Consolidated Statements of Changes in Shareholders Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member] Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member] Membership Interest [Member]	Exelon Generation Co L L C [Member] Retained Earnings, Unappropriated [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member] Common Stock [Member]	Commonwealth Edison Co [Member] Retained Earnings [Member]	Commonwealth Edison Co [Member] Retained Earnings, Unappropriated [Member]	Commonwealth Edison Co [Member] Other Paid-in-Capital [Member]	Commonwealth Edison Co [Member] Retained Earnings, Appropriated	PECO Energy Co [Member]	PECO Energy Co [Member] Common Stock [Member]	PECO Energy Co [Member] Retained Earnings [Member]	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member] Common Stock [Member]	Baltimore Gas and Electric Company [Member] Retained Earnings [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member] Membership Interest [Member]	Pepco Holdings LLC [Member] Retained Earnings, Unappropriated [Member]	Potomac Electric Power Company [Member]	Potomac Electric Power Company [Member] Common Stock [Member]	Potomac Electric Power Company [Member] Retained Earnings [Member]	Delmarva Power and Light Company [Member]	Delmarva Power and Light Company [Member] Common Stock [Member]	Delmarva Power and 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, 2019	974,416
Beginning balance at Dec. 31, 2019	$ 34,573	$ 19,274	$ (123)	$ 16,267	$ (3,194)	$ 2,349
Beginning Balance at Dec. 31, 2019							$ 15,830	$ (32)	$ 2,346	$ 9,566	$ 3,950													$ 9,608	$ 9,618	$ (10)
Beginning Balance at Dec. 31, 2019												$ 10,677	$ 1,588		$ (1,639)	$ 7,572	$ 3,156	$ 4,178	$ 2,766	$ 1,412	$ 3,683	$ 1,907	$ 1,776				$ 2,907	$ 1,796	$ 1,111	$ 1,580	$ 977	$ 603	$ 1,276	$ 1,154	$ 122
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 376			582		(206)	(161)		(206)		45	168			168			140		140	181		181	108		108	52		52	45		45	13		13
Long -Term Incentive Plan Activity (shares)	1,354
Lont-Term Incentive Plan Activity	$ (4)	(4)
Employee stock purchase plan issuances (shares)	470
Employee stock purchase plan issuances	$ 31	31
Changes in equity of noncontrolling interests	(9)					(9)	(11)		(11)
Sale of noncontrolling interests	2	2					2			2
Common stock dividends	(374)			(374)								(125)					(125)	(85)		(85)	(62)		(62)				(28)		(28)	(52)		(52)	(23)		(23)
Distributions to member							(468)				(468)													(134)		(134)
Contributions from parent												125				125		231	231					144	144		137	137		6	6		1	1
Other comprehensive income (loss), net of income taxes	$ 21				21		(9)	(9)	0		0
Ending balance (in shares) at Mar. 31, 2020	976,240
Ending balance at Mar. 31, 2020	$ 34,616	19,303	(123)	16,475	(3,173)	2,134
Ending Balance at Mar. 31, 2020							15,183	(41)	2,129	9,568	3,527													9,726	9,762	(36)
Ending Balance at Mar. 31, 2020												10,845	1,588		(1,639)	7,697	3,199	4,464	2,997	1,467	3,802	1,907	1,895				3,068	1,933	1,135	1,579	983	596	1,267	1,155	112
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.38
Appropriation of retained earnings for future dividends														$ 0	(168)		168
Appropriation of retained earnings for future dividends												3,095
Beginning balance (in shares) at Dec. 31, 2020	977,466
Beginning balance at Dec. 31, 2020	$ 34,868	19,373	(123)	16,735	(3,400)	2,283
Beginning Balance at Dec. 31, 2020							14,676	(30)	2,277	9,624	2,805													10,044	10,112	(68)
Beginning Balance at Dec. 31, 2020	32,585											11,329	1,588		(1,639)	8,285	3,095	4,533	3,014	1,519	4,197	2,318	1,879				3,203	2,058	1,145	1,676	1,089	587	1,391	1,271	120
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ (264)			(289)		25	(769)		24		(793)	197			197			167		167	209		209	128		128	59		59	56		56	14		14
Long -Term Incentive Plan Activity (shares)	640
Lont-Term Incentive Plan Activity	$ 5	5
Employee stock purchase plan issuances (shares)	902
Employee stock purchase plan issuances	$ 34	34
Changes in equity of noncontrolling interests	(10)					(10)	(10)		(10)
Common stock dividends	(374)			(374)								(127)					(127)	(85)		(85)	(74)		(74)				(28)		(28)	(40)		(40)	(14)		(14)
Distributions to member							(458)				(458)													(81)		(81)
Contributions from parent												198				198								560	560		138	138		120	120		303	303
Other comprehensive income (loss), net of income taxes	$ 54				54		1	1	0		0
Ending balance (in shares) at Mar. 31, 2021	979,008
Ending balance at Mar. 31, 2021	$ 34,313	$ 19,412	$ (123)	$ 16,072	$ (3,346)	$ 2,298
Ending Balance at Mar. 31, 2021							$ 13,440	$ (29)	$ 2,291	$ 9,624	$ 1,554													$ 10,651	$ 10,672	$ (21)
Ending Balance at Mar. 31, 2021	$ 32,015											11,597	$ 1,588		(1,639)	$ 8,483	3,165	$ 4,615	$ 3,014	$ 1,601	$ 4,332	$ 2,318	$ 2,014				$ 3,372	$ 2,196	$ 1,176	$ 1,812	$ 1,209	$ 603	$ 1,694	$ 1,574	$ 120
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.38
Appropriation of retained earnings for future dividends												$ 3,165		$ 0	$ (197)		$ 197