Mergers, Acquisitions and Dispositions Mergers, Acquisitions and Dispositions - Narrative (Details) $ in Millions										3 Months Ended										9 Months Ended			12 Months Ended
		Jul. 09, 2018 USD ($)	Apr. 04, 2018 USD ($)	Feb. 28, 2018 USD ($)	Nov. 07, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 01, 2016 USD ($)	Jun. 16, 2016 USD ($)	Mar. 23, 2016 USD ($)	Dec. 31, 2018 USD ($) MW	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 23, 2016 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) MW		Dec. 31, 2017 USD ($) MW		Dec. 31, 2016 USD ($)		Jun. 30, 2016 USD ($)	Mar. 24, 2016 USD ($)
Business Acquisition [Line Items]
Assets held for sale										$ 904				$ 0									$ 904		$ 0
Liabilities held for sale										777				0									777		0
Asset Retirement Obligation, Revision of Estimate																							20				$ 2
Deconsolidation, Gain (Loss), Amount					$ 213																		0		213		0
Business Combination, Contingent Consideration, Asset																														$ 235
Payments to Acquire Businesses, Gross																							154		208		6,923
Business Combination, Integration Related Costs																							7	[1]	16	[1]	143
Line of credit facility, maximum borrowing capacity	[2]									9,704													9,704
Other Commitment										127													127
Revenues										8,814	$ 9,403	$ 8,076	$ 9,693	8,384	$ 8,768	$ 7,665	$ 8,747						35,985		33,565		31,366
Business Combination, Bargain Purchase, Gain Recognized, Amount																							0		233		0
Net income (Loss)																							2,084		3,876		1,196
Noncash Merger Related Costs																							$ 0	[3]	$ 0	[4]	558	[5],[6]
Wind Assets [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW																							40
Exelon Corporation Affiliate [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment										$ 5													$ 5
Delmarva Power & Light Company [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW										40													120		40
Delmarva Power & Light Company [Member] | Remaining Commitment [Member]
Business Acquisition [Line Items]
Other Commitment										$ 12													$ 12
Exelon Consolidations [Member]
Business Acquisition [Line Items]
Other Commitment										508													508
Exelon Consolidations [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										259													259
Exelon Consolidations [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										29													29
Exelon Consolidations [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										117													117
Exelon Consolidations [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										50													50
Exelon Consolidations [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										22													22
Exelon Consolidations [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										14													14
Exelon Consolidations [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										17													17
Exelon Consolidations [Member] | Remaining Commitment [Member]
Business Acquisition [Line Items]
Other Commitment										128													128
Pepco Holdings [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross									$ 7,142
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Revenues																							4,670		$ 4,829		3,785
Net income (Loss)																							$ 453		$ 364		(66)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets									$ 4,005										$ 4,005
Pepco Holdings LLC [Member] | Other Solar Projects [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW																							27		37
Pepco Holdings LLC [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW																							100
Pepco Holdings LLC [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Commitment																		$ 513			$ 513	$ 513					513
Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Business Acquisition [Line Items]
Other Commitment										92													$ 92
ConEdison Solutions [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross							$ 257
Net Working Capital							$ 204
Oyster Creek [Member]
Business Acquisition [Line Items]
Assets held for sale										897													897
Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							0				0
Business Combination, Integration Related Costs																							1	[1],[7]	$ 4	[1],[7]	(1)
Revenues										799	731	662	977	813	738	674	951						3,169		3,176		3,233
Net income (Loss)										71	63	51	128	76	62	45	125						313		307		294
Noncash Merger Related Costs																							0	[3]	0	[4]	0	[5],[6]
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Assets held for sale										904				0									904		0
Liabilities held for sale										777				0									777		0
Asset Retirement Obligation, Revision of Estimate										203	84									$ 138			0				0
Deconsolidation, Gain (Loss), Amount																							0		213		0
Proceeds from Divestiture of Businesses				$ 87
Membership interest										9,518				9,357									9,518		9,357
Business Combination, Contingent Consideration, Asset																														163
Payments to Acquire Businesses, Gross																							154		208		293
Business Combination, Integration Related Costs																							5	[1]	22	[1]	37
Line of credit facility, maximum borrowing capacity										200		45											200
Gain (Loss) on Disposition of Property Plant Equipment																10											69
Proceeds from Sale of Productive Assets								$ 37
Revenues										5,069	5,278	4,579	5,512	4,657	4,750	4,216	4,878						20,437		18,500		17,757
Business Combination, Bargain Purchase, Gain Recognized, Amount																							0		233		0
Net income (Loss)																							443		2,798		550
Noncash Merger Related Costs																							0	[3]	0	[4]	53	[5],[6]
Asset Impairment Charges																		$ 23
Exelon Generation Co L L C [Member] | FirstEnergy [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 140
Exelon Generation Co L L C [Member] | Handley [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 62
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						$ 289																			289
Payments to Acquire Businesses, Gross																									110
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets														60											60
