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Commitments and Contingencies - Environmental Issues Narrative (Details)
$ in Millions
1 Months Ended 6 Months Ended
Aug. 31, 2015
gal
Oct. 31, 2007
USD ($)
Jun. 30, 2016
USD ($)
MGPSite
gal
Exelon Generation Co L L C [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Consent decree penalty   $ 1  
Environmental loss contingencies     $ 11
PEPCO Holdings Inc [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Sites under study/remediation | MGPSite     9
Environmental Remediation Expense     $ 10
PEPCO Holdings Inc [Member] | Minimum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Loss Contingency, Estimate of Possible Loss     7
PEPCO Holdings Inc [Member] | Maximum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Loss Contingency, Estimate of Possible Loss     18
Potomac Electric Power Company [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
QuantityOfMineralOilSPill | gal 6,100    
Potomac Electric Power Company [Member] | Minimum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Environmental Exit Costs, Anticipated Cost     3
Potomac Electric Power Company [Member] | Maximum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Environmental Exit Costs, Anticipated Cost     $ 6
Delmarva Power and Light Company [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Total number of MGP sites | gal     2
Calpine Corporation [Member] | Maximum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Loss Contingency, Estimate of Possible Loss     $ 10
Sixty-Eighth Street Dump [Member] | Baltimore Gas and Electric Company [Member] | Minimum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Loss Contingency, Estimate of Possible Loss     50
Sixty-Eighth Street Dump [Member] | Baltimore Gas and Electric Company [Member] | Maximum [Member]      
Accrual For Environmental Loss Contingencies [Line Items]      
Loss Contingency, Estimate of Possible Loss     $ 64