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Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Regulatory Assets [Line Items]      
Current $ 1,584   $ 759
Noncurrent 10,407   6,065
Regulatory Assets 11,991   6,824
Business Combination, Integration Related Costs 102 $ 108  
Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 4,261   3,156
Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1,861   1,616
AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 687   399
Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 198   189
Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 132   47
Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 896   162
Fair Value Of Supply Contract [Member]      
Regulatory Assets [Line Items]      
Current 1,535    
Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 8   9
Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 113   108
Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 276   286
Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 60   52
Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 265   247
Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 118   84
Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 47   2
Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 18   20
Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 77   87
Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 651   279
Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 5   6
ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 3   3
Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Current 0    
Regulatory Assets 61   29
Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Current 36    
Regulatory Assets     30
Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 12   0
Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 31   0
Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 43   6
Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 185   0
CAP Arrearage [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 8   7
AssetRemovalCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 397    
Under funded Benefit Post Retirement Obligation [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1,125    
Alternative Energy Credits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 7    
Commonwealth Edison Co [Member]      
Regulatory Assets [Line Items]      
Current 239   218
Noncurrent 925   895
Regulatory Assets 1,164   1,113
Business Combination, Integration Related Costs (8) 3  
Commonwealth Edison Co [Member] | UnderRecoveredElectricEnergyCosts [Member]      
Regulatory Assets [Line Items]      
ElectricTransmissionCostsUnderRecovery 18    
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 65   64
Commonwealth Edison Co [Member] | AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 149   140
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 198   189
UnderOverRecoveredDistributionServiceCosts 156   142
CostRecoveryForSignificantOneTimeEvents 42   47
RegulatoryAssetsDueToDeferredStormCosts 31   36
Business Combination, Integration Related Costs 9   11
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 45   46
Commonwealth Edison Co [Member] | Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 71   67
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 246   255
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 60   52
Commonwealth Edison Co [Member] | Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 265   247
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 56   43
Business Combination, Integration Related Costs 7   7
ElectricTransmissionCostsUnderRecovery 31   31
Underrecovered Electric Supply cost     5
Commonwealth Edison Co [Member] | Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   $ 0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0  
Commonwealth Edison Co [Member] | ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   $ 0
Commonwealth Edison Co [Member] | Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 9   10
Business Combination, Integration Related Costs 9    
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
Commonwealth Edison Co [Member] | Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Commonwealth Edison Co [Member] | Smart Meter Related Costs [Member]      
Regulatory Assets [Line Items]      
CostRecoveryForSignificantOneTimeEvents 2    
PECO Energy Co [Member]      
Regulatory Assets [Line Items]      
Current 42   34
Noncurrent 1,605   1,583
Regulatory Assets 1,647   1,617
Business Combination, Integration Related Costs 2 1  
PECO Energy Co [Member] | Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1,499   1,473
PECO Energy Co [Member] | AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 60   63
PECO Energy Co [Member] | Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1   1
PECO Energy Co [Member] | Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Fair Value Of Supply Contract [Member]      
Regulatory Assets [Line Items]      
Current 0    
PECO Energy Co [Member] | Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 22   22
PECO Energy Co [Member] | Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 29   30
PECO Energy Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   1
PECO Energy Co [Member] | Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   1
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1    
PECO Energy Co [Member] | Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 10   13
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PECO Energy Co [Member] | Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 17   6
PECO Energy Co [Member] | Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PECO Energy Co [Member] | CAP Arrearage [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 8   7
Baltimore Gas and Electric Company [Member]      
Regulatory Assets [Line Items]      
Current 266   267
Noncurrent 499   514
Regulatory Assets 765   781
Business Combination, Integration Related Costs 2 1  
Baltimore Gas and Electric Company [Member] | TransmissionCost [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 5   12
Baltimore Gas and Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 33   28
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 80   79
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Noncurrent 212   196
Regulatory Assets 212   196
Baltimore Gas and Electric Company [Member] | Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 8   8
Baltimore Gas and Electric Company [Member] | Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 8   9
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 19   19