Business Combination, Integration Related Costs																									57
Business Combination, Consideration Transferred, Other						179																			54
Business Combination, Bargain Purchase, Gain Recognized, Amount																									233
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent														149											149
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets														114											114
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities														444											444
Total net assets														522											522
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						110
Payments to Acquire Businesses, Gross																									125
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Membership interest										9,220				8,835									9,220		8,835
Business Combination, Integration Related Costs																							0	[1],[7]	(6)	[1],[7]	28
Other Commitment						$ 444											444
Revenues										1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175						4,805		4,679
Net income (Loss)																							398		362
Noncash Merger Related Costs																							5	[3]	(8)	[4]
Impairment of Long-Lived Assets to be Disposed of																25
Pepco Holdings LLC [Member] | Predecessor [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																			0
Business Combination, Integration Related Costs	[7]																		29
Revenues																			1,153
Net income (Loss)																			19
Noncash Merger Related Costs	[5],[6]																		$ 0
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																						2	20
Business Combination, Contingent Consideration, Asset																														235
Business Combination, Integration Related Costs	[7]																					69	0		(18)	[1]
Business Combination, Consideration Transferred, Other																	59
Revenues																						3,643			4,679
Net income (Loss)																					$ (61)	(61)
Noncash Merger Related Costs	[5],[6]																					$ 317
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										320													320
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										264													264
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										6													6
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										50													50
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							22				0
Revenues										531	628	523	557	510	604	514	530						2,239		2,158		2,186
Net income (Loss)										36	89	54	31	17	87	43	58						210		205		42
Noncash Merger Related Costs																							0	[3]	(6)	[4]	125	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																														2,100
Fresh-Start Adjustment, Increase (Decrease), Goodwill																														400
Potomac Electric Power Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital																													$ 73
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										120													120
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										91													91
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										1													1
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										28													28
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							(1)				1
Business Combination, Integration Related Costs																							0	[1],[7]	(7)	[1],[7]	20
Revenues										331	328	289	384	330	327	282	362						1,332		1,300		1,277
Net income (Loss)										30	33	26	31	14	31	19	57						120		121		(9)
Noncash Merger Related Costs																							5	[3]	(2)	[4]	82	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																														1,400
Fresh-Start Adjustment, Increase (Decrease), Goodwill																														300
Delmarva Power & Light Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital																													46
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										89													89
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										72													72
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment										5													5
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										5													5
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										12													12
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							(1)				2
Business Combination, Integration Related Costs																							0	[1],[7]	(6)	[1],[7]	19
Revenues										254	406	265	310	271	370	270	275						1,236		1,186		1,257
Net income (Loss)										(1)	$ 61	8	$ 7	$ 0	$ 41	8	$ 28						75		77		(42)
Noncash Merger Related Costs																							0	[3]	$ 0	[4]	$ 110	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																														500
Fresh-Start Adjustment, Increase (Decrease), Goodwill																														$ (700)
Atlantic City Electric Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital																													$ 49
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										111													111
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										101													101
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										10													10
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Exelon Corporation Affiliate [Member] | Other commitments [Member]
Business Acquisition [Line Items]
Other Commitment										$ 83													$ 83
Electricity Generation Plant, Non-Nuclear [Member]
Business Acquisition [Line Items]
Impairment of Long-Lived Assets to be Disposed of												$ 41				$ 460				$ 460

[1] The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.

[2] Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

[3] See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[4] See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[5] Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.

[6] See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[7] (b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs as regulatory assets of $24 million, $8 million, $8 million, and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $8 million, $6 million, $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional information.