Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions		Sep. 30, 2017		Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory Assets		$ 11,502		$ 11,388
Current		1,264		1,342
Regulatory Assets, Noncurrent		10,238		10,046
Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	4,020		4,162
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,423		2,016
AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		660		701
Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		256		188
Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		78
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		120		124
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		773		812
Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		830		1,085
Employee Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2		5
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		108		111
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		300		305
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		70		56
Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		277		260
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		65		89
Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		31		36
Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		10
Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets				7
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		599		621
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		47		25
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		72		27
Deferred Project Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6		8
Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33		34
Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		38		31
Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		93		138
CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9		11
AssetRemovalCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		518		477
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71		49
Under funded Benefit Post Retirement Obligation [Member]
Regulatory Assets [Line Items]
Regulatory Assets		969		995
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,574		1,167
Current		187		190
Regulatory Assets, Noncurrent		1,387		977
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	[2]	347		75
Commonwealth Edison Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		159		164
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	256		188
Commonwealth Edison Co [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		78
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		38		42
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] | 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		73		76
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		277		278
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		60		56
Commonwealth Edison Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		277		258
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4]	3		23
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
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] | 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] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6		7
Commonwealth Edison Co [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Assets [Line Items]
Regulatory Assets		73		22
Commonwealth Edison Co [Member] | Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		200		134
Commonwealth Edison Co [Member] | Recoverable Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		56		54
Commonwealth Edison Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11		20
Commonwealth Edison Co [Member] | Constellation and PHI Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		11
Commonwealth Edison Co [Member] | 561710 Exterminating and Pest Control Services [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		32		23
Commonwealth Edison Co [Member] | Constellation Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets				8
Commonwealth Edison Co [Member] | ElectricTransmissionCostsUnderRecovery [Member]
Regulatory Assets [Line Items]
Regulatory Assets				15
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,809		1,710
Current		36		29
Regulatory Assets, Noncurrent		1,773		1,681
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		1,678		1,583
PECO Energy Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		40		49
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]
Regulatory Assets		0		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		23
PECO Energy Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		23		26
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	[5]	0		0
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
PECO Energy Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets				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
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		14		7
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		9		11
PECO Energy Co [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		21		9
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		705		712
Current		208		208
Regulatory Assets, Noncurrent		497		504
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	[2]	100		98
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		219		230
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		12		7
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
Baltimore Gas and Electric Company [Member] | Employee Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2		5
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		13		12
Baltimore Gas and Electric Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		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	[6]	26		38
Baltimore Gas and Electric Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		1
Baltimore Gas and Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		10
Baltimore Gas and Electric Company [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets				7
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		284		285
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[7]	7		10
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[8]	34		3
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
Baltimore Gas and Electric Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		5
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Assets [Line Items]
Regulatory Assets		42		38
Baltimore Gas and Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		28
Baltimore Gas and Electric Company [Member] | Under-Recovered Natural Gas Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		14		3
Baltimore Gas and Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		4
Baltimore Gas and Electric Company [Member] | Abandonment costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4		3
Baltimore Gas and Electric Company [Member] | PHI Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		6
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]
Regulatory Assets [Line Items]
Regulatory Assets		24		1
Baltimore Gas and Electric Company [Member] | UnderRecoveredNaturalGasDecouplingRevenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		2
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3,260		3,504
Current		568		653
Regulatory Assets, Noncurrent		2,692		2,851
Pepco Holdings LLC [Member] | Other Postretirement Benefits [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Pepco Holdings LLC [Member] | Deferred Income Tax Charge [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		298		260
Pepco Holdings LLC [Member] | AMI Expenses [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		242		258
Pepco Holdings LLC [Member] | Under Recovered Distribution Service Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Pepco Holdings LLC [Member] | Loss on Reacquired Debt [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		75		81
Pepco Holdings LLC [Member] | Fair Value Of Long Term Debt [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		632		671
Pepco Holdings LLC [Member] | Fair Value Of Supply Contract [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		830		1,085
Pepco Holdings LLC [Member] | Employee Severance [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Pepco Holdings LLC [Member] | Asset Retirement Obligation Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Pepco Holdings LLC [Member] | Environmental Restoration Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Pepco Holdings LLC [Member] | Under Recovered Uncollectible Accounts Expense [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		0
Pepco Holdings LLC [Member] | Renewable Energy And Associated REC [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		2
Pepco Holdings LLC [Member] | Under Recovered Energy And Transmission Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		28
Pepco Holdings LLC [Member] | Deferred Storm Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		31		35
Pepco Holdings LLC [Member] | Electric Generation Related Regulatory Asset [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Pepco Holdings LLC [Member] | Rate Stabilization Deferral [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets				0
Pepco Holdings LLC [Member] | Energy Efficiency And Demand Response Programs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		314		335
Pepco Holdings LLC [Member] | Merger Integration Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		40		15
Pepco Holdings LLC [Member] | Under Recovered Decoupling Revenue [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		38		24
Pepco Holdings LLC [Member] | Deferred Project Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6		8
Pepco Holdings LLC [Member] | Workers Compensation and Long-Term Disability [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33		34
Pepco Holdings LLC [Member] | Recoverable Vacation Pay [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		24		24
Pepco Holdings LLC [Member] | Stranded Costs [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		93		138
Pepco Holdings LLC [Member] | AssetRemovalCosts [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		518		477
Pepco Holdings LLC [Member] | Other Regulatory Assets (Liabilities) [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		40		29
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		880		852
Current		181		162
Regulatory Assets, Noncurrent		699		690
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	[2]	195		171
Potomac Electric Power Company [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		163		174
Potomac Electric Power Company [Member] | Under Recovered Distribution Service 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		16		17
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
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		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 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	[9]	6		6
Potomac Electric Power Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9		12
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				0
Potomac Electric Power Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		233		250
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[10]	20		11
Potomac Electric Power Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33		21
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		33		34
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		144		134
Potomac Electric Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		28		22
Potomac Electric Power Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Assets [Line Items]
Regulatory Assets		34		31
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		6
Potomac Electric Power Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3
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	[10]	9
Delmarva Power and Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		369		348
Current		69		59
Regulatory Assets, Noncurrent		300		289
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	[2]	45		38
Delmarva Power and Light Company [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		79		84
Delmarva Power and Light Company [Member] | Under Recovered Distribution Service 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		8		9
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
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	[11]	9		5
Delmarva Power and Light Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		5
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				0
Delmarva Power and Light Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		81		85
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[10]	11		4
Delmarva Power and Light Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		3
Delmarva Power and Light Company [Member] | Deferred Project Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6		8
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		14		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		98		88
Delmarva Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		8		5
Delmarva Power and Light Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Assets [Line Items]
Regulatory Assets		23		20
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		4
Delmarva Power and Light Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4		1
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		504		501
Current		87		96
Regulatory Assets, Noncurrent		417		405
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	[2]	58		51
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		0
Atlantic City Electric Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		6
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] | 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		10		0
Atlantic City Electric Company [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		2
Atlantic City Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	21	[11]	17
Atlantic City Electric Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		17		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
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		9		0
Atlantic City Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		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		10		10
Atlantic City Electric Company [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		93		138
Atlantic City Electric Company [Member] | AssetRemovalCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		277		255
Atlantic City Electric Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4		4
Atlantic City Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Assets [Line Items]
Regulatory Assets		21		19
Atlantic City Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		11
Atlantic City Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11		$ 6
Electric Distribution [Member] | Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 2

