313				126,313		$ 124,977
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		3,880		4,210		8,613	9,506
Revenue from Related Parties		271		252		601	569
Income (Loss) before income taxes		860		202		313	854
Income taxes		329		78		(59)	301
Net income (loss)		529	(161)	118	422	368	540
Capital expenditures						930	890
Assets	[2]	47,003				47,003		48,995
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		1,016		1,091		2,187	2,319
Revenue from Related Parties		3		3		7	7
Income (Loss) before income taxes		7		112		126	234
Income taxes		(87)		6		(76)	11
Net income (loss)		94	$ 108	106	$ 117	202	223
Capital expenditures						686	698
Assets	[3]	23,004				23,004		22,719
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		80		89		170	183
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		41		35		78	80
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		70		57		169	133
Operating Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(64)		(3)		(47)	12
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		(1)		(1)		(2)	(2)
Revenues		(760)		(751)		(1,587)	(1,537)
Revenue from Related Parties		(760)		(750)		(1,585)	(1,534)
Depreciation and Amortization		0		0		0	0
Operating Expenses		(748)		(744)		(1,564)	(1,526)
Interest expense, net		0		0		0	0
Income (Loss) before income taxes		1		0		2	0
Income taxes		0		0		0	0
Net income (loss)		1		0		2	0
Capital expenditures		0		0		0	0
Assets		(10,025)				(10,025)		(10,089)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		(98)		(98)		(190)	(206)
Revenue from Related Parties		(98)		(99)		(190)	(205)
Depreciation and Amortization		0		0		0	1
Operating Expenses		(98)		(101)		(190)	(204)
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		(154)				(154)		(40)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member] | Revision of Prior Period, Adjustment [Member]
Segment Reporting Information [Line Items]
Income (Loss) before income taxes				108			227
Assets								5,700
Exelon Generation Co L L C [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		113		159		423	240
Revenues		3,880		4,210		8,613	9,506
Depreciation and Amortization		300		409		604	814
Operating Expenses		3,547		4,096		7,947	9,059
Interest expense, net		87		116		197	227
Income (Loss) before income taxes		860		202		313	854
Income taxes		329		78		(59)	301
Net income (loss)		529		118		368	540
Capital expenditures		372		383		930	890
Assets		47,003				47,003		48,995
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		271		252		601	568
Commonwealth Edison Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0		0		0	0
Revenues		1,417		1,351		2,856	2,759
Depreciation and Amortization		274		257		547	508
Operating Expenses		1,345		1,040		2,497	2,174
Interest expense, net		98		89		192	178
Income (Loss) before income taxes		(15)		232		189	429
Income taxes		46		46		82	85
Net income (loss)		(61)		186		107	344
Capital expenditures		523		459		1,029	961
Assets		33,896				33,896		32,765
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		11		5		16	9
PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0		0		0	0
Revenues		681		655		1,493	1,554
Depreciation and Amortization		88		83		173	164
Operating Expenses		618		510		1,242	1,187
Interest expense, net		36		33		71	67
Income (Loss) before income taxes		32		115		187	307
Income taxes		(7)		13		9	37
Net income (loss)		39		102		178	270
Capital expenditures		253		225		512	447
Assets		12,120				12,120		11,469
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		2		2		4	3
Baltimore Gas and Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0		0		0	0
Revenues		616		649		1,554	1,625
Depreciation and Amortization		129		117		272	252
Operating Expenses		573		569		1,263	1,325
Interest expense, net		32		29		64	58
Income (Loss) before income taxes		17		56		237	253
Income taxes		(22)		11		18	47
Net income (loss)		39		45		219	206
Capital expenditures		265		284		548	542
Assets		11,027				11,027		10,634
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		4		6		10	12
Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0		0		0	0
Revenues		1,016		1,091		2,187	2,319
Depreciation and Amortization		191		188		385	369
Operating Expenses		956		926		1,955	1,981
Interest expense, net		67		67		134	131
Income (Loss) before income taxes		7		112		126	234
Income taxes		(87)		6		(76)	11
Net income (loss)		94		106		202	223
Capital expenditures		310		340		686	698
Assets		23,004				23,004		22,719
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		3		3		7	7
Potomac Electric Power Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues		494		531		1,039	1,106
Depreciation and Amortization		92		93		186	186
Operating Expenses		436		438		899	929
Interest expense, net		34		34		68	68
Income (Loss) before income taxes		33		66		90	123
Income taxes		(24)		2		(19)	4
Net income (loss)		57		64		109	119
Capital expenditures		144		154		324	298
Assets		8,869				8,869		8,661
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		1		1		3	3
Delmarva Power and Light Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues		267		287		617	667
Depreciation and Amortization		47		45		94	91
Operating Expenses		263		243		547	550
Interest expense, net		15		15		31	30
