Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Regulatory Liabilities		$ 10,246	$ 10,388
Commonwealth Edison Co [Member]
Regulatory Liabilities		6,424	6,577
PECO Energy Co [Member]
Regulatory Liabilities		646	690
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities		1,185	1,163
Pepco Holdings LLC [Member]
Regulatory Liabilities		1,965	1,928
Potomac Electric Power Company [Member]
Regulatory Liabilities		845	832
Delmarva Power and Light Company [Member]
Regulatory Liabilities		646	635
Atlantic City Electric Company [Member]
Regulatory Liabilities		437	422
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability	[1]	8,624
Deferred Income Tax Expense (Benefit)	[1]	1,309
Regulatory Liabilities	[2]	7,315
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Exelon Generation Co L L C [Member]
Increase (Decrease) in Other Deferred Liability		1,895
Deferred Income Tax Expense (Benefit)		1,895
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Commonwealth Edison Co [Member]
Increase (Decrease) in Other Deferred Liability		2,819
Deferred Income Tax Expense (Benefit)		1
Regulatory Liabilities	[2]	2,818
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | PECO Energy Co [Member]
Increase (Decrease) in Other Deferred Liability		1,407
Deferred Income Tax Expense (Benefit)		13
Regulatory Liabilities	[2],[3]	1,394
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Baltimore Gas and Electric Company [Member]
Increase (Decrease) in Other Deferred Liability		1,120
Deferred Income Tax Expense (Benefit)		(4)
Regulatory Liabilities	[2]	1,124
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Pepco Holdings LLC [Member]
Increase (Decrease) in Other Deferred Liability		1,944
Deferred Income Tax Expense (Benefit)		(35)
Regulatory Liabilities	[2]	1,979
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Potomac Electric Power Company [Member]
Increase (Decrease) in Other Deferred Liability		968
Deferred Income Tax Expense (Benefit)		(8)
Regulatory Liabilities	[2]	976
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Delmarva Power and Light Company [Member]
Increase (Decrease) in Other Deferred Liability		540
Deferred Income Tax Expense (Benefit)		(5)
Regulatory Liabilities	[2]	545
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Atlantic City Electric Company [Member]
Increase (Decrease) in Other Deferred Liability		456
Deferred Income Tax Expense (Benefit)		(2)
Regulatory Liabilities	[2]	$ 458
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities			3,040
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Commonwealth Edison Co [Member]
Regulatory Liabilities			1,400
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | PECO Energy Co [Member]
Regulatory Liabilities	[4]		533
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Liabilities			459
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Pepco Holdings LLC [Member]
Regulatory Liabilities			648
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Potomac Electric Power Company [Member]
Regulatory Liabilities			299
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Delmarva Power and Light Company [Member]
Regulatory Liabilities			195
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Atlantic City Electric Company [Member]
Regulatory Liabilities			153
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities			1,694
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Commonwealth Edison Co [Member]
Regulatory Liabilities	[4]		573
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | PECO Energy Co [Member]
Regulatory Liabilities	[4]		43
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Liabilities			324
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Pepco Holdings LLC [Member]
Regulatory Liabilities			754
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Potomac Electric Power Company [Member]
Regulatory Liabilities			391
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Delmarva Power and Light Company [Member]
Regulatory Liabilities			194
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Atlantic City Electric Company [Member]
Regulatory Liabilities			170
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities			4,734
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Commonwealth Edison Co [Member]
Regulatory Liabilities			1,973
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | PECO Energy Co [Member]
Regulatory Liabilities	[4]		576
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Liabilities			783
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Pepco Holdings LLC [Member]
Regulatory Liabilities			1,402
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Potomac Electric Power Company [Member]
Regulatory Liabilities			690
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Delmarva Power and Light Company [Member]
Regulatory Liabilities			389
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Atlantic City Electric Company [Member]
Regulatory Liabilities			$ 323

[1] Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans.

[2] Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers.

[3] Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information.

[4] Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information.