Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2018
Regulatory Liabilities		$ 10,388	$ 10,203
Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability	[1]	8,624
Regulatory Liabilities	[2]	7,315
Deferred Income Tax Expense (Benefit)	[1]	1,309
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		3,040
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		1,694
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		4,734
Exelon Generation Co L L C [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,895
Deferred Income Tax Expense (Benefit)		1,895
Commonwealth Edison Co [Member]
Regulatory Liabilities		6,577	6,343
Commonwealth Edison Co [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		2,819
Regulatory Liabilities	[2]	2,818
Deferred Income Tax Expense (Benefit)		1
Commonwealth Edison Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		1,400
Commonwealth Edison Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		573
Commonwealth Edison Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		1,973
PECO Energy Co [Member]
Regulatory Liabilities		690	596
PECO Energy Co [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,407
Regulatory Liabilities	[2]	1,394
Deferred Income Tax Expense (Benefit)		13
PECO Energy Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities	[3]	533
PECO Energy Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities	[3]	43
PECO Energy Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities	[3]	576
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities		1,163	1,269
Baltimore Gas and Electric Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,120
Regulatory Liabilities	[2]	1,124
Deferred Income Tax Expense (Benefit)		(4)
Baltimore Gas and Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		459
Baltimore Gas and Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		324
Baltimore Gas and Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		783
Pepco Holdings LLC [Member]
Regulatory Liabilities		1,928	1,948
Pepco Holdings LLC [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,944
Regulatory Liabilities	[2]	1,979
Deferred Income Tax Expense (Benefit)		(35)
Pepco Holdings LLC [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		648
Pepco Holdings LLC [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		754
Pepco Holdings LLC [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		1,402
Potomac Electric Power Company [Member]
Regulatory Liabilities		832	829
Potomac Electric Power Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		968
Regulatory Liabilities	[2]	976
Deferred Income Tax Expense (Benefit)		(8)
Potomac Electric Power Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		299
Potomac Electric Power Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		391
Potomac Electric Power Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		690
Delmarva Power & Light Company [Member]
Regulatory Liabilities		635	665
Delmarva Power & Light Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		540
Regulatory Liabilities	[2]	545
Deferred Income Tax Expense (Benefit)		(5)
Delmarva Power & Light Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		195
Delmarva Power & Light Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		194
Delmarva Power & Light Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		389
Atlantic City Electric Company [Member]
Regulatory Liabilities		422	$ 420
Atlantic City Electric Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		456
Regulatory Liabilities	[2]	458
Deferred Income Tax Expense (Benefit)		(2)
Atlantic City Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		153
Atlantic City Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		170
Atlantic City Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [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 was 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.