Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended			12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	[1]	Jun. 30, 2018	Jun. 30, 2017	[1]	Dec. 31, 2017	Jul. 27, 2018	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%	[2]	21.00%	35.00%	[2]	35.00%
Allowable Expensing For Cost Of Qualified Property					30.00%
Limitation on Deductible Interest Expense					100.00%
Bonus Depreciation Percentage					50.00%
Net Regulatory Liabilities		$ 10,378			$ 10,378			$ 10,388
Decrease in Unrecognized Tax Benefits is Reasonably Possible		681			681
Unrecognized tax benefits that if recognized would affect the effective tax rate		444			444
Increase (Decrease) in Other Deferred Liability		16
Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 33			33
Deferred Gain on Sale of Property										$ 1,200
IRS asserted penalties for understatement of tax					$ 90
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%	[3]	21.00%	35.00%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 458			$ 458
Unrecognized tax benefits that if recognized would affect the effective tax rate		444			$ 444
Increase (Decrease) in Other Deferred Liability		$ 5
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 6,508			$ 6,508			6,577
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 2			$ 2
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 713			$ 713			690
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 1,176			$ 1,176			1,163
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 120			$ 120
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 1,959			$ 1,959			1,928
Decrease in Unrecognized Tax Benefits is Reasonably Possible		103			$ 103
Increase (Decrease) in Other Deferred Liability		$ 17
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 821			$ 821			832
Decrease in Unrecognized Tax Benefits is Reasonably Possible		68			$ 68
Increase (Decrease) in Other Deferred Liability		$ 16
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 655			$ 655			635
Decrease in Unrecognized Tax Benefits is Reasonably Possible		21			$ 21
Increase (Decrease) in Other Deferred Liability		$ 1
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		21.00%	35.00%
Net Regulatory Liabilities		$ 447			$ 447			422
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 14			$ 14
Remeasurement Of Deferred Income Taxes Due To Tax Reform
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							7,315
Increase (Decrease) in Other Deferred Liability	[5]							8,624
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Other Deferred Liability								1,895
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							2,818
Increase (Decrease) in Other Deferred Liability								2,819
Remeasurement Of Deferred Income Taxes Due To Tax Reform | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4],[6]							1,394
Increase (Decrease) in Other Deferred Liability								1,407
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							1,124
Increase (Decrease) in Other Deferred Liability								1,120
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							1,979
Increase (Decrease) in Other Deferred Liability								1,944
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							976
Increase (Decrease) in Other Deferred Liability								968
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							545
Increase (Decrease) in Other Deferred Liability								540
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[4]							458
Increase (Decrease) in Other Deferred Liability								456
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								3,040
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								1,400
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[7]							533
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								459
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								648
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								299
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								195
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								153
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								1,694
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								573
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[7]							43
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								324
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								754
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								391
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								194
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								170
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								4,734
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								1,973
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[7]							576
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								783
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								1,402
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								690
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								389
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities								$ 323
Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate									$ 25
Increase in Unrecognized Tax Benefits is Reasonably Possible									$ 75

[1] Exelon retrospectively adopted the new standard Revenue from Contracts with Customers. The standard was adopted as of January 1, 2018. The effective income tax rates are recast to reflect the impact of the new standard.

[2] The effective tax rate for the three months ended June 30, 2017 is disproportionately impacted due to the decline in consolidated pre-tax GAAP earnings as compared to the federal and state tax impacts of the Like-kind exchange, tax credits, Plant basis differences, and Qualified nuclear decommissioning trust fund income.

[3] Generation recognized a loss before income taxes for the three months ended June 30, 2017. As a result, positive percentages represent an income tax benefit for the period presented.

[4] 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.

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

[6] 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.

[7] 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.