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Commitments and Contingencies Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | $ 496 | $ 466
Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 356 | 315
Exelon Generation Co L L C [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 108 | 117
Exelon Generation Co L L C [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 0 | 0
Commonwealth Edison Co [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 329 | 285
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 327 | 283
PECO Energy Co [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 27 | 30
PECO Energy Co [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 25 | 28
Baltimore Gas and Electric Company [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 5 | 5
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 4 | 4
Pepco Holdings LLC [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 27 | 29
Pepco Holdings LLC [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 0 | 0
Potomac Electric Power Company [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 25 | 27
Potomac Electric Power Company [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 0 | 0
Delmarva Power & Light Company [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 1 | 1
Delmarva Power & Light Company [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 0 | 0
Atlantic City Electric Company [Member] | Total Accrual For Environmental Loss Contingencies [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | 1 | 1
Atlantic City Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member] |  |
Loss Contingencies [Line Items] |  |
Accrual for Environmental Loss Contingencies, Gross | $ 0 | $ 0

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