Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Sep. 30, 2018
Net Regulatory Liability Recorded		$ 10,388	$ 10,445
Commonwealth Edison Co [Member]
Net Regulatory Liability Recorded		6,577	6,638
PECO Energy Co [Member]
Net Regulatory Liability Recorded		690	740
Baltimore Gas and Electric Company [Member]
Net Regulatory Liability Recorded		1,163	1,165
Pepco Holdings LLC [Member]
Net Regulatory Liability Recorded		1,928	1,882
Potomac Electric Power Company [Member]
Net Regulatory Liability Recorded		832	764
Delmarva Power and Light Company [Member]
Net Regulatory Liability Recorded		635	654
Atlantic City Electric Company [Member]
Net Regulatory Liability Recorded		422	$ 428
Remeasurement Of Deferred Income Taxes Due To Tax Reform
Net Decrease to Deferred Income Tax Liability Balances	[1]	8,624
Net Regulatory Liability Recorded	[2]	7,315
Net Deferred Income Tax Benefit/(Expense) Recorded	[1]	1,309
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Exelon Generation Co L L C [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,895
Net Deferred Income Tax Benefit/(Expense) Recorded		1,895
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Commonwealth Edison Co [Member]
Net Decrease to Deferred Income Tax Liability Balances		2,819
Net Regulatory Liability Recorded	[2]	2,818
Net Deferred Income Tax Benefit/(Expense) Recorded		1
Remeasurement Of Deferred Income Taxes Due To Tax Reform | PECO Energy Co [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,407
Net Regulatory Liability Recorded	[2],[3]	1,394
Net Deferred Income Tax Benefit/(Expense) Recorded		13
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Baltimore Gas and Electric Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,120
Net Regulatory Liability Recorded	[2]	1,124
Net Deferred Income Tax Benefit/(Expense) Recorded		(4)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Pepco Holdings LLC [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,944
Net Regulatory Liability Recorded	[2]	1,979
Net Deferred Income Tax Benefit/(Expense) Recorded		(35)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Potomac Electric Power Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		968
Net Regulatory Liability Recorded	[2]	976
Net Deferred Income Tax Benefit/(Expense) Recorded		(8)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Delmarva Power and Light Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		540
Net Regulatory Liability Recorded	[2]	545
Net Deferred Income Tax Benefit/(Expense) Recorded		(5)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Atlantic City Electric Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		456
Net Regulatory Liability Recorded	[2]	458
Net Deferred Income Tax Benefit/(Expense) Recorded		$ (2)

[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 was in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. See Note 6 - Regulatory Matters for additional information.