Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net	Noncontrolling Interest [Member]	Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member] Membership Interest [Member]	Exelon Generation Co L L C [Member] Undistributed Earnings [Member]	Exelon Generation Co L L C [Member] Accumulated Other Comprehensive Income (Loss), net	Exelon Generation Co L L C [Member] Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member] Other Comprehensive Income (Loss) [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member] Common Stock [Member]	Commonwealth Edison Co [Member] Retained Earnings [Member]	Commonwealth Edison Co [Member] Other Additional Capital [Member]	Commonwealth Edison Co [Member] Retained Earnings, Unappropriated [Member]	Commonwealth Edison Co [Member] Retained Earnings Appropriated [Member]	PECO Energy Co [Member]	PECO Energy Co [Member] Common Stock [Member]	PECO Energy Co [Member] Retained Earnings [Member]	PECO Energy Co [Member] Accumulated Other Comprehensive Income (Loss), net	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member] Common Stock [Member]	Baltimore Gas and Electric Company [Member] Retained Earnings [Member]	Baltimore Gas and Electric Company [Member] Membership Interest [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member] Membership Interest [Member]	Pepco Holdings LLC [Member] Undistributed Earnings [Member]	Potomac Electric Power Company [Member]	Potomac Electric Power Company [Member] Common Stock [Member]	Potomac Electric Power Company [Member] Retained Earnings [Member]	Delmarva Power & Light Company [Member]	Delmarva Power & Light Company [Member] Common Stock [Member]	Delmarva Power & Light Company [Member] Retained Earnings [Member]	Atlantic City Electric Company [Member]	Atlantic City Electric Company [Member] Common Stock [Member]	Atlantic City Electric Company [Member] Retained Earnings [Member]
Beginning Balance (in shares) at Dec. 31, 2017	965,168
Beginning Balance at Dec. 31, 2017	$ 32,169	$ 18,964	$ (123)	$ 14,063	$ (3,026)	$ 2,291
Beginning Balance at Dec. 31, 2017								$ 15,959	$ 9,357	$ 4,349	$ (37)	$ 2,290																$ 8,807	$ 8,835	$ (28)
Beginning Balance at Dec. 31, 2017														$ 9,542	$ 1,588		$ 6,822	$ (1,639)	$ 2,771	$ 3,577	$ 2,489	$ 1,087	$ 1		$ 1,605	$ 1,536	$ 3,141				$ 2,515	$ 1,470	$ 1,045	$ 1,335	$ 764	$ 571	$ 1,043	$ 912	$ 131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 2,079			2,005		74		443		370		73		664				664		460		460		$ 313		313	313	393		393	205		205	120		120	75		75
Long-Term Incentive Plan Activity (shares)	3,534
Long-Term Incentive Plan Activity	$ 41	41	0	0	0	0
Employee stock purchase plan issuances, shares	1,318
Employee stock purchase plan issuances	$ 105	105	0	0	0	0
Sale of noncontrolling interests	6	6				0		6	6			0
Changes in equity of noncontrolling interests	$ (60)					(60)		(60)				(60)
Common Stock, Dividends, Per Share, Declared	$ 1.38
Common stock dividends	$ (1,339)			(1,339)										(459)					(459)	(306)		(306)				(209)	(209)				(169)		(169)	(96)		(96)	(59)		(59)
Other Comprehensive Income (Loss), Net of Tax	42				41	1	$ 42	3			2	1
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	4			14	(10)			3		6	(3)									0		1	(1)
Distributions to member								(1,001)		(1,001)																		(326)		(326)
Contributions from parent	$ 0							155	155					500			500			89	89		0		109		109	385	385		166	166		150	150		67	67
Ending Balance (in shares) at Dec. 31, 2018	970,020
