Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands, $ in Millions		Total	Pepco Holdings LLC [Member]	Commitments [Member] Pepco Holdings LLC [Member]	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]		Noncontrolling Interest [Member]	Preference Stock Not Subject To Mandatory Redemption [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) [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] Parent [Member]	Baltimore Gas and Electric Company [Member] Common Stock [Member]	Baltimore Gas and Electric Company [Member] Common Stock [Member] Parent [Member]	Baltimore Gas and Electric Company [Member] Retained Earnings [Member]	Baltimore Gas and Electric Company [Member] Membership Interest [Member]	Baltimore Gas and Electric Company [Member] Membership Interest [Member] Parent [Member]	Baltimore Gas and Electric Company [Member] Preference Stock Not Subject To Mandatory Redemption [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member] Pepco Holdings LLC [Member]	[4]	Pepco Holdings LLC [Member] Deferred Compensation, Share-based Payments [Member] Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member] Common Stock [Member]	[1]	Pepco Holdings LLC [Member] Retained Earnings [Member]	Pepco Holdings LLC [Member] Membership Interest [Member]	Pepco Holdings LLC [Member] Membership Interest [Member] Pepco Holdings LLC [Member]	[4]	Pepco Holdings LLC [Member] Undistributed Earnings [Member]	Pepco Holdings LLC [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Pepco Holdings LLC [Member] Additional Paid-in Capital [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]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 27,330			$ 18,676	$ (2,327)	$ 12,104	$ (2,624)		$ 1,308	$ 193
Other Additional Capital | Successor [Member]																																																$ 3,829
Beginning Balance (in shares) at Dec. 31, 2015		954,668
Beginning Balance at Dec. 31, 2015																		$ 8,243	$ 1,588	$ 5,677	$ (1,639)	$ 2,617	$ 3,236	$ 2,455	$ 780	$ 1		$ 2,877		$ 1,367		$ 1,320	$ 2,687		$ 190														$ 2,240	$ 1,122	$ 1,118	$ 1,237	$ 612	$ 625	$ 1,000	$ 773	$ 227
Beginning Balance (Predecessor [Member]) at Dec. 31, 2015																																				$ 4,413				$ 3,832		$ 617					$ (36)
Beginning Balance at Dec. 31, 2015												$ 12,978	$ 8,997	$ 2,737	$ (63)		$ 1,307
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) | Predecessor [Member]																																				19						19
Employee stock purchase plan issuances | Predecessor [Member]																																				3				3
Tax benefit on stock compensation | Predecessor [Member]																																				(1)
Other comprehensive income (loss), net of income taxes | Predecessor [Member]																																				1											1
Ending Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439				3,838		636					(35)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Predecessor [Member]																																				3				3
Beginning Balance (in shares) at Dec. 31, 2015		954,668
Beginning Balance at Dec. 31, 2015																		8,243	1,588	5,677	(1,639)	2,617	3,236	2,455	780	1		2,877		1,367		1,320	2,687		190														2,240	1,122	1,118	1,237	612	625	1,000	773	227
Beginning Balance (Predecessor [Member]) at Dec. 31, 2015																																				4,413				3,832		617					(36)
Beginning Balance at Dec. 31, 2015												12,978	8,997	2,737	(63)		1,307
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		$ 1,196	$ (66)				1,121			67	8	550		483			67	378			378		438		438			294				294	294																42		42	(9)		(9)	(42)	0	(42)
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,868
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 85			85	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,242
Employee stock purchase plan issuances		$ 55			55	0	0	0		0	0
Tax benefit on stock compensation		(18)			(18)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		5								5
Sale of noncontrolling interests		239			(4)					243		239	(4)				243
Noncontrolling Interest, Change in Redemption Value		157								157		157					157
Noncontrolling Interest, Period Increase (Decrease)												5					5
Common stock dividends		(1,172)					(1,172)											(369)				(369)	(277)		(277)			(179)				(179)	(179)																(169)		(169)	(54)		(54)	(63)	0	(63)
Preferred and preference stock dividends		(8)									(8)																	(8)				(8)	(8)
Stock Redeemed or Called During Period, Value		(193)									(193)																	(190)							(190)
Adjustments to Additional Paid in Capital, Other												268	268					315		315								61	$ (7)	61	$ (7)		61	$ (7)															187	187		152	152		139	139
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(922)		(922)
Income Tax Effects Allocated Directly to Equity, Other																							18	18		0
Other comprehensive income (loss), net of income taxes		$ (36)					0	(36)				9			9
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016																		8,725	1,588	6,150	(1,639)	2,626	3,415	2,473	941	1		2,848		1,421		1,427	2,848		0														2,300	1,309	991	1,326	764	562	1,034	912	122
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016							$ 8,077			$ (61)	0
Ending Balance at Dec. 31, 2016												13,284	9,261	2,298	(54)		1,779
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Additional Capital | Successor [Member]																																																3,835
Common stock | Successor [Member]																																																$ 3
Beginning Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439				$ 3,838		$ 636					(35)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) | Successor [Member]																																				(61)
Other comprehensive income (loss), net of income taxes | Successor [Member]																																				0
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016																		8,725	1,588	6,150	(1,639)	2,626	3,415	2,473	941	1		2,848		1,421		1,427	2,848		0														2,300	1,309	991	1,326	764	562	1,034	912	122
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016							8,077			(61)	0
Ending Balance at Dec. 31, 2016												13,284	9,261	2,298	(54)		1,779
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Successor [Member]				$ 33
Stockholders' Equity, Other																																							$ 29
Common stock | Successor [Member]																																				165
Business Combination, Contingent Consideration, Asset | Successor [Member]																																				235
Business Combination, Contingent Consideration, Asset		$ 235										163
