Mergers, Acquisitions and Dispositions Mergers, Acquisitions and Dispositions - Narrative (Details)							1 Months Ended	3 Months Ended											6 Months Ended	9 Months Ended		12 Months Ended
		Nov. 07, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 01, 2016 USD ($)	Jun. 16, 2016 USD ($)	Mar. 23, 2016 USD ($) $ / shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)		Mar. 23, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)		Dec. 31, 2018 MW	Dec. 31, 2017 USD ($) MW		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)	Nov. 30, 2016 USD ($)	Mar. 24, 2016 USD ($)
Business Acquisition [Line Items]
Deconsolidation, Gain (Loss), Amount		$ 213,000,000																					$ 213,000,000		$ 0		$ 0
Acquisition Costs, Period Cost		$ 60,000,000
Business Combination, Contingent Consideration, Asset																													$ 235,000,000
Payments to Acquire Businesses, Gross																							208,000,000		6,934,000,000		40,000,000
Business Combination, Integration Related Costs	[1]																						16,000,000		143,000,000
Line of credit facility, maximum borrowing capacity																												$ 98
Share price | $ / shares						$ 27.25											$ 27.25
Other Commitment								$ 137,000,000															137,000,000
Payments to Acquire Businesses, Net of Cash Acquired																									(6,962,000,000)		0
Revenues								8,381,000,000	$ 8,769,000,000	$ 7,623,000,000	$ 8,757,000,000	$ 7,875,000,000	$ 9,002,000,000	$ 6,910,000,000	$ 7,573,000,000								33,531,000,000		31,360,000,000		29,447,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount																							233,000,000		0		0
Net income (Loss)																							3,849,000,000		1,204,000,000		2,250,000,000
Noncash Merger Related Costs																							0	[2]	558,000,000	[3],[4]
Payments of Debt Restructuring Costs	[5]																										22,000,000
Other Intangible Assets [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired																							1,500,000,000
Pepco Holdings [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 7,142,000,000
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets						1,441,000,000											$ 1,441,000,000
Other Commitment								513,000,000															513,000,000
Revenues																							4,829,000,000		3,785,000,000
Net income (Loss)																							$ 364,000,000		(66,000,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent						3,447,000,000											3,447,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets						248,000,000											248,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets						4,005,000,000											4,005,000,000
Total net assets						7,142,000,000											7,142,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt						5,636,000,000											5,636,000,000
Pepco Holdings LLC [Member] | Other Solar Projects [Member]
Business Acquisition [Line Items]
OtherNonFinancialCommitment1 | MW																						27,000,000	37,000,000
Pepco Holdings LLC [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
OtherNonFinancialCommitment1 | MW																							100,000,000
Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment							$ 8,000,000			8,000,000
Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								29,000,000															$ 29,000,000
Pepco Holdings LLC [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Commitment								513,000,000															513,000,000
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			$ 289,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets			60,000,000								60,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount																							233,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent			149,000,000								149,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	[6]		114,000,000								114,000,000
Total net assets			522,000,000								522,000,000
Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other			54,000,000
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			110,000,000
Business Combination, Consideration Transferred, Other			125,000,000
ConEdison Solutions [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross				$ 257,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets				9,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities				65,000,000
Total net assets				257,000,000
Net Working Capital				$ 204,000,000
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Deconsolidation, Gain (Loss), Amount																							213,000,000		0		0
Membership interest								9,357,000,000				9,261,000,000								$ 9,261,000,000			9,357,000,000		9,261,000,000
Business Combination, Contingent Consideration, Asset																													163,000,000
Payments to Acquire Businesses, Gross																							208,000,000		293,000,000		40,000,000
Business Combination, Integration Related Costs	[1]																						22,000,000		37,000,000
Line of credit facility, maximum borrowing capacity								200,000,000															200,000,000
Gain (Loss) on Disposition of Property Plant Equipment												69,000,000		10,000,000					$ 32,000,000
Proceeds from Sale of Productive Assets					$ 37,000,000
Revenues							12,000,000	4,654,000,000	4,751,000,000	4,174,000,000	4,888,000,000	4,388,000,000	5,035,000,000	3,589,000,000	4,739,000,000								18,466,000,000		17,751,000,000		19,135,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount																							233,000,000		0		0
Net income (Loss)																							2,771,000,000		558,000,000		1,340,000,000
Noncash Merger Related Costs																							0	[2]	53,000,000	[3],[4]
Payments of Debt Restructuring Costs																											0
Asset Impairment Charges												23,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			289,000,000
Business Combination, Integration Related Costs																							57,000,000
Business Combination, Consideration Transferred, Other			179,000,000
Total net assets									3,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																							54,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			110,000,000
Payments to Acquire Businesses, Gross									4,000,000														235,000,000
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[1],[7]																						(6,000,000)		28,000,000
