Consolidated Statement 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] Membership Interest [Member]	Exelon Generation Co L L C [Member] Retained Earnings, Unappropriated [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 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) [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 at Dec. 31, 2016	[1]					$ (2,660)
Beginning Balance at Dec. 31, 2016	[1]											$ (54)
Beginning Balance at Dec. 31, 2016	[1]																						$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 1,928							$ 508						$ 447					$ 327					$ 231			$ 359			$ 188			$ 107			$ 77
Other Comprehensive Income (Loss), Net of Tax		$ 69				71	[1]		16			18	[1]										0	[1]
Ending balance at Sep. 30, 2017	[1]					(2,589)
Ending Balance at Sep. 30, 2017	[1]											(36)
Ending Balance at Sep. 30, 2017	[1]																						1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															(2,771)
Beginning Balance (in shares) at Dec. 31, 2017		965,168
Beginning balance at Dec. 31, 2017		$ 32,187	$ 18,964	$ (123)	$ 14,081	(3,026)	[1]	$ 2,291
Beginning Balance at Dec. 31, 2017									15,959	$ 9,357	$ 4,349	(37)	[1]	$ 2,290														8,825	$ 8,835	$ (10)
Beginning Balance at Dec. 31, 2017		29,896													9,542	$ 1,588	$ 6,822	$ (1,639)	$ 2,771	3,577	$ 2,489	$ 1,087	1	[1]	3,141	$ 1,605	$ 1,536				2,533	$ 1,470	$ 1,063	1,335	$ 764	$ 571	1,043	$ 912	$ 131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 1,979			1,858			121	667		547	0		120	523			523		336	0	336	0		242	0	242	336		336	174		174	90		90	76		76
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,677
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 32	32	0	0	0		0
Stock Issued During Period, Shares, Employee Stock Purchase Plans		997
Stock Issued During Period, Value, Employee Stock Purchase Plan		$ 67	67	0	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(46)						(46)	(46)					(46)
Common stock dividends		(1,004)			(1,004)										(345)				(345)	(300)	0	(300)	0		(157)	0	(157)				(128)		(128)	(58)		(58)	(46)		(46)
Equity Contribution																				71	71
Other Comprehensive Income (Loss), Net of Tax		169				167	[1]	2	11		0	9	[1]	2									0	[1]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		$ 4			14	(10)			3		6	(3)								0		1	(1)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared									(688)		(688)																	(232)		(232)
Adjustments to Additional Paid in Capital, Other									54	54					387		387								18	18	0	237	237		85	85		150	150
Ending Balance (in shares) at Sep. 30, 2018		968,842
Ending balance at Sep. 30, 2018		$ 33,388	$ 19,063	$ (123)	$ 14,949	$ (2,869)	[1]	$ 2,368
Ending Balance at Sep. 30, 2018									$ 15,960	$ 9,411	$ 4,214	$ (31)	[1]	$ 2,366														$ 9,166	$ 9,072	$ 94
Ending Balance at Sep. 30, 2018		$ 31,020													10,107	$ 1,588	$ 7,209	(1,639)	2,949	$ 3,684	$ 2,560	$ 1,124	$ 0	[1]	$ 3,244	$ 1,623	$ 1,621				$ 2,664	$ 1,555	$ 1,109	$ 1,517	$ 914	$ 603	$ 1,073	$ 912	$ 161
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															$ (2,949)			$ (523)	$ (523)

[1] All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.