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Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($)
$ in Millions
Jun. 30, 2018
Dec. 31, 2017
Regulatory Assets [Line Items]    
Regulatory Assets $ 9,316 $ 9,288
Current 1,293 1,267
Regulatory Assets, Noncurrent 8,023 8,021
Pension and Other Postretirement Plans Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [1] 3,777 3,848
Deferred Income Tax Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 363 306
Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 602 640
Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [2] 243 244
Energy Efficiency Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 284 166
Loss on Reacquired Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 105 116
Fair Value Of Long Term Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 730 758
Fair Value Of Supply Contract [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 638 750
Asset Retirement Obligation Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 113 109
Environmental Restoration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 276 295
Under Recovered Uncollectible Accounts Expense [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 61 61
Renewable Energy Program [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 252 258
Under Recovered Energy And Transmission Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [3],[4],[5],[6],[7] 249 82
Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 44 27
Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 552 596
Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [8] 45 45
Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [9] 37 55
COPCO Acquisition Adjustment [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 5
Workers Compensation and Long-Term Disability [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 34 35
Recoverable Vacation Pay [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 30 19
Stranded Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 64 79
CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 11 8
Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 545 529
DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 179 190
Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 78 67
Under funded Benefit Post Retirement Obligation [Member] | Constellation Energy Group LLC [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 414 440
Under funded Benefit Post Retirement Obligation [Member] | Pepco Holdings LLC [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 915 953
PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 136  
Exelon Generation Co L L C [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0  
Commonwealth Edison Co [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 1,371 1,279
Current 237 225
Regulatory Assets, Noncurrent 1,134 1,054
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | Deferred Income Tax Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 147 155
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [2] 243 244
Commonwealth Edison Co [Member] | Energy Efficiency Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 284 166
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 35 37
Commonwealth Edison Co [Member] | Fair Value Of Long Term Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | Fair Value Of Supply Contract [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | Asset Retirement Obligation Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 76 73
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 257 273
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 61 61
Commonwealth Edison Co [Member] | Renewable Energy Program [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 252 256
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [5] 8 6
Commonwealth Edison Co [Member] | Storm Costs [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 0
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | COPCO Acquisition Adjustment [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] | CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Commonwealth Edison Co [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 8 8
Commonwealth Edison Co [Member] | Annual Reconciliations [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 180 186
Commonwealth Edison Co [Member] | Recoverable Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 63 58
Commonwealth Edison Co [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0  
PECO Energy Co [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 502 410
Current 75 29
Regulatory Assets, Noncurrent 427 381
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 353 297
PECO Energy Co [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 30 36
PECO Energy Co [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | Energy Efficiency 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]    
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 19 22
PECO Energy Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | Renewable Energy Program [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 37 [5] 1
PECO Energy Co [Member] | Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 1 1
PECO Energy Co [Member] | Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | COPCO Acquisition Adjustment [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 16 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 11 8
PECO Energy Co [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
PECO Energy Co [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 12 16
PECO Energy Co [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0  
Baltimore Gas and Electric Company [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 590 571
Current 185 174
Regulatory Assets, Noncurrent 405 397
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Plans Costs [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 0 0
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 203 214
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Baltimore Gas and Electric Company [Member] | Energy Efficiency 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 11 11
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] | Fair Value Of Supply Contract [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligation Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 15 14
Baltimore Gas and Electric Company [Member] | Environmental Restoration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
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 Program [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 [4] 75 23
Baltimore Gas and Electric Company [Member] | Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 267 285
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 6
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [9] 9 14
Baltimore Gas and Electric Company [Member] | COPCO Acquisition Adjustment [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
Baltimore Gas and Electric Company [Member] | CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Baltimore Gas and Electric Company [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Baltimore Gas and Electric Company [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 6 4
Baltimore Gas and Electric Company [Member] | Unamortized AMI Expenses [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 121 129
Baltimore Gas and Electric Company [Member] | Legacy AMI [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 49 53
Baltimore Gas and Electric Company [Member] | Recoverable Smart Meter Related Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 33 32
Baltimore Gas and Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 7 5
Baltimore Gas and Electric Company [Member] | TransmissionCost [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 14 7
Baltimore Gas and Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 51  
Baltimore Gas and Electric Company [Member] | Abandonment costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 3 3
Baltimore Gas and Electric Company [Member] | Under-Recovered Natural Gas Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets   8
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 9 10
Baltimore Gas and Electric Company [Member] | UnderRecoveredNaturalGasDecouplingRevenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 19 4
Pepco Holdings LLC [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 2,951 3,047
Current 512 554
Regulatory Assets, Noncurrent 2,439 2,493
Pepco Holdings LLC [Member] | Pension and Other Postretirement Plans Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Deferred Income Tax Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 10 9
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 222 235
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Energy Efficiency Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Loss on Reacquired Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 69 73
Pepco Holdings LLC [Member] | Fair Value Of Long Term Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 594 619
Pepco Holdings LLC [Member] | Fair Value Of Supply Contract [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 638 750
