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]	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] Retained Earnings, Unappropriated/Undistributed [Member]	Exelon Generation Co L L C [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member] Noncontrolling Interest [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member] Common Stock [Member]	Commonwealth Edison Co [Member] Other Paid-in-Capital [Member]	Commonwealth Edison Co [Member] Retained Earnings, Unappropriated/Undistributed [Member]	Commonwealth Edison Co [Member] Retained Earnings, Appropriated	Commonwealth Edison Co [Member] Retained Earnings [Member]	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/Undistributed [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, 2018	970,020
Beginning balance at Dec. 31, 2018	$ 33,070	$ 19,116	$ (123)	$ 14,766	$ (2,995)	$ 2,306
Beginning Balance at Dec. 31, 2018								$ 15,508	$ 9,518	$ 3,724	$ (38)	$ 2,304													$ 9,282	$ 9,220	$ 62
Beginning Balance at Dec. 31, 2018													$ 10,247	$ 1,588	$ 7,322	$ (1,639)	$ 2,976		$ 3,820	$ 2,578	$ 1,242	$ 3,354	$ 1,714	$ 1,640				$ 2,740	$ 1,636	$ 1,104	$ 1,509	$ 914	$ 595	$ 1,126	$ 979	$ 147
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 966			907		59		422		363		59	157			157			168		168	160		160	117		117	55		55	53		53	10		10
Stock issued during period, shares, long-term incentive plan activity	2,446
Stock issued during period, value, long-term incentive plan activity	$ (3)	(3)	0	0	0	0
Stock issued during period, shares, employee stock purchase plan	320
Stock issued during period, value, employee stock purchase plan	$ 51	51	0	0	0	0
Changes in equity of noncontrolling interests	(17)					(17)		(17)				(17)
Sale of noncontrolling interests	7	7						7	7
Common stock dividends	(352)			(352)									(127)				(127)		(90)		(90)	(56)		(56)				(24)		(24)	(41)		(41)	(12)		(12)
Distributions to member								(225)		(225)															(128)		(128)
Contributions from parent													63		63				145	145					19	19		14	14					5	5
Other comprehensive income (loss), net of income taxes	$ (18)				(17)	(1)	$ (18)	1		0	2	(1)
Ending balance (in shares) at Mar. 31, 2019	972,786
Ending balance at Mar. 31, 2019	$ 33,704	19,171	(123)	15,321	(3,012)	2,347
Ending Balance at Mar. 31, 2019								15,696	9,525	3,862	(36)	2,345													9,290	9,239	51
Ending Balance at Mar. 31, 2019													10,340	1,588	7,385	(1,639)	3,006		4,043	2,723	1,320	3,458	1,714	1,744				2,785	1,650	1,135	1,521	914	607	1,129	984	145
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Appropriation of retained earnings for future dividends																(157)	157	$ 0
Appropriation of retained earnings for future dividends													3,156
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	9,566	3,950	(32)	2,346													9,608	9,618	(10)
Beginning Balance at Dec. 31, 2019	32,224												10,677	1,588	7,572	(1,639)	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)		45		(206)	168			168			140		140	181		181	108		108	52		52	45		45	13		13
Stock issued during period, shares, long-term incentive plan activity	1,354
Stock issued during period, value, long-term incentive plan activity	$ (4)	(4)	0	0	0	0
Stock issued during period, shares, employee stock purchase plan	470
Stock issued during period, value, employee stock purchase plan	$ 31	31	0	0	0	0
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		$ 21	(9)		0	(9)	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	$ 9,568	$ 3,527	$ (41)	$ 2,129													$ 9,726	$ 9,762	$ (36)
Ending Balance at Mar. 31, 2020	$ 32,482												10,845	$ 1,588	$ 7,697	(1,639)	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]
Appropriation of retained earnings for future dividends													$ 3,199			$ (168)	$ 168	$ 0