Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands		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] 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] 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]	Pepco Holdings LLC [Member] Deferred Compensation, Share-based Payments [Member] Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member] Common Stock [Member]		Pepco Holdings LLC [Member] Retained Earnings [Member]	Pepco Holdings LLC [Member] Undistributed Earnings [Member]	Pepco Holdings LLC [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Pepco Holdings LLC [Member] Membership Interest [Member]	Pepco Holdings LLC [Member] Membership Interest [Member] Pepco Holdings LLC [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 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]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 24,133,000,000			$ 16,709,000,000	$ (2,327,000,000)	$ 10,910,000,000	$ (2,684,000,000)		$ 1,332,000,000	$ 193,000,000
Beginning Balance (in shares) at Dec. 31, 2014		894,568
Beginning Balance at Dec. 31, 2014																		$ 7,907,000,000	$ 1,588,000,000	$ 5,468,000,000	$ (1,639,000,000)	$ 2,490,000,000	$ 3,121,000,000	$ 2,439,000,000	$ 681,000,000	$ 1,000,000		$ 2,753,000,000		$ 1,360,000,000		$ 1,203,000,000	$ 2,563,000,000		$ 190,000,000												$ 2,087,000,000	$ 1,010,000,000	$ 1,077,000,000	$ 1,178,000,000	$ 537,000,000	$ 641,000,000	$ 877,000,000	$ 678,000,000	$ 199,000,000
Beginning Balance (Predecessor [Member]) at Dec. 31, 2014																																				$ 4,322,000,000			$ 3,803,000,000	[1]	$ 565,000,000		$ (46,000,000)
Beginning Balance at Dec. 31, 2014												$ 14,051,000,000	$ 3,803,000,000	$ (36,000,000)		$ 1,333,000,000	$ 8,951,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) | Predecessor [Member]																																				327,000,000					327,000,000
Net Income (Loss)		$ 2,250,000,000					2,269,000,000			(32,000,000)	13,000,000	1,340,000,000	1,372,000,000			(32,000,000)		426,000,000			426,000,000		378,000,000		378,000,000			288,000,000				288,000,000	288,000,000														187,000,000		187,000,000	76,000,000		76,000,000	40,000,000		40,000,000
Stock Issued During Period, Shares, Share-based Compensation, Gross		1,430
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 70,000,000			70,000,000	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,170
Employee stock purchase plan issuances | Predecessor [Member]																																				3,000,000			3,000,000
Employee stock purchase plan issuances		$ 32,000,000			32,000,000	0	0	0		0	0
Stock Issued During Period, Shares, New Issues		57,500
Stock Issued During Period, Value, New Issues		$ 1,868,000,000			1,868,000,000
Tax benefit on stock compensation | Predecessor [Member]																																				(5,000,000)
Tax benefit on stock compensation		(3,000,000)			(3,000,000)
Changes in equity of noncontrolling interests		4,000,000								4,000,000						0
Noncontrolling Interest, Change in Redemption Value		4,000,000								4,000,000		4,000,000				4,000,000
Noncontrolling interest acquired												1,000,000				(2,000,000)	1,000,000
Common stock dividends | Predecessor [Member]																																				(275,000,000)					(275,000,000)
Common stock dividends		(1,111,000,000)					(1,111,000,000)											(299,000,000)				(299,000,000)	(279,000,000)		(279,000,000)			(158,000,000)				(158,000,000)	(158,000,000)														(146,000,000)		(146,000,000)	(92,000,000)		(92,000,000)	(12,000,000)		(12,000,000)
Preferred and preference stock dividends		(13,000,000)									(13,000,000)																	(13,000,000)				(13,000,000)	(13,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(2,474,000,000)	(2,474,000,000)
Adjustments to Additional Paid in Capital, Other																		202,000,000		202,000,000								7,000,000		7,000,000			7,000,000														112,000,000	112,000,000		75,000,000	75,000,000		95,000,000	95,000,000
Income Tax Effects Allocated Directly to Equity, Other												47,000,000					47,000,000						16,000,000	16,000,000		0