Pepco Holdings LLC [Member] | Asset Retirement Obligation Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Environmental Restoration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Under Recovered Uncollectible Accounts Expense [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Renewable Energy Program [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 2
Pepco Holdings LLC [Member] | Under Recovered Energy And Transmission Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [3],[6],[7] 129 52
Pepco Holdings LLC [Member] | Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 44 27
Pepco Holdings LLC [Member] | Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 284 310
Pepco Holdings LLC [Member] | Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [8],[10] 41 39
Pepco Holdings LLC [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 28 41
Pepco Holdings LLC [Member] | COPCO Acquisition Adjustment [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 5
Pepco Holdings LLC [Member] | Workers Compensation and Long-Term Disability [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 34 35
Pepco Holdings LLC [Member] | Recoverable Vacation Pay [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 14 13
Pepco Holdings LLC [Member] | Stranded Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 64 79
Pepco Holdings LLC [Member] | CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Pepco Holdings LLC [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 545 529
Pepco Holdings LLC [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 179 190
Pepco Holdings LLC [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 52 39
Pepco Holdings LLC [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 85  
Potomac Electric Power Company [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 930 891
Current 248 213
Regulatory Assets, Noncurrent 682 678
Potomac Electric Power Company [Member] | Pension and Other Postretirement Plans Costs [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 10 9
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 149 158
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Potomac Electric Power Company [Member] | Energy Efficiency Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Potomac Electric Power Company [Member] | Loss on Reacquired Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 14 15
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] | Fair Value Of Supply Contract [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 0 0
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 Program [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 [7] 90 11
Potomac Electric Power Company [Member] | Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 10 7
Potomac Electric Power Company [Member] | Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 206 229
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 19 20
Potomac Electric Power Company [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 28 38
Potomac Electric Power Company [Member] | COPCO Acquisition Adjustment [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 34 35
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] | CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Potomac Electric Power Company [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 153 150
Potomac Electric Power Company [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 179 190
Potomac Electric Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 38 29
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 2 8
Potomac Electric Power Company [Member] | TransmissionCost [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 3
Potomac Electric Power Company [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 84  
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 10 11
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInDCServiceTerritory [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 9 9
Delmarva Power and Light Company [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 306 314
Current 64 69
Regulatory Assets, Noncurrent 242 245
Delmarva Power and Light Company [Member] | Pension and Other Postretirement Plans Costs [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 0 0
Delmarva Power and Light Company [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 73 77
Delmarva Power and Light Company [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Delmarva Power and Light Company [Member] | Energy Efficiency Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Delmarva Power and Light Company [Member] | Loss on Reacquired Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 7 8
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] | Fair Value Of Supply Contract [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 Program [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 1
Delmarva Power and Light Company [Member] | Under Recovered Energy And Transmission Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [6] 14 15
Delmarva Power and Light Company [Member] | Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 5
Delmarva Power and Light Company [Member] | Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 78 81
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [10] 12 10
Delmarva Power and Light Company [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 3
Delmarva Power and Light Company [Member] | COPCO Acquisition Adjustment [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 5
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 8 8
Delmarva Power and Light Company [Member] | Stranded Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Delmarva Power and Light Company [Member] | CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Delmarva Power and Light Company [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 95 93
Delmarva Power and Light Company [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Delmarva Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 11 8
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 2 7
Delmarva Power and Light Company [Member] | TransmissionCost [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 12 8
Delmarva Power and Light Company [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0  
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4 4
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritory [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets   5
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritoryElectric [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 4  
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritoryGas [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 2  
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandAndDelawareServiceTerritories [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 2 1
Atlantic City Electric Company [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 441 430
Current 60 71
Regulatory Assets, Noncurrent 381 359
Atlantic City Electric Company [Member] | Pension and Other Postretirement Plans Costs [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 0 0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | Energy Efficiency Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | Loss on Reacquired Debt [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 5 5
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 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 Program [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 1
Atlantic City Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [3] 25 26
Atlantic City Electric Company [Member] | Storm Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 30 15
Atlantic City Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | Merger Integration Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets [8] 10 9
Atlantic City Electric Company [Member] | Under Recovered Decoupling Revenue [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | COPCO Acquisition Adjustment [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 6 5
Atlantic City Electric Company [Member] | Stranded Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 64 79
Atlantic City Electric Company [Member] | CAP Arrearage [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | Removal Costs [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 298 286
Atlantic City Electric Company [Member] | DC PLUG Charge [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 0 0
Atlantic City Electric Company [Member] | Other Regulatory Assets (Liabilities) [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 3 4
Atlantic City Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 16 15
Atlantic City Electric Company [Member] | TransmissionCost [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 8 $ 11
Atlantic City Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets $ 1  
[1] Includes regulatory assets established at the Constellation and PHI merger dates of $414 million and $915 million, respectively, as of June 30, 2018 and $440 million and $953 million, respectively, as of December 31, 2017 related to the rate regulated portions of the deferred costs associated with legacy Constellation’s and PHI’s pension and other postretirement benefit plans that are being amortized and recovered over approximately 12 years and 3 to 15 years, respectively (as established at the respective acquisition dates). The Utility Registrants are not earning or paying a return on these amounts.
