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] Undistributed Earnings [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]	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] Undistributed Earnings [Member]	Pepco Holdings LLC [Member] Membership Interest [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, 2015	[1]					$ (2,624)					$ (63)												$ 1
Beginning balance at Dec. 31, 2015	[1]					(2,624)					(63)												1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 956							$ 556						$ 297					$ 346					$ 191						$ 20			$ (16)			$ (50)
Other Comprehensive Income (Loss), Net of Tax		$ 96				101	[1]		2		7	[1]											0	[1]
Ending balance at Sep. 30, 2016	[1]					(2,523)					(56)												1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from Contributions from Affiliates									142
Net income | Successor [Member]																												$ (91)
Other Comprehensive Income (Loss), Net of Tax | Successor [Member]																												0
Ending balance at Sep. 30, 2016	[1]					(2,523)					(56)												1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from Contributions from Affiliates | Successor [Member]																												1,088
Retained Earnings, Appropriated															(2,626)
Beginning Balance (in shares) at Dec. 31, 2016		958,778
Beginning balance at Dec. 31, 2016		$ 27,612	$ 18,794	$ (2,327)	$ 12,030	(2,660)	[1]	$ 1,775			(54)	[1]											1	[1]
Beginning Balance at Dec. 31, 2016		25,837													8,725	$ 1,588	$ 6,150	$ (1,639)	$ 2,626	3,415	$ 2,473	$ 941	1		2,848	$ 1,421	$ 1,427				2,300	$ 1,309	$ 991	1,326	$ 764	$ 562	1,034	$ 912	$ 122
Beginning Balance (Successor [Member]) at Dec. 31, 2016																												8,016	$ (61)	$ 8,077
Beginning Balance at Dec. 31, 2016									13,256	$ 2,275	(54)		$ 1,774	$ 9,261
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income | Successor [Member]																												359	359
Net income		1,911	0	0	1,899	0		12	491	479	0		12		447			447		327		327			231		231				188	0	188	107		107	77		77
Stock Issued During Period, Value, Treasury Stock Reissued		$ 1,150		2,204	(1,054)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid									33					33
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,911
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 43	43	0	0	0		0
Stock Issued During Period, Shares, Employee Stock Purchase Plans		996
Stock Issued During Period, Value, Employee Stock Purchase Plan		$ 61	61	0	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(11)						(11)	(11)				(11)
Noncontrolling Interest, Increase from Sale of Parent Equity Interest		407	(36)					443	407				443	(36)
Income Tax Effects Allocated Directly to Equity, Other | Successor [Member]																												7		7
Income Tax Effects Allocated Directly to Equity, Other									99					99						(16)
Common stock dividends		(925)	0	0	(925)	0		0												(216)	0	(216)	0		(148)		(148)				(133)	0	(133)	(82)		(82)	(53)		(53)
Other Comprehensive Income (Loss), Net of Tax | Successor [Member]																												0
Other Comprehensive Income (Loss), Net of Tax		69	0	0	0	71	[1]	(2)	16	0	18	[1]	(2)										0	[1]
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]																												(267)	(267)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared									(494)	(494)
Employee stock purchase plan issuances		$ 61	61	0	0	0		0
Dividends															(316)				(316)
Adjustments to Additional Paid in Capital, Other | Successor [Member]																												751		751
Adjustments to Additional Paid in Capital, Other															567		567								77	77	0				161	161
Ending Balance (in shares) at Sep. 30, 2017		962,685
Ending balance at Sep. 30, 2017		$ 30,317	$ 18,862	$ (123)	$ 11,950	$ (2,589)	[1]	$ 2,217			(36)	[1]											1	[1]
Ending Balance at Sep. 30, 2017		$ 28,100													9,444	$ 1,588	6,738	(1,639)	2,757	$ 3,542	$ 2,489	$ 1,052	$ 1		$ 3,008	$ 1,498	$ 1,510				$ 2,516	$ 1,470	$ 1,046	$ 1,351	$ 764	$ 587	$ 1,058	$ 912	$ 146
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from Contributions from Affiliates | Successor [Member]																												758
Proceeds from Contributions from Affiliates									102
Ending Balance (Successor [Member]) at Sep. 30, 2017																												$ 8,866	$ 31	$ 8,835
Ending Balance at Sep. 30, 2017									$ 13,797	$ 2,260	$ (36)		$ 2,216	$ 9,357
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															(2,757)			$ (447)	$ (447)
Other Additional Capital															$ 21		$ 21

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