Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Assets	$ 9,505	$ 9,427
Current regulatory assets	1,170	1,190
Noncurrent regulatory assets	8,335	8,237
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2,784	2,553
Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,138	1,266
Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	528	414
Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	207	234
Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	276	328
Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	34	158
Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	66	81
Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	746	472
Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	650	702
Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	443	561
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	127	118
MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	302	326
Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	301	249
Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	110	193
Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	11	41
Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	572	545
Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	32	42
Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	37	27
Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	37	50
Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	641	564
DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	126	159
Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		41
Other
Regulatory Assets [Line Items]
Regulatory Assets	337	303
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,761	1,600
Current regulatory assets	281	293
Noncurrent regulatory assets	1,480	1,307
Commonwealth Edison Co [Member] \| Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	113	136
Commonwealth Edison Co [Member] \| Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	34	158
Commonwealth Edison Co [Member] \| Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	66	81
Commonwealth Edison Co [Member] \| Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	746	472
Commonwealth Edison Co [Member] \| Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	85	79
Commonwealth Edison Co [Member] \| MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	287	309
Commonwealth Edison Co [Member] \| Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	301	249
Commonwealth Edison Co [Member] \| Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	6
Commonwealth Edison Co [Member] \| Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] \| Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] \| Other
Regulatory Assets [Line Items]
Regulatory Assets	129	110
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets	595	541
Current regulatory assets	41	81
Noncurrent regulatory assets	554	460
PECO Energy Co [Member] \| Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	518	404
PECO Energy Co [Member] \| Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	12	24
PECO Energy Co [Member] \| Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	23	22
PECO Energy Co [Member] \| MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	11	17
PECO Energy Co [Member] \| Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	6	49
PECO Energy Co [Member] \| Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	1
PECO Energy Co [Member] \| Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] \| Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] \| Other
Regulatory Assets [Line Items]
Regulatory Assets	25	24
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	637	575
Current regulatory assets	183	177
Noncurrent regulatory assets	454	398
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] \| Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	129	145
Baltimore Gas and Electric Company [Member] \| Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	45	48
Baltimore Gas and Electric Company [Member] \| Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	16	16
Baltimore Gas and Electric Company [Member] \| MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	4	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] \| Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	36	51
Baltimore Gas and Electric Company [Member] \| Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1	4
Baltimore Gas and Electric Company [Member] \| Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	303	289
Baltimore Gas and Electric Company [Member] \| Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	2	3
Baltimore Gas and Electric Company [Member] \| Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	8	2
Baltimore Gas and Electric Company [Member] \| Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	67	0
Baltimore Gas and Electric Company [Member] \| DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] \| Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Baltimore Gas and Electric Company [Member] \| Other
Regulatory Assets [Line Items]
Regulatory Assets	26	17
Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2,473	2,769
Current regulatory assets	412	457
Noncurrent regulatory assets	2,061	2,312
Pepco Holdings LLC [Member] \| Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	10	10
Pepco Holdings LLC [Member] \| Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	78	89
Pepco Holdings LLC [Member] \| Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	106	120
Pepco Holdings LLC [Member] \| Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	523	569
Pepco Holdings LLC [Member] \| Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	443	561
Pepco Holdings LLC [Member] \| Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	3	1
Pepco Holdings LLC [Member] \| MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] \| Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	68	93
Pepco Holdings LLC [Member] \| Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	10	31
Pepco Holdings LLC [Member] \| Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	269	255
Pepco Holdings LLC [Member] \| Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	30	39
Pepco Holdings LLC [Member] \| Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	29	25
Pepco Holdings LLC [Member] \| Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	37	50
Pepco Holdings LLC [Member] \| Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	574	564
Pepco Holdings LLC [Member] \| DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	126	159
Pepco Holdings LLC [Member] \| Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		41
Pepco Holdings LLC [Member] \| Other
Regulatory Assets [Line Items]
Regulatory Assets	167	162
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	772	881
Current regulatory assets	188	238
Noncurrent regulatory assets	584	643
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] \| Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	10	10
Potomac Electric Power Company [Member] \| Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	43	50
Potomac Electric Power Company [Member] \| Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	79	90
Potomac Electric Power Company [Member] \| Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	2	1
Potomac Electric Power Company [Member] \| MGP remediation costs
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] \| Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	43	84
Potomac Electric Power Company [Member] \| Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1	10
Potomac Electric Power Company [Member] \| Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	196	188
Potomac Electric Power Company [Member] \| Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	15	18
Potomac Electric Power Company [Member] \| Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	29	25
Potomac Electric Power Company [Member] \| Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] \| Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	152	158
Potomac Electric Power Company [Member] \| DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	126	159
Potomac Electric Power Company [Member] \| Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9
Potomac Electric Power Company [Member] \| Other
Regulatory Assets [Line Items]
Regulatory Assets	76	79
Delmarva Power & Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	274	290
Current regulatory assets	52	59
Noncurrent regulatory assets	222	231
Delmarva Power & Light Company [Member] \| Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	35	39
Delmarva Power & Light Company [Member] \| Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	27	30
Delmarva Power & Light Company [Member] \| Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] \| Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	5	0
Delmarva Power & Light Company [Member] \| Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2	14
Delmarva Power & Light Company [Member] \| Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	73	67
Delmarva Power & Light Company [Member] \| Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	8	11
Delmarva Power & Light Company [Member] \| Under-recovered revenue decoupling

Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($)
$ in Millions

Dec. 31, 2019

Dec. 31, 2018

Regulatory Assets [Line Items]

Regulatory Assets

$ 9,505

$ 9,427

Current regulatory assets

1,170

1,190

Noncurrent regulatory assets

8,335