Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions		Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory Assets		$ 9,342		$ 9,288
Current		1,340		1,267
Regulatory Assets, Noncurrent		8,002		8,021
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	3,710		3,848
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		391		306
Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	583		640
Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	228		244
Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		357		166
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		102		116
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		716		758
Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		600		750
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		114		109
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		318		295
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71		61
Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		260		258
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8]	251		82
Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		45		27
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		561		596
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	44		45
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	64		55
COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		5
Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		35
Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		24		19
Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		57		79
CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		8
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		555		529
DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		168		190
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		74		67
Under funded Benefit Post Retirement Obligation [Member] | Constellation Energy Group LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		401		440
Under funded Benefit Post Retirement Obligation [Member] | Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		897		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		1,485		1,279
Current		256		225
Regulatory Assets, Noncurrent		1,229		1,054
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	142		155
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	228		244
Commonwealth Edison Co [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		357		166
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		34		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		299		273
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71		61
Commonwealth Edison Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		259		256
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8]	7		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	[9],[10],[11]	0		0
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	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		12		8
Commonwealth Edison Co [Member] | Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		165		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		532		410
Current		84		29
Regulatory Assets, Noncurrent		448		381
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	0		0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		381		297
PECO Energy Co [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	27		36
PECO Energy Co [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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	[4],[5],[6],[7],[8]	50		1
PECO Energy Co [Member] | Under Recovered Electric Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[6]	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		2		1
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	0		0
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	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		11		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		10		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		9		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		597		571
Current		195		174
Regulatory Assets, Noncurrent		402		397
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	198		214
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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],[5],[6],[7],[8]	72		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		291		285
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	4		6
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	0		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		117		129
Baltimore Gas and Electric Company [Member] | Legacy AMI [Member]
Regulatory Assets [Line Items]
Regulatory Assets		48		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		48	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		1		10
Baltimore Gas and Electric Company [Member] | UnderRecoveredNaturalGasDecouplingRevenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		17		4
Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,895		3,047
Current		521		554
Regulatory Assets, Noncurrent		2,374		2,493
Pepco Holdings LLC [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	216		235
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		68		73
Pepco Holdings LLC [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		581		619
Pepco Holdings LLC [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		600		750
Pepco Holdings LLC [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1		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		1		2
Pepco Holdings LLC [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8]	122		52
Pepco Holdings LLC [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		45		27
Pepco Holdings LLC [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		268		310
Pepco Holdings LLC [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	40		39
Pepco Holdings LLC [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	64		41
Pepco Holdings LLC [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		5
Pepco Holdings LLC [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		35
Pepco Holdings LLC [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		13		13
Pepco Holdings LLC [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		57		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		555		529
Pepco Holdings LLC [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		168		190
Pepco Holdings LLC [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		47		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		946		891
Current		284		213
Regulatory Assets, Noncurrent		662		678
Potomac Electric Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	144		158
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		15		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		1		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	[4],[5],[6],[7],[8]	93		11
Potomac Electric Power Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11		7
Potomac Electric Power Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		194		229
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	18		20
Potomac Electric Power Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	64		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		36		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		156		150
Potomac Electric Power Company [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		168		190
Potomac Electric Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		29
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		12		8
Potomac Electric Power Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		3
Potomac Electric Power Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets		74	84
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9		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		301		314
Current		66		69
Regulatory Assets, Noncurrent		235		245
Delmarva Power and Light Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	72		77
Delmarva Power and Light Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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	[4],[5],[6],[7],[8]	15		15
Delmarva Power and Light Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5		5
Delmarva Power and Light Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		74		81
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	12		10
Delmarva Power and Light Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	0		3
Delmarva Power and Light Company [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		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		97		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		8		8
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1		7
Delmarva Power and Light Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		14		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		5
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		1		1
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		427		430
Current		44		71
Regulatory Assets, Noncurrent		383		359
Atlantic City Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	0		0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		6		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		1		1
Atlantic City Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8]	14		26
Atlantic City Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		29		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	[9],[10],[11]	10		9
Atlantic City Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	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		5		5
Atlantic City Electric Company [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		57		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		302		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		7		15
Atlantic City Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 7		$ 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 $401 million and $897 million, respectively, as of September 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 September 30, 2018, BGE's regulatory asset of $198 million includes $117 million of unamortized incremental deployment costs under the program, $48 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $33 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. As of December 31, 2017, BGE's regulatory asset of $214 million includes $129 million of unamortized incremental deployment costs under the program, $53 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. Recovery of the post-test year incremental deployment costs will be addressed in a future base rate proceeding.

[3] As of September 30, 2018, ComEd’s regulatory asset of $228 million was comprised of $165 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.

[4] As of September 30, 2018, ACE's regulatory asset of $14 million included $7 million of transmission costs recoverable through its FERC approved formula rate and $7 million of under-recovered electric energy costs. As of September 30, 2018, ACE's regulatory liability of $4 million included $3 million related to the PJM Transmission Rate Design Settlement and $1 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.

[5] As of September 30, 2018, BGE's regulatory asset of $72 million included $48 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 September 30, 2018, BGE's regulatory liability of $7 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.

[6] As of September 30, 2018, ComEd’s regulatory asset of $7 million represents transmission costs recoverable through its FERC approved formula rate. As of September 30, 2018, ComEd’s regulatory liability of $204 million included $101 million related to the PJM Transmission Rate Design Settlement, $72 million related to over-recovered energy costs and $31 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.

[7] As of September 30, 2018, DPL's regulatory asset of $15 million included $14 million of transmission costs recoverable through its FERC approved formula rate and $1 million related to under-recovered electric energy costs. As of September 30, 2018, DPL's regulatory liability of $14 million included $10 million related to the PJM Transmission Rate Design Settlement and $4 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.

[8] As of September 30, 2018, Pepco's regulatory asset of $93 million included $74 million related to the PJM Transmission Rate Design Settlement, $7 million of transmission costs recoverable through its FERC approved formula rate and $12 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.

[9] As of September 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.

[10] As of September 30, 2018, DPL’s regulatory asset of $12 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, $2 million authorized for recovery in Delaware gas rates and $1 million expected to be recovered in electric rates in the Delaware and Maryland service territories. As of September 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.

[11] As of September 30, 2018, Pepco’s regulatory asset of $18 million represents previously incurred PHI integration costs, including $9 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. As of December 31, 2017, Pepco’s regulatory asset of $20 million represents previously incurred PHI integration costs, including $11 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory.

[12] Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of September 30, 2018, BGE had a regulatory asset of less than $1 million related to under-recovered electric revenue decoupling and a regulatory liability of $17 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.