[1] As of September 30, 2017 and December 31, 2016, the pension and other postretirement benefits regulatory asset at Exelon includes regulatory assets of $969 million and $995 million, respectively, as a result of the PHI Merger related to unrecognized costs that are probable of regulatory recovery. The regulatory assets are amortized over periods from 3 to 15 years, depending on the underlying component. Pepco, DPL and ACE are currently recovering these costs through base rates. Pepco, DPL and ACE are not earning a return on the recovery of these costs in base rates.

[2] As of September 30, 2017, includes transmission-related income tax regulatory assets that require FERC approval separate from the transmission formula rate of $73 million, $42 million, $34 million, $23 million and $21 million for ComEd, BGE, Pepco, DPL and ACE, respectively. As of December 31, 2016, includes transmission-related regulatory assets that require FERC approval separate from the transmission formula rate of $22 million, $38 million, $31 million, $20 million and $19 million for ComEd, BGE, Pepco, DPL and ACE, respectively. On December 13, 2016, BGE filed with FERC to begin recovering these existing and any similar future regulatory assets through its transmission formula rate. On May 9, 2017, FERC accepted BGE’s filing and made effective BGE’s proposed modifications to its transmission formula rate, subject to refund and further Commission order. ComEd, Pepco, DPL, and ACE are expected to make similar filings with FERC and other parties in subsequent periods.

[3] As of September 30, 2017, ComEd’s regulatory asset of $256 million was comprised of $200 million for the 2015 - 2017 annual reconciliations and $56 million related to significant one-time events including $11 million of deferred storm costs, $7 million of Constellation and PHI merger and integration related costs, $6 million of emerald ash borer costs, and $32 million of smart meter related costs. As of December 31, 2016, ComEd’s regulatory asset of $188 million was comprised of $134 million for the 2015 and 2016 annual reconciliations and $54 million related to significant one-time events, including $20 million of deferred storm costs and $11 million of Constellation and PHI merger and integration related costs, and $23 million of smart meter related costs. See Note 4— Mergers, Acquisitions and Dispositions of the Exelon 2016 Form 10-K for further information.