Baltimore Gas and Electric Company [Member] | Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1   1
Baltimore Gas and Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 38   40
Baltimore Gas and Electric Company [Member] | Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 2   2
Baltimore Gas and Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 18   20
Baltimore Gas and Electric Company [Member] | Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 67   87
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 264   278
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 5   6
Baltimore Gas and Electric Company [Member] | ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 3   3
Baltimore Gas and Electric Company [Member] | Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 4   3
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Current 36    
Regulatory Assets     30
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     30
Baltimore Gas and Electric Company [Member] | Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Baltimore Gas and Electric Company [Member] | Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
PEPCO Holdings Inc [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Current     305
Noncurrent     2,277
Regulatory Assets     2,582
PEPCO Holdings Inc [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Current 801    
Noncurrent 3,202    
Regulatory Assets 4,003    
PEPCO Holdings Inc [Member] | TransmissionCost [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 4   5
PEPCO Holdings Inc [Member] | Other Postretirement Benefits [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     910
PEPCO Holdings Inc [Member] | Other Postretirement Benefits [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Deferred Income Tax Charge [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     214
PEPCO Holdings Inc [Member] | Deferred Income Tax Charge [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 217    
PEPCO Holdings Inc [Member] | AMI Expenses [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     267
PEPCO Holdings Inc [Member] | AMI Expenses [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 266    
PEPCO Holdings Inc [Member] | Under Recovered Distribution Service Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Under Recovered Distribution Service Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Loss on Reacquired Debt [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     36
PEPCO Holdings Inc [Member] | Loss on Reacquired Debt [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 86    
PEPCO Holdings Inc [Member] | Fair Value Of Long Term Debt [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Fair Value Of Long Term Debt [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 741    
PEPCO Holdings Inc [Member] | Fair Value Of Supply Contract [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1,535    
PEPCO Holdings Inc [Member] | Employee Severance [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Employee Severance [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Asset Retirement Obligation Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     1
PEPCO Holdings Inc [Member] | Asset Retirement Obligation Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1    
PEPCO Holdings Inc [Member] | Environmental Restoration Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Environmental Restoration Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Under Recovered Uncollectible Accounts Expense [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Under Recovered Uncollectible Accounts Expense [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Renewable Energy And Associated REC [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Renewable Energy And Associated REC [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Under Recovered Energy And Transmission Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     33
PEPCO Holdings Inc [Member] | Under Recovered Energy And Transmission Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 24    
PEPCO Holdings Inc [Member] | Deferred Storm Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     43
PEPCO Holdings Inc [Member] | Deferred Storm Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 45    
PEPCO Holdings Inc [Member] | Electric Generation Related Regulatory Asset [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Electric Generation Related Regulatory Asset [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Rate Stabilization Deferral [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     14
PEPCO Holdings Inc [Member] | Rate Stabilization Deferral [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 10    
PEPCO Holdings Inc [Member] | Energy Efficiency And Demand Response Programs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     401
PEPCO Holdings Inc [Member] | Energy Efficiency And Demand Response Programs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 386    
PEPCO Holdings Inc [Member] | Merger Integration Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Merger Integration Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | ConservativeVoltageReductionProgram [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | ConservativeVoltageReductionProgram [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
PEPCO Holdings Inc [Member] | Regulatory Assets [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     38
PEPCO Holdings Inc [Member] | Regulatory Assets [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 34    
PEPCO Holdings Inc [Member] | Under Recovered Decoupling Revenue [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Deferred Project Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
PEPCO Holdings Inc [Member] | Workers Compensation and Long-Term Disability [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     31
PEPCO Holdings Inc [Member] | Workers Compensation and Long-Term Disability [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 31    
PEPCO Holdings Inc [Member] | Recoverable Vacation Pay [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     23
PEPCO Holdings Inc [Member] | Recoverable Vacation Pay [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 26    
PEPCO Holdings Inc [Member] | Stranded Costs [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     202
PEPCO Holdings Inc [Member] | Stranded Costs [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 185    
PEPCO Holdings Inc [Member] | AssetRemovalCosts [Member] | Predecessor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     369