Other comprehensive income (loss), net of income taxes | Predecessor [Member]																																				10,000,000							10,000,000
Other comprehensive income (loss), net of income taxes		$ 60,000,000						60,000,000				(27,000,000)		(27,000,000)
Distribution to member													0
Stock Issued During Period, Value, Dividend Reinvestment Plan | Predecessor [Member]																																				11,000,000			11,000,000
Ending Balance (in shares) at Dec. 31, 2015		954,668
Ending Balance at Dec. 31, 2015																		8,243,000,000	1,588,000,000	5,677,000,000	(1,639,000,000)	2,617,000,000	3,236,000,000	2,455,000,000	780,000,000	1,000,000		2,877,000,000		1,367,000,000		1,320,000,000	2,687,000,000		190,000,000												2,240,000,000	1,122,000,000	1,118,000,000	1,237,000,000	612,000,000	625,000,000	1,000,000,000	773,000,000	227,000,000
Ending Balance (Predecessor [Member]) at Dec. 31, 2015																																				4,413,000,000			3,832,000,000	[1]	617,000,000		(36,000,000)
Ending Balance at Dec. 31, 2015												12,942,000,000	2,701,000,000	(63,000,000)		1,307,000,000	8,997,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Predecessor [Member]																																				15,000,000			15,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 27,294,000,000			18,676,000,000	(2,327,000,000)	12,068,000,000	(2,624,000,000)	[2]	1,308,000,000	193,000,000			(63,000,000)	[2]											1,000,000	[2]
Other Additional Capital																		7,000,000		7,000,000
Retained Earnings, Appropriated																					(426,000,000)	426,000,000
Net Income (Loss) | Predecessor [Member]																																				19,000,000					19,000,000
Employee stock purchase plan issuances | Predecessor [Member]																																				3,000,000			3,000,000
Tax benefit on stock compensation | Predecessor [Member]																																				(1,000,000)
Other comprehensive income (loss), net of income taxes | Predecessor [Member]																																				1,000,000							1,000,000
Ending Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439,000,000			3,838,000,000	[1]	636,000,000		(35,000,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Predecessor [Member]																																				3,000,000			3,000,000
Beginning Balance (in shares) at Dec. 31, 2015		954,668
Beginning Balance at Dec. 31, 2015																		8,243,000,000	1,588,000,000	5,677,000,000	(1,639,000,000)	2,617,000,000	3,236,000,000	2,455,000,000	780,000,000	1,000,000		2,877,000,000		1,367,000,000		1,320,000,000	2,687,000,000		190,000,000												2,240,000,000	1,122,000,000	1,118,000,000	1,237,000,000	612,000,000	625,000,000	1,000,000,000	773,000,000	227,000,000
Beginning Balance (Predecessor [Member]) at Dec. 31, 2015																																				4,413,000,000			3,832,000,000	[1]	617,000,000		(36,000,000)
Beginning Balance at Dec. 31, 2015												12,942,000,000	2,701,000,000	(63,000,000)		1,307,000,000	8,997,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)		$ 1,204,000,000	$ (66,000,000)				1,134,000,000			62,000,000	8,000,000	558,000,000	496,000,000			62,000,000		378,000,000			378,000,000		438,000,000		438,000,000			294,000,000				294,000,000	294,000,000														42,000,000		42,000,000	(9,000,000)		(9,000,000)	(42,000,000)		(42,000,000)
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,868
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 85,000,000			85,000,000	0	0			0	0
Employee stock purchase plan issuances, shares		1,242
Employee stock purchase plan issuances		$ 55,000,000			55,000,000	0	0			0	0
Tax benefit on stock compensation		(18,000,000)			(18,000,000)
Noncontrolling Interest, Change in Redemption Value		157,000,000						0		157,000,000		(157,000,000)				(157,000,000)	0
Noncontrolling Interest, Period Increase (Decrease)		5,000,000			0					5,000,000		5,000,000				5,000,000
Noncontrolling interest acquired		239,000,000			(4,000,000)					243,000,000		239,000,000				243,000,000	4,000,000
Common stock dividends		(1,172,000,000)					(1,172,000,000)											(369,000,000)				(369,000,000)	(277,000,000)		(277,000,000)			(179,000,000)				(179,000,000)	(179,000,000)														(169,000,000)		(169,000,000)	(54,000,000)		(54,000,000)	(63,000,000)		(63,000,000)