[4] As of September 30, 2017, ComEd’s regulatory liability of $54 million included $22 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2016, ComEd’s regulatory asset of $23 million included $15 million associated with transmission costs recoverable through its FERC approved formula rate and $8 million of Constellation merger and integration costs to be recovered upon FERC approval. As of December 31, 2016, ComEd’s regulatory liability of $60 million included $30 million related to over-recovered energy costs and $30 million associated with revenues received for renewable energy requirements.

[5] As of September 30, 2017, PECO's regulatory liability of $68 million included $34 million related to over-recovered costs under the DSP program, $21 million related to the over-recovered natural gas costs under the PGC and $13 million related to over-recovered non-bypassable transmission service charges. As of December 31, 2016, PECO's regulatory liability of $56 million included $34 million related to over-recovered costs under the DSP program, $10 million related to over-recovered non-bypassable transmission service charges, $8 million related to the over-recovered natural gas costs under the PGC and $4 million related to the over-recovered electric transmission costs.

[6] As of September 30, 2017, BGE's regulatory asset of $26 million included $5 million related to under-recovered electric energy costs, $14 million related to under-recovered natural gas costs, $3 million of costs associated with transmission costs recoverable through its FERC approved formula rate and $4 million of abandonment costs to be recovered upon FERC approval. As of December 31, 2016, BGE’s regulatory asset of $38 million included $4 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $28 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval, and $3 million of under-recovered natural gas costs.

[7] As of September 30, 2017 and December 31, 2016, BGE's regulatory asset of $7 million and $10 million, respectively, included $5 million and $6 million, respectively, of previously incurred PHI acquisition costs as authorized by the June 2016 rate case order.

[8] Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of September 30, 2017, BGE had a regulatory asset of $24 million related to under-recovered electric revenue decoupling and $10 million related to under-recovered natural gas revenue decoupling. As of December 31, 2016, BGE had a regulatory asset of $2 million related to under-recovered natural gas revenue decoupling and $1 million related to under-recovered electric revenue decoupling.

[9] As of September 30, 2017, Pepco's regulatory asset of $6 million included $3 million of transmission costs recoverable through its FERC approved formula rate and $3 million of under-recovered electric energy costs. As of September 30, 2017, Pepco's regulatory liability of $3 million related to over-recovered electric energy costs. As of December 31, 2016, Pepco's regulatory asset of $6 million related to under-recovered electric energy costs. As of December 31, 2016, Pepco's regulatory liability of $8 million included $5 million of over-recovered transmission costs and $3 million of over-recovered electric energy costs.

[10] As of September 30, 2017, Pepco’s regulatory asset of $20 million represents previously incurred PHI acquisition costs, including $11 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. As of December 31, 2016, Pepco's regulatory asset of $11 million represents previously incurred PHI acquisition costs authorized for recovery in Maryland. (l)As of September 30, 2017, DPL’s regulatory asset of $11 million represents previously incurred PHI acquisition costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, and $2 million expected to be recovered in electric and gas rates in the Delaware service territory. As of December 31, 2016, DPL's regulatory asset of $4 million represents previously incurred PHI acquisition costs expected to be recovered in the Maryland service territory.

[11] As of September 30, 2017, DPL's regulatory asset of $9 million included $4 million of transmission costs recoverable through its FERC approved formula rate and $5 million related to under-recovered electric energy costs. As of September 30, 2017, DPL's regulatory liability of $9 million related to over-recovered electric energy costs. As of December 31, 2016, DPL's regulatory asset of $5 million included $1 million of transmission costs recoverable through its FERC approved formula rate and $4 million of under-recovered electric energy costs. As of December 31, 2016, DPL's regulatory liability of $5 million included $2 million of over-recovered electric energy costs and $3 million of over-recovered transmission costs.

[12] As of September 30, 2017, ACE's regulatory asset of $21 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $10 million of under-recovered electric energy costs. As of September 30, 2017, ACE's regulatory liability of $5 million related to over-recovered electric energy costs. As of December 31, 2016, ACE's regulatory asset of $17 million included $6 million of transmission costs recoverable through its FERC approved formula rate and $11 million of under-recovered electric energy costs. As of December 31, 2016, ACE's regulatory liability of $5 million included $4 million of over-recovered transmission costs and $1 million of over-recovered electric energy costs.