Beginning Balance (Successor [Member]) at Mar. 24, 2016	[2]																																			7,200							7,200			0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) | Successor [Member]																																				(61)										(61)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid | Successor [Member]																																				53							53
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]	[3]																																			(400)							(400)
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions | Successor [Member]																																				1,251							1,251
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016																		8,725	1,588	6,150	(1,639)	2,626	3,415	2,473	941	1		2,848		1,421		1,427	2,848		0														2,300	1,309	991	1,326	764	562	1,034	912	122
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016							8,077			(61)	0
Ending Balance at Dec. 31, 2016												13,284	9,261	2,298	(54)		1,779
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Successor [Member]																																				35	$ (62)						35	$ (62)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 27,640			18,794	(2,327)	12,053	(2,660)	[5]	1,780	0				(54)	[5]										1	[5]
Other Additional Capital																		158		158
Retained Earnings, Appropriated																					(378)	378
Net income (loss)		$ 3,876	364				3,786			90	0	2,798		2,710			88	567			567		434		434			307				307	307			362										362			205		205	121		121	77	0	77
Stock Issued During Period, Shares, Share-based Compensation, Gross		5,066
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 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, Shares, New Issues		0
Stock Issued During Period, Value, New Issues		$ 0			0
Stock Issued During Period, Value, Treasury Stock Reissued		(1,150)				2,204	(1,054)
Tax benefit on stock compensation					0
Sale of noncontrolling interests		407			(36)					443		407	(36)				443
Noncontrolling Interest, Change in Redemption Value		(20)								(20)
Noncontrolling Interest, Period Increase (Decrease)												(18)					(18)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid												33	33
Common stock dividends		(1,243)					(1,243)											(422)				(422)	(288)		(288)			(198)				(198)	(198)																(133)		(133)	(112)		(112)	(68)	0	(68)
Adjustments to Additional Paid in Capital, Other		0										99	99					651		651								184		184			184		0														161	161
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(659)		(659)																						(311)										(311)
Income Tax Effects Allocated Directly to Equity, Other		0																					16	16
Other comprehensive income (loss), net of income taxes		$ 171					0	173	[5]	(2)		15			17	[5]	(2)									0	[5]									0
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions																																				758							758
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard							539	(539)
Ending Balance (in shares) at Dec. 31, 2017		965,168
Ending Balance at Dec. 31, 2017		$ 29,896																9,542	1,588	6,822	(1,639)	2,771	3,577	2,489	1,087	1		3,141		1,605		1,536	3,141		0														2,533	1,470	1,063	1,335	764	571	1,043	912	131
Ending Balance at Dec. 31, 2017												15,959	9,357	4,349	(37)		2,290																			8,825							8,835			(10)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		32,187			18,964	(123)	14,081	(3,026)	[5]	2,291	0				(37)	[5]										1	[5]
Other Additional Capital																		21		21
Retained Earnings, Appropriated																		2,771			(567)	567
Additional Paid in Capital																		6,822
Common stock		18,964																1,588					2,489					1,605																					1,470			764			912
Net income (loss)		$ 2,084	$ 453				2,010			74	0	443		370			73	664			664		460		460			313				313	313			398										398			210		210	120		120	75	0	75
Stock Issued During Period, Shares, Share-based Compensation, Gross		3,534
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 41			41	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,318
Employee stock purchase plan issuances		$ 105			105	0	0	0		0	0
Sale of noncontrolling interests		6			6			0		0	0	6	6	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(60)			0					(60)		(60)					(60)
Common stock dividends		(1,339)					(1,339)											(459)				(459)	(306)		(306)			(209)				(209)	(209)																(169)		(169)	(96)		(96)	(59)	0	(59)
Adjustments to Additional Paid in Capital, Other												155	155					500		500								109		109		0	109		0														166	166		150	150		67	67
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(1,001)		(1,001)																						(326)										(326)
Income Tax Effects Allocated Directly to Equity, Other		0																					89	89
Other comprehensive income (loss), net of income taxes		42					0	41	[5]	1		3			2	[5]	1									0	[5]									0
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions																																				385							385
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard		$ 4					14	(10)				3		6	(3)
Ending Balance (in shares) at Dec. 31, 2018		970,020
Ending Balance at Dec. 31, 2018		$ 30,764																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		$ 0														2,740	$ 1,636	$ 1,104	1,509	$ 914	$ 595	1,126	$ 979	$ 147
Ending Balance at Dec. 31, 2018												$ 15,508	$ 9,518	$ 3,724	(38)		$ 2,304																			$ 9,282							$ 9,220			$ 62	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		33,070			$ 19,116	$ (123)	$ 14,766	$ (2,995)	[5]	$ 2,306	$ 0				$ (38)	[5]										$ 0	[5]
Retained Earnings, Appropriated																		2,976			$ (664)	$ 664
Additional Paid in Capital																		7,322
Common stock		$ 19,116																$ 1,588					$ 2,578					$ 1,714																					$ 1,636			$ 914			$ 979

[1] At March 23, 2016 and December 31, 2015, PHI's (predecessor) shareholders' equity included $3,835 million and $3,829 million of other paid-in capital, and $3 million and $3 million of common stock, respectively.

[2] The March 24, 2016, beginning balance differs from the PHI Merger total purchase price by $59 million related to an acquisition accounting adjustment recorded at Exelon Corporate to reflect unitary state income tax consequences of the merger.

[3] Distribution to member includes $235 million of net assets associated with PHI's unregulated business interests and $165 million of cash, each of which were distributed by PHI to Exelon.

[4] he liabilities assumed include $29 million for PHI stock-based compensation awards and $33 million for a merger related obligation, each assumed by PHI from Exelon. See Note 5 — Mergers, Acquisitions and Dispositions.

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