Preferred and preference stock dividends		(8,000,000)									(8,000,000)																	(8,000,000)				(8,000,000)	(8,000,000)
Stock Redeemed or Called During Period, Value		(193,000,000)									(193,000,000)																	(190,000,000)							(190,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared		0										(922,000,000)	(922,000,000)			0
Temporary Equity, Other Changes												(157,000,000)
Adjustments to Additional Paid in Capital, Other		0										170,000,000					170,000,000	315,000,000		315,000,000								61,000,000	$ (7,000,000)	61,000,000	$ (7,000,000)		61,000,000	$ (7,000,000)	0												187,000,000	187,000,000		152,000,000	152,000,000		139,000,000	139,000,000
Income Tax Effects Allocated Directly to Equity, Other		0						0		0		98,000,000	0				98,000,000						18,000,000	18,000,000
Consolidated VIE dividend to noncontrolling interests																0
Other comprehensive income (loss), net of income taxes		$ (36,000,000)						(36,000,000)	[2]			9,000,000		9,000,000	[2]											0	[2]
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016		$ 25,837,000,000																8,725,000,000	1,588,000,000	6,150,000,000	(1,639,000,000)	2,626,000,000	3,415,000,000	2,473,000,000	941,000,000	1,000,000		2,848,000,000		1,421,000,000		1,427,000,000	2,848,000,000		0												2,300,000,000	1,309,000,000	991,000,000	1,326,000,000	764,000,000	562,000,000	1,034,000,000	912,000,000	122,000,000
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016,000,000						$ (61,000,000)	0	$ 8,077,000,000
Ending Balance at Dec. 31, 2016												13,256,000,000	2,275,000,000	(54,000,000)		1,774,000,000	9,261,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Additional Paid in Capital | Successor [Member]																																														$ 3,835,000,000
Common stock | Successor [Member]																																														3,000,000
Beginning Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439,000,000			$ 3,838,000,000	[1]	$ 636,000,000		(35,000,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) | Successor [Member]																																				(61,000,000)						(61,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]	[3]																																			(400,000,000)								(400,000,000)
Other comprehensive income (loss), net of income taxes | Successor [Member]																																				0
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid | Successor [Member]																																				53,000,000								53,000,000
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions | Successor [Member]																																				1,251,000,000								1,251,000,000
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016		$ 25,837,000,000																8,725,000,000	1,588,000,000	6,150,000,000	(1,639,000,000)	2,626,000,000	3,415,000,000	2,473,000,000	941,000,000	1,000,000		2,848,000,000		1,421,000,000		1,427,000,000	2,848,000,000		0												2,300,000,000	1,309,000,000	991,000,000	1,326,000,000	764,000,000	562,000,000	1,034,000,000	912,000,000	122,000,000
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016,000,000						(61,000,000)	0	8,077,000,000
Ending Balance at Dec. 31, 2016												13,256,000,000	2,275,000,000	(54,000,000)		1,774,000,000	9,261,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Successor [Member]				$ 33,000,000																																35,000,000	$ (62,000,000)							35,000,000	$ (62,000,000)
Stockholders' Equity, Other																																						$ 29,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		27,612,000,000			18,794,000,000	(2,327,000,000)	12,030,000,000	(2,660,000,000)	[2]	1,775,000,000	0			(54,000,000)	[2]											1,000,000	[2]
Other Additional Capital																		158,000,000		158,000,000
Retained Earnings, Appropriated																		2,626,000,000			(378,000,000)	378,000,000
Additional Paid in Capital | Predecessor [Member]																																														3,829,000,000
Additional Paid in Capital																		6,150,000,000
