Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Undistributed 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, 2016	958,778
Beginning Balance at Dec. 31, 2016	$ 27,629	$ 18,794	$ (2,327)	$ 12,042		$ (2,660)	$ 1,780
Beginning Balance at Dec. 31, 2016									$ 13,284	$ 9,261	$ 2,298	$ (54)	$ 1,779																$ 8,005	$ 8,077	$ (72)
Beginning Balance at Dec. 31, 2016															$ 8,725	$ 1,588		$ 6,150	$ (1,639)	$ 2,626	$ 3,415	$ 2,473	$ 941	$ 1		$ 1,421	$ 1,427	$ 2,848				$ 2,289	$ 1,309	$ 980	$ 1,326	$ 764	$ 562	$ 1,034	$ 912	$ 122
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 3,869			3,779			90		2,798		2,710		88		567				567		434		434		$ 307		307	307	355		355	198		198	121		121	77		77
Long-Term Incentive Plan Activity (shares)	5,066
Long-Term Incentive Plan Activity	$ 56	56	0	0		0	0
Employee stock purchase plan issuances, shares	1,324
Employee stock purchase plan issuances	$ 150	150	0	0		0	0
Stock Issued During Period, Value, Treasury Stock Reissued	1,150		2,204	(1,054)
Sale of noncontrolling interests	407	(36)					443		407	(36)			443
Changes in equity of noncontrolling interests	(20)						(20)		(18)				(18)
Common stock dividends	(1,243)			(1,243)											(422)					(422)	(288)		(288)				(198)	(198)				(133)		(133)	(112)		(112)	(68)		(68)
Other Comprehensive Income (Loss), Net of Tax	171					173	(2)		15			17	(2)
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	0			539		(539)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid									33	33
Distributions to member									(659)		(659)																		(311)		(311)
Contributions from parent	$ 0								99	99					651			651								184		184	758	758		161	161
Income Tax Effects Allocated Directly to Equity, Other																					16	16		0
Ending Balance (in shares) at Dec. 31, 2017	965,168
Ending Balance at Dec. 31, 2017	$ 32,169	18,964	(123)	14,063		(3,026)	2,291
Ending 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
Ending Balance at Dec. 31, 2017									15,959	9,357	4,349	(37)	2,290																8,807	8,835	(28)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated																	$ 0		(567)	567
Other Additional Capital															21			21
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	(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		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								109		109	385	385		166	166		150	150		67	67
Income Tax Effects Allocated Directly to Equity, Other	$ 0																				89	89
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	30,741														10,247	1,588		7,322	(1,639)	2,976	3,820	2,578	1,242	0	3,354	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															2,976		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)	0					(48)		(48)				(48)
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				193	0	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