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		$ 971							$ 399						$ 141					$ 127					$ 125			$ 140			$ 58			$ 57			$ 28
Other Comprehensive Income (Loss), Net of Tax		$ (12)				(10)	[1]		11			13	[1]										0	[1]
Ending balance at Mar. 31, 2017	[1]					(2,670)
Ending Balance at Mar. 31, 2017	[1]											(41)
Ending Balance at Mar. 31, 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		$ 636			585			51	186		136	0		50	165			165		113	0	113	0		128		128	65	0	65	31		31	31		31	7		7
Stock Issued During Period, Shares, Share-based Compensation, Gross		1,685
Stock Issued During Period, Value, Share-based Compensation, Gross		$ (3)	(3)	0	0	0		0
Stock Issued During Period, Shares, Employee Stock Purchase Plans		361
Stock Issued During Period, Value, Employee Stock Purchase Plan		$ 12	12	0	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(9)						(9)	(9)					(9)
Common stock dividends		(334)			(334)										(114)				(114)	(287)	0	(287)	0		(52)		(52)				(25)		(25)	(36)		(36)	(9)		(9)
Other Comprehensive Income (Loss), Net of Tax		72				71	[1]	1	7		0	6	[1]	1									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									(188)		(188)																	(71)	0	(71)
Adjustments to Additional Paid in Capital, Other															113		113
Ending Balance (in shares) at Mar. 31, 2018		967,214
Ending balance at Mar. 31, 2018		$ 32,565	$ 18,973	$ (123)	$ 14,346	$ (2,965)	[1]	$ 2,334
Ending Balance at Mar. 31, 2018									$ 15,958	$ 9,357	$ 4,303	$ (34)	[1]	$ 2,332														$ 8,819	$ 8,835	$ (16)
Ending Balance at Mar. 31, 2018		$ 30,231													9,706	$ 1,588	$ 6,935	(1,639)	2,822	$ 3,403	$ 2,489	$ 914	$ 0	[1]	$ 3,217	$ 1,605	$ 1,612				$ 2,539	$ 1,470	$ 1,069	$ 1,330	$ 764	$ 566	$ 1,041	$ 912	$ 129
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															$ (2,822)			$ (165)	$ (165)

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