Ending Balance at Dec. 31, 2018	$ 33,047	19,116	(123)	14,743	(2,995)	2,306
Ending Balance at Dec. 31, 2018														10,247	1,588		7,322	(1,639)	2,976	3,820	2,578	1,242	0		1,714	1,640	3,354				2,717	1,636	1,081	1,509	914	595	1,126	979	147
Ending Balance at Dec. 31, 2018								15,508	9,518	3,724	(38)	2,304																9,259	9,220	39
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings appropriated																$ 0		(664)	664
Net income (loss)	$ 3,028			2,936		92		1,217		1,125		92		688				688		528		528		360		360	360	477		477	243		243	147		147	99		99
Long-Term Incentive Plan Activity (shares)	3,111
Long-Term Incentive Plan Activity	$ 40	40	0	0	0	0
Employee stock purchase plan issuances, shares	1,285
Employee stock purchase plan issuances	$ 112	112	0	0	0	0
Sale of noncontrolling interests	6	6				0		7	7			0
Changes in equity of noncontrolling interests	$ (48)					(48)		(48)				(48)
Common Stock, Dividends, Per Share, Declared	$ 1.45
Common stock dividends	$ (1,412)			(1,412)										(508)					(508)	(358)		(358)				(224)	(224)				(213)		(213)	(139)		(139)	(124)		(124)
Other Comprehensive Income (Loss), Net of Tax	(198)				(199)	(1)	(200)	7			6	(2)	$ 4
Distributions to member								(899)		(899)																		(526)		(526)
Contributions from parent	$ 0							41	41					250			250			188	188		0		193		193	398	398		160	160		63	63		175	175
Ending Balance (in shares) at Dec. 31, 2019	974,416
Ending Balance at Dec. 31, 2019	$ 34,573	19,274	(123)	16,267	(3,194)	2,349
Ending Balance at Dec. 31, 2019	32,224													10,677	1,588		7,572	(1,639)	3,156	4,178	2,766	1,412	0	3,683	1,907	1,776	3,683				2,907	1,796	1,111	1,580	977	603	1,276	1,154	122
Ending Balance at Dec. 31, 2019								15,830	9,566	3,950	(32)	2,346																9,608	9,618	(10)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings appropriated														3,156		0		(688)	688
Net income (loss)	$ 1,954			1,963		(9)		579		589		(10)		438				438		447		447		349		349	349	495		495	266		266	125		125	112		112
Long-Term Incentive Plan Activity (shares)	1,570
Long-Term Incentive Plan Activity	$ 40	40	0	0	0	0
Employee stock purchase plan issuances, shares	1,480
Employee stock purchase plan issuances	$ 56	56	0	0	0	0
Sale of noncontrolling interests	3	3				0		3	3			0
Changes in equity of noncontrolling interests	$ (57)	0				(57)		(59)				(59)
Distribution to member of deferred taxes associated with net retirement benefit obligation								(9)	(9)
Common Stock, Dividends, Per Share, Declared	$ 1.53
Common stock dividends	$ (1,495)			(1,495)										(499)					(499)	(340)		(340)				(246)	(246)				(232)		(232)	(141)		(141)	(114)		(114)
Other Comprehensive Income (Loss), Net of Tax	$ (206)				(206)	0	$ (206)	2			2	0	$ 2
Distributions to member								(1,734)		(1,734)																		(553)		(553)
Contributions from parent								64	64					713			713			248	248		0		411	0	411	494	494		262	262		112	112		117	117
Ending Balance (in shares) at Dec. 31, 2020	977,466
Ending Balance at Dec. 31, 2020	$ 34,868	$ 19,373	$ (123)	$ 16,735	$ (3,400)	$ 2,283
Ending Balance at Dec. 31, 2020	$ 32,585													11,329	$ 1,588		$ 8,285	(1,639)	3,095	$ 4,533	$ 3,014	$ 1,519	$ 0	$ 4,197	$ 2,318	$ 1,879	$ 4,197				$ 3,203	$ 2,058	$ 1,145	$ 1,676	$ 1,089	$ 587	$ 1,391	$ 1,271	$ 120
Ending Balance at Dec. 31, 2020								$ 14,676	$ 9,624	$ 2,805	$ (30)	$ 2,277																$ 10,044	$ 10,112	$ (68)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings appropriated														$ 3,095		$ 0		$ (438)	$ 438