Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Net Decrease to Deferred Income Tax Liability Balances		$ 16
Net Regulatory Liability Recorded		10,378	$ 10,388
Exelon Generation Co L L C [Member]
Net Decrease to Deferred Income Tax Liability Balances		5
Commonwealth Edison Co [Member]
Net Regulatory Liability Recorded		6,508	6,577
PECO Energy Co [Member]
Net Regulatory Liability Recorded		713	690
Baltimore Gas and Electric Company [Member]
Net Regulatory Liability Recorded		1,176	1,163
Pepco Holdings LLC [Member]
Net Decrease to Deferred Income Tax Liability Balances		17
Net Regulatory Liability Recorded		1,959	1,928
Potomac Electric Power Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		16
Net Regulatory Liability Recorded		821	832
Delmarva Power and Light Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		1
Net Regulatory Liability Recorded		655	635
Atlantic City Electric Company [Member]
Net Regulatory Liability Recorded		$ 447	422
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)
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules
Net Regulatory Liability Recorded			3,040
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Commonwealth Edison Co [Member]
Net Regulatory Liability Recorded			1,400
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | PECO Energy Co [Member]
Net Regulatory Liability Recorded	[4]		533
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Baltimore Gas and Electric Company [Member]
Net Regulatory Liability Recorded			459
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Pepco Holdings LLC [Member]
Net Regulatory Liability Recorded			648
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Potomac Electric Power Company [Member]
Net Regulatory Liability Recorded			299
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Delmarva Power and Light Company [Member]
Net Regulatory Liability Recorded			195
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Atlantic City Electric Company [Member]
Net Regulatory Liability Recorded			153
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations
Net Regulatory Liability Recorded			1,694
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Commonwealth Edison Co [Member]
Net Regulatory Liability Recorded			573
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | PECO Energy Co [Member]
Net Regulatory Liability Recorded	[4]		43
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Baltimore Gas and Electric Company [Member]
Net Regulatory Liability Recorded			324
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Pepco Holdings LLC [Member]
Net Regulatory Liability Recorded			754
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Potomac Electric Power Company [Member]
Net Regulatory Liability Recorded			391
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Delmarva Power and Light Company [Member]
Net Regulatory Liability Recorded			194
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Atlantic City Electric Company [Member]
Net Regulatory Liability Recorded			170
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers
Net Regulatory Liability Recorded			4,734
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Commonwealth Edison Co [Member]
Net Regulatory Liability Recorded			1,973
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | PECO Energy Co [Member]
Net Regulatory Liability Recorded	[4]		576
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Baltimore Gas and Electric Company [Member]
Net Regulatory Liability Recorded			783
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Pepco Holdings LLC [Member]
Net Regulatory Liability Recorded			1,402
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Potomac Electric Power Company [Member]
Net Regulatory Liability Recorded			690
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Delmarva Power and Light Company [Member]
Net Regulatory Liability Recorded			389
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Atlantic City Electric Company [Member]
Net Regulatory Liability Recorded			$ 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 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.

[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. See Note 6 - Regulatory Matters for additional information.