PEPCO Holdings Inc [Member] | AssetRemovalCosts [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 397    
PEPCO Holdings Inc [Member] | Alternative Energy Credits [Member] | Successor [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 7    
Potomac Electric Power Company [Member]      
Regulatory Assets [Line Items]      
Current 133   140
Noncurrent 663   661
Regulatory Assets 796   801
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1    
Potomac Electric Power Company [Member] | Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 139   137
Potomac Electric Power Company [Member] | AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 181   $ 180
Potomac Electric Power Company [Member] | Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0  
Potomac Electric Power Company [Member] | Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 19   $ 19
Potomac Electric Power Company [Member] | Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1   1
Potomac Electric Power Company [Member] | Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 5   9
Potomac Electric Power Company [Member] | Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 19   19
Potomac Electric Power Company [Member] | Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 9   10
Potomac Electric Power Company [Member] | Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 277   289
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 12   14
Potomac Electric Power Company [Member] | Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
Potomac Electric Power Company [Member] | Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 31   31
Potomac Electric Power Company [Member] | Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Potomac Electric Power Company [Member] | AssetRemovalCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 103   92
Delmarva Power and Light Company [Member]      
Regulatory Assets [Line Items]      
Current 67   72
Noncurrent 295   299
Regulatory Assets 362   371
Business Combination, Integration Related Costs 16 1  
Delmarva Power and Light Company [Member] | TransmissionCost [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     7
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     1
Delmarva Power and Light Company [Member] | Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 35   36
Delmarva Power and Light Company [Member] | AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 85   $ 87
Delmarva Power and Light Company [Member] | Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0  
Delmarva Power and Light Company [Member] | Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 9   $ 10
Delmarva Power and Light Company [Member] | Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 6   11
Delmarva Power and Light Company [Member] | Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 6   6
Delmarva Power and Light Company [Member] | Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1   4
Delmarva Power and Light Company [Member] | Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 108   111
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 12   10
Delmarva Power and Light Company [Member] | Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
Delmarva Power and Light Company [Member] | Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 12   13
Delmarva Power and Light Company [Member] | Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 15   14
Delmarva Power and Light Company [Member] | Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Delmarva Power and Light Company [Member] | AssetRemovalCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 73   69
Atlantic City Electric Company [Member]      
Regulatory Assets [Line Items]      
Current 95   98
Noncurrent 419   414
Regulatory Assets 514   512
Business Combination, Integration Related Costs 13 $ 1  
Atlantic City Electric Company [Member] | TransmissionCost [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1   2
Atlantic City Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 12   11
Atlantic City Electric Company [Member] | Other Postretirement Benefits [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Deferred Income Tax Charge [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 43   41
Atlantic City Electric Company [Member] | AMI Expenses [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   $ 0
Atlantic City Electric Company [Member] | Under Recovered Distribution Service Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0  
Atlantic City Electric Company [Member] | Loss on Reacquired Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 7   $ 7
Atlantic City Electric Company [Member] | Fair Value Of Long Term Debt [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Fair Value Of Supply Contract [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
Atlantic City Electric Company [Member] | Employee Severance [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Asset Retirement Obligation Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Environmental Restoration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Renewable Energy And Associated REC [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 13   13
Atlantic City Electric Company [Member] | Deferred Storm Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 20   18
Atlantic City Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0    
Atlantic City Electric Company [Member] | Rate Stabilization Deferral [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 1   1
Atlantic City Electric Company [Member] | Merger Integration Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | ConservativeVoltageReductionProgram [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Regulatory Assets [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 12   13
Atlantic City Electric Company [Member] | Under Recovered Decoupling Revenue [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets     0
Atlantic City Electric Company [Member] | Deferred Project Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Workers Compensation and Long-Term Disability [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 0   0
Atlantic City Electric Company [Member] | Recoverable Vacation Pay [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 11   9
Atlantic City Electric Company [Member] | Stranded Costs [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets 185   202
Atlantic City Electric Company [Member] | AssetRemovalCosts [Member]      
Regulatory Assets [Line Items]      
Regulatory Assets $ 222   $ 208