Consolidated Statement of Changes in Shareholders Equity (Unaudited) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	Total		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] 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]	Exelon Generation Co L L C [Member] Undistributed Earnings [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member] Common Stock [Member]	Commonwealth Edison Co [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Commonwealth Edison Co [Member] Other Paid-In Capital [Member]	Commonwealth Edison Co [Member] Retained Deficit 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]	Baltimore Gas and Electric Company [Member] Membership Interest [Member]	Baltimore Gas and Electric Company [Member] Preference Stock Not Subject To Mandatory Redemption [Member]
Beginning Balance at Dec. 31, 2011	$ 14,388		$ 9,107	$ (2,327)	$ 10,055	$ (2,450)	$ 3																		$ 2,301	$ 1,294	$ 817	$ 2,111	$ 190
Beginning Balance (in shares) at Dec. 31, 2011	698,112
Beginning Balance at Dec. 31, 2011									8,708		915	5	3,556	4,232
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,171				1,160		(3)	14	558			(4)		562	379				379		381		381		4		4	4
Long-term incentive plan activity, shares	2,432
Long-term incentive plan activity	126		126
Employee stock purchase plan issuances	26		26
Employee stock purchase plan issuances, shares	857
Common stock dividends	(1,322)				(1,322)										(105)					(105)	(343)		(343)
Common stock issuance Constellation merger, shares	188,124
Common stock issuance Constellation merger	7,365		7,365						5,264				5,264
Noncontrolling interest acquired	114		8				106
BGE preference stock acquired	193							193
Preferred and preference stock dividends	(14)							(14)													(4)		(4)		(13)		(13)	(13)
Other comprehensive loss, net of income taxes	(317)								(402)		(402)				1		1				1			1
Allocation of tax benefit from parent									48												9
Other comprehensive loss, net of income taxes	(317)					(317)
Distribution to member									(1,626)					(1,626)
Allocation of tax benefit from member									48				48
Noncontrolling interest acquired									115			107	8
Allocation of tax benefit from parent															11			11			9	9
Appropriation of retained earnings for future dividends																			(379)	379
Contribution from parent																									66	66		66
Ending Balance at Dec. 31, 2012															7,323	1,588		5,014	(1,639)	2,360	2,982	2,388	593	1
Ending Balance at Dec. 31, 2012	21,730		16,632	(2,327)	9,893	(2,767)	106	193																	2,358	1,360	808	2,168	190
Ending Balance (in shares) at Dec. 31, 2012	889,525
Ending Balance at Dec. 31, 2012									12,665		513	108	8,876	3,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(4)	[1]							(18)						(81)						121				77
Ending Balance at Mar. 31, 2013
Beginning Balance at Dec. 31, 2012	21,730		16,632	(2,327)	9,893	(2,767)	106	193																	2,358		808	2,168	190
Beginning Balance (in shares) at Dec. 31, 2012	889,525
Beginning Balance at Dec. 31, 2012									12,665		513	108	8,876	3,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,729				1,719		(10)	20	1,060			(10)		1,070	249				249		395		395		210		210	210
Long-term incentive plan activity, shares	1,445
Long-term incentive plan activity	81		81
Employee stock purchase plan issuances	28		28
Employee stock purchase plan issuances, shares	1,064
Common stock dividends	(1,254)				(1,254)										(220)					(220)	(332)		(332)
Common stock issuance Constellation merger									(19)			(18)	(1)
Preferred and preference stock dividends	(14)							(14)													(1)		(1)		(13)		(13)	(13)
Other comprehensive loss, net of income taxes	727	[2]							(299)	[2]	(299)				0						0
Consolidated VIE dividend to noncontrolling interest	(63)						(63)		(63)			(63)
Deconsolidation of VIE	(18)						(18)
Redemption of preferred securities	(6)							(6)
Acquisition of noncontrolling interest									(3)				(3)
Allocation of tax benefit from parent																					27	27
Other comprehensive loss, net of income taxes	727					727
Distribution to member									(625)					(625)