Gain (Loss) on Disposition of Property Plant Equipment																		$ 37,000,000									9,000,000
Other Commitment			$ 444,000,000								444,000,000
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent																													59,000,000
Pepco Holdings LLC [Member] | Predecessor [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																	0
Business Combination, Integration Related Costs	[7],[8]																29,000,000
Revenues																	1,153,000,000										4,935,000,000
Net income (Loss)																	19,000,000										327,000,000
Noncash Merger Related Costs	[3],[4]																$ 0
Payments of Debt Restructuring Costs																											0
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Membership interest								8,835,000,000				8,077,000,000								8,077,000,000			8,835,000,000		8,077,000,000				7,200,000,000
Business Combination, Contingent Consideration, Asset																													235,000,000
Payments to Acquire Businesses, Gross																				29,000,000
Business Combination, Integration Related Costs	[7],[8]																			69,000,000			(18,000,000)
Business Combination, Consideration Transferred, Other															59,000,000
Revenues								1,121,000,000	1,310,000,000	1,074,000,000	1,175,000,000	1,078,000,000	1,394,000,000	1,066,000,000	105,000,000	[9]				3,643,000,000			4,679,000,000
Net income (Loss)																				(61,000,000)			362,000,000
Noncash Merger Related Costs																				$ 317,000,000	[3],[4]		(8,000,000)	[2]
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Other Commitment								315,000,000															315,000,000
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Other1 [Member] | Successor [Member]
Business Acquisition [Line Items]
Other Commitment								6,000,000															6,000,000
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																									0
Gain (Loss) on Disposition of Property Plant Equipment																			8,000,000
Other Commitment								86,000,000															86,000,000
Revenues								510,000,000	604,000,000	514,000,000	530,000,000	491,000,000	635,000,000	509,000,000	551,000,000								2,158,000,000		2,186,000,000		2,129,000,000
Net income (Loss)																							205,000,000		42,000,000		187,000,000
Noncash Merger Related Costs																							(6,000,000)	[2]	125,000,000	[3],[4]
Payments of Debt Restructuring Costs																											0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																													1,700,000,000
Potomac Electric Power Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital														73,000,000					73,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								120,000,000															120,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment							6,000,000			6,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								1,000,000															1,000,000
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																									0
Business Combination, Integration Related Costs	[1],[7]																						(7,000,000)		20,000,000
Gain (Loss) on Disposition of Property Plant Equipment												5,000,000	4,000,000
Other Commitment								27,000,000															27,000,000
Revenues								330,000,000	327,000,000	282,000,000	362,000,000	303,000,000	331,000,000	281,000,000	362,000,000								1,300,000,000		1,277,000,000		1,302,000,000
Net income (Loss)																							121,000,000		(9,000,000)		76,000,000
Noncash Merger Related Costs																							(2,000,000)	[2]	82,000,000	[3],[4]
Payments of Debt Restructuring Costs																											0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																													1,100,000,000
Delmarva Power and Light Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital														46,000,000					46,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								84,000,000															84,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment							$ 2,000,000			2,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								5,000,000															5,000,000
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																									0
Business Combination, Integration Related Costs	[1],[7]																						(6,000,000)		19,000,000
Other Commitment								121,000,000															121,000,000
Revenues								271,000,000	$ 370,000,000	270,000,000	$ 275,000,000	$ 275,000,000	$ 421,000,000	270,000,000	$ 291,000,000								1,186,000,000		1,257,000,000		1,295,000,000
Net income (Loss)																							77,000,000		(42,000,000)		40,000,000
Noncash Merger Related Costs																							0	[2]	$ 110,000,000	[3],[4]
Payments of Debt Restructuring Costs																											$ 0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																													$ 1,200,000,000
Atlantic City Electric Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital														$ 49,000,000					$ 49,000,000
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								111,000,000															111,000,000
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								$ 0															0
Preferred Stock [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																							$ 180,000,000
Preferred Stock [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 180,000,000
Electricity Generation Plant, Non-Nuclear [Member]
Business Acquisition [Line Items]
Impairment of Long-Lived Assets to be Disposed of										$ 460,000,000

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

[3] 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.

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

[5] (e)See Note 13—Debt and Credit Agreements and Note 4—Mergers, Acquisitions and Dispositions for additional information on the PHI merger related debt exchange.

[6] (a)Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 23-Commitments and Contingencies for additional background regarding SNF obligations to the DOE.

[7] (b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million, $8 million, $8 million, and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million, $6 million, $11 million, and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information.

[8] (a)Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.

[9] Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.