Common stock | Predecessor [Member]																																														$ 3,000,000
Common stock		18,794,000,000																1,588,000,000					2,473,000,000					1,421,000,000																			1,309,000,000			764,000,000			912,000,000
Net Income (Loss) | Successor [Member]																																				362,000,000						362,000,000
Net Income (Loss)		$ 3,849,000,000	$ 364,000,000				3,770,000,000			79,000,000	0	2,771,000,000	2,694,000,000			77,000,000		567,000,000			567,000,000		434,000,000		434,000,000			307,000,000				307,000,000	307,000,000														205,000,000		205,000,000	121,000,000		121,000,000	77,000,000		77,000,000
Stock Issued During Period, Shares, Share-based Compensation, Gross		5,066
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 56,000,000			56,000,000	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,324
Employee stock purchase plan issuances		$ 150,000,000			150,000,000	0	0	0		0	0
Stock Issued During Period, Value, Treasury Stock Reissued		1,150,000,000				2,204,000,000	(1,054,000,000)
Changes in equity of noncontrolling interests												18,000,000				18,000,000
Noncontrolling Interest, Change in Redemption Value		0
Noncontrolling Interest, Period Increase (Decrease)		(20,000,000)			0					(20,000,000)
Noncontrolling interest acquired		407,000,000			(36,000,000)	0	0	0		443,000,000	0	407,000,000	0	0		443,000,000	36,000,000
Common stock dividends		(1,243,000,000)					(1,243,000,000)											(422,000,000)				(422,000,000)	(288,000,000)		(288,000,000)			(198,000,000)				(198,000,000)	(198,000,000)														(133,000,000)		(133,000,000)	(112,000,000)		(112,000,000)	(68,000,000)		(68,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]	[3]																																			(311,000,000)						(311,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared										0		(659,000,000)	(659,000,000)	0
Adjustments to Additional Paid in Capital, Other																		651,000,000		651,000,000								184,000,000		184,000,000		0	184,000,000		0												161,000,000	161,000,000
Income Tax Effects Allocated Directly to Equity, Other		0										99,000,000					99,000,000						16,000,000	16,000,000												7,000,000								7,000,000
Other comprehensive income (loss), net of income taxes | Successor [Member]																																				0
Other comprehensive income (loss), net of income taxes		$ 171,000,000						173,000,000	[2]	(2,000,000)		15,000,000		17,000,000	[2]	(2,000,000)										0	[2]
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid												33,000,000					33,000,000
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions | Successor [Member]																																				751,000,000								751,000,000
Ending Balance (in shares) at Dec. 31, 2017		965,168
Ending Balance at Dec. 31, 2017		$ 29,857,000,000																9,542,000,000	$ 1,588,000,000	6,822,000,000	(1,639,000,000)	2,771,000,000	3,577,000,000	$ 2,489,000,000	$ 1,087,000,000	1,000,000		3,141,000,000		$ 1,605,000,000		$ 1,536,000,000	$ 3,141,000,000		$ 0												2,533,000,000	$ 1,470,000,000	$ 1,063,000,000	1,335,000,000	$ 764,000,000	$ 571,000,000	1,043,000,000	$ 912,000,000	$ 131,000,000
Ending Balance (Successor [Member]) at Dec. 31, 2017																																				$ 8,825,000,000						$ (10,000,000)	$ 0	$ 8,835,000,000
Ending Balance at Dec. 31, 2017												$ 15,904,000,000	$ 4,310,000,000	(37,000,000)		$ 2,274,000,000	$ 9,357,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		32,132,000,000			$ 18,964,000,000	$ (123,000,000)	$ 13,503,000,000	$ (2,487,000,000)	[2]	$ 2,275,000,000	$ 0			$ (37,000,000)	[2]											$ 1,000,000	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Additional Capital																		21,000,000		$ 21,000,000
Retained Earnings, Appropriated																		2,771,000,000			$ (567,000,000)	$ 567,000,000
Additional Paid in Capital																		6,822,000,000
Common stock		$ 18,964,000,000																$ 1,588,000,000					$ 2,489,000,000					$ 1,605,000,000																			$ 1,470,000,000			$ 764,000,000			$ 912,000,000

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

[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.