[2] As of June 30, 2018, ComEd’s regulatory asset of $243 million was comprised of $180 million for the 2016, 2017 and 2018 annual reconciliations and $63 million related to significant one-time events. As of December 31, 2017, ComEd’s regulatory asset of $244 million was comprised of $186 million for the 2016 and 2017 annual reconciliations and $58 million related to significant one-time events.
[3] As of June 30, 2018, ACE's regulatory asset of $25 million included $1 million related to the PJM Transmission Rate Design Settlement, $8 million of transmission costs recoverable through its FERC approved formula rate and $16 million of under-recovered electric energy costs. As of June 30, 2018, ACE's regulatory liability of $10 million included $4 million related to the PJM Transmission Rate Design Settlement and $6 million related to over-recovered electric energy costs. As of December 31, 2017, ACE's regulatory asset of $26 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of December 31, 2017, ACE's regulatory liability of $3 million related to over-recovered electric energy costs.
[4] As of June 30, 2018, BGE's regulatory asset of $75 million included $51 million related to the PJM Transmission Rate Design Settlement, $14 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $7 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of June 30, 2018, BGE's regulatory liability of $15 million related to over-recovered natural gas costs. As of December 31, 2017, BGE’s regulatory asset of $23 million included $7 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval and $8 million of under-recovered natural gas costs.
[5] As of June 30, 2018, ComEd’s regulatory asset of $8 million represents transmission costs recoverable through its FERC approved formula rate. As of June 30, 2018, ComEd’s regulatory liability of $154 million included $99 million related to the PJM Transmission Rate Design Settlement, $23 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2017, ComEd’s regulatory asset of $6 million represents transmission costs recoverable through its FERC approved formula rate. As of December 31, 2017, ComEd’s regulatory liability of $47 million included $14 million related to over-recovered energy costs and $33 million associated with revenues received for renewable energy requirements.
[6] As of June 30, 2018, DPL's regulatory asset of $14 million included $12 million of transmission costs recoverable through its FERC approved formula rate and $2 million related to under-recovered electric energy costs. As of June 30, 2018, DPL's regulatory liability of $18 million included $10 million related to the PJM Transmission Rate Design Settlement and $8 million related to over-recovered electric energy and gas fuel costs. As of December 31, 2017, DPL's regulatory asset of $15 million included $8 million of transmission costs recoverable through its FERC approved formula rate and $7 million related to under-recovered electric energy costs. As of December 31, 2017, DPL's regulatory liability of $1 million related to over-recovered electric energy costs.
[7] As of June 30, 2018, Pepco's regulatory asset of $90 million included $84 million related to the PJM Transmission Rate Design Settlement, $4 million of transmission costs recoverable through its FERC approved formula rate and $2 million related to under-recovered electric energy costs. As of December 31, 2017, Pepco's regulatory asset of $11 million included $3 million of transmission costs recoverable through its FERC approved formula rate and $8 million of under-recovered electric energy costs.
[8] As of June 30, 2018 and December 31, 2017, ACE’s regulatory asset of $10 million and $9 million, respectively, represents previously incurred PHI integration costs expected to be recovered in the New Jersey service territory.
[9] Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of June 30, 2018, BGE had a regulatory asset of $9 million related to under-recovered electric revenue decoupling and a regulatory liability of $19 million related to over-recovered natural gas revenue decoupling. As of December 31, 2017, BGE had a regulatory asset of $10 million related to under-recovered electric revenue decoupling and $4 million related to under-recovered natural gas revenue decoupling.
[10] As of June 30, 2018, DPL’s regulatory asset of $12 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $4 million authorized for recovery in Delaware electric rates, $2 million authorized for recovery in Delaware gas rates and $2 million expected to be recovered in electric rates in the Delaware and Maryland service territories. As of June 30, 2018, DPL’s regulatory liability of $3 million represents net synergy savings incurred related to PHI integration costs that are expected to be returned in electric and gas rates in the Delaware service territory. As of December 31, 2017, DPL’s regulatory asset of $10 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, and $1 million expected to be recovered in electric and gas rates in the Maryland and Delaware service territories.