Income (Loss) before income taxes		(9)		34		44	94
Income taxes		(28)		4		(20)	11
Net income (loss)		19		30		64	83
Capital expenditures		89		82		184	160
Assets		4,966				4,966		4,830
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		2		2		4	3
Atlantic City Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues		256		274		532	547
Depreciation and Amortization		44		40		86	71
Operating Expenses		258		246		509	498
Interest expense, net		15		15		29	28
Income (Loss) before income taxes		(15)		14		(1)	25
Income taxes		(33)		0		(32)	1
Net income (loss)		18		14		31	24
Capital expenditures		77		99		178	227
Assets		4,089				4,089		3,933
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		1		1		1	1
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues		0		0		0	0
Revenues		472		484		953	940
Depreciation and Amortization		19		25		42	47
Operating Expenses		478		484		958	942
Interest expense, net		107		75		179	152
Income (Loss) before income taxes		(108)		(73)		(175)	(151)
Income taxes		(40)		(10)		(49)	(27)
Net income (loss)		(67)		(63)		(126)	(123)
Capital expenditures		34		11		68	34
Assets		9,288				9,288		8,484
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		97		97		189	205
Depreciation and Amortization		8		10		19	20
Operating Expenses		97		100		190	208
Interest expense, net		3		3		6	5
Income (Loss) before income taxes		(2)		(2)		(7)	(8)
Income taxes		(2)		0		(5)	(5)
Net income (loss)		0		(2)		(2)	(3)
Capital expenditures		0		5		0	13
Assets		5,234				5,234		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				108			227
Assets								$ 5,700
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		470		482		949	935
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties		97		98		189	205
Electricity, Generation [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		3,146		3,468		6,571	7,487
Electricity, Generation [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(268)		(250)		(594)	(565)
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		3,414		3,718		7,165	8,052
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		353		333		1,022	1,213
Oil and Gas, Purchased [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		0		0		(3)	(1)
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		353		333		1,025	1,214
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		3,475		3,512		7,222	7,343
Electricity, US Regulated | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		1,047		1,067		2,133	2,205
Electricity, US Regulated | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(15)		(8)		(27)	(17)
Electricity, US Regulated | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(4)		(3)		(8)	(7)
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		1,417		1,351		2,856	2,759
Electricity, US Regulated | PECO Energy Co [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		586		566		1,189	1,185
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		504		540		1,118	1,198
Electricity, US Regulated | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		983		1,063		2,086	2,218
Electricity, US Regulated | Potomac Electric Power Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		494		531		1,039	1,106
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		237		261		523	572
Electricity, US Regulated | Atlantic City Electric Company [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		256		274		532	547
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	0
Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		236		218		832	883
Natural Gas, US Regulated | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		30		24		94	95
Natural Gas, US Regulated | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(1)		(4)		(2)	(8)
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		95		89		304	369
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		112		109		436	427
Natural Gas, US Regulated | Pepco Holdings LLC [Member] | Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		30		24		94	95
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		30		24		94	95
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		0		0		1	2
Service, Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(475)		(488)		(959)	(944)
Service, Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax		(94)		(95)		(182)	(199)
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		3		4		7	6
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		2		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		472		484		953	940
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		$ 97		$ 97		$ 189	$ 205

[1] Exelon’s consolidated assets include $9,937 million and $9,532 million at June 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 $3,542 million and $3,473 million at June 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 $9,916 million and $9,512 million at June 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 $3,505 million and $3,429 million at June 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 $21 million and $20 million at June 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 $37 million and $44 million at June 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.