Allocation of tax benefit from member									26				26
Allocation of tax benefit from parent															176			176			(6)		(6)
Appropriation of retained earnings for future dividends																			(249)	249
Ending Balance at Dec. 31, 2013	22,732														7,528	1,588	0	5,190	(1,639)	2,389	3,065	2,415	649	1	2,365
Ending Balance at Dec. 31, 2013	22,940		16,741	(2,327)	10,358	(2,040)	15	193																	2,555	1,360	1,005	2,365	190
Ending Balance (in shares) at Dec. 31, 2013	892,034
Ending Balance at Dec. 31, 2013									12,742		214	17	8,898	3,613
Beginning Balance at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	495								269						109						102				47
Ending Balance at Dec. 31, 2013	22,732														7,528	1,588	0				3,065			1	2,365
Ending Balance at Dec. 31, 2013	22,940			(2,327)																					2,555	1,360			190
Ending Balance (in shares) at Dec. 31, 2013	892,034
Ending Balance at Dec. 31, 2013									12,742
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	90								(185)						98						89				85
Ending Balance at Mar. 31, 2014
Beginning Balance at Dec. 31, 2013			16,741	(2,327)																						1,360			190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax benefit on stock compensation			(8)
Ending Balance at Sep. 30, 2014
Beginning Balance at Dec. 31, 2013	22,940		16,741	(2,327)	10,358	(2,040)	15	193																	2,555	1,360	1,005	2,365	190
Beginning Balance (in shares) at Dec. 31, 2013	892,034
Beginning Balance at Dec. 31, 2013									12,742		214	17	8,898	3,613
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,820				1,623		184	13	1,019			184		835	408				408		352		352		211		211	211
Long-term incentive plan activity, shares	1,574
Long-term incentive plan activity	72		72
Employee stock purchase plan issuances	35		35
Employee stock purchase plan issuances, shares	960
Common stock dividends	(1,071)				(1,071)										(307)					(307)	(320)		(320)
Noncontrolling interest acquired	1,548						1,548
Preferred and preference stock dividends	(13)							(13)																	(13)		(13)	(13)
Other comprehensive loss, net of income taxes	(644)								(250)						0						0
Consolidated VIE dividend to noncontrolling interest	(421)						(421)		1,548			1,548
Deconsolidation of VIE									(421)			(421)
Tax benefit on stock compensation	(8)
Acquisition of noncontrolling interest	4		(2)				6		5			5
Fair value of financing contract payments	(131)		(131)
Transfer of CENG pension and non-pension postretirement benefit obligations	2		2
Reversal of CENG equity method AOCI, net of income taxes	(116)					(116)
Other comprehensive loss, net of income taxes	(528)					(528)			(134)		(134)
Distribution to member									53				53
Allocation of tax benefit from member									(645)					(645)
Noncontrolling interest acquired									(116)		(116)
Allocation of tax benefit from parent															5			5			24	24
Appropriation of retained earnings for future dividends																			(408)	408
Contribution from parent	273																	273
Ending Balance at Dec. 31, 2014	22,608														7,907	1,588	0	5,468	(1,639)	2,490	3,121	2,439	681	1	2,563
Ending Balance at Dec. 31, 2014	24,133		16,709	(2,327)	10,910	(2,684)	1,332	193																	2,753	1,360	1,203	2,563	190
Ending Balance (in shares) at Dec. 31, 2014	894,568
Ending Balance at Dec. 31, 2014									14,051		(36)	1,333	8,951	3,803
Beginning Balance at Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18	[3]							(91)						73						98				52
Ending Balance at Dec. 31, 2014	22,608														7,907	1,588	0				3,121			1	2,563
Ending Balance at Dec. 31, 2014	24,133			(2,327)																					2,753	1,360			190
Ending Balance (in shares) at Dec. 31, 2014	894,568
Ending Balance at Dec. 31, 2014									$ 14,051

[1] Includes $265 million of interest expense related to the remeasurement of Exelon’s like-kind exchange tax position in the first quarter of 2013. See Note 14—Income Taxes of the Combined Notes to Consolidated Financial Statements for additional information.

[2] All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

[3] Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.