Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 10,392	$ 10,203
Regulatory Liability, Current	406	644
Noncurrent regulatory liabilities	9,986	9,559
Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4,944	5,228
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,102	2,606
Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,621	1,547
Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	109	294
Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	34
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	582	528
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,742	6,343
Regulatory Liability, Current	200	293
Noncurrent regulatory liabilities	6,542	6,050
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,297	2,394
Commonwealth Edison Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,622	2,217
Commonwealth Edison Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,435	1,368
Commonwealth Edison Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	45	137
Commonwealth Edison Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6
Commonwealth Edison Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	337	227
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	601	596
Regulatory Liability, Current	91	175
Noncurrent regulatory liabilities	510	421
PECO Energy Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	480	389
PECO Energy Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	56	132
PECO Energy Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	28
PECO Energy Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	37	75
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,228	1,269
Regulatory Liability, Current	33	77
Noncurrent regulatory liabilities	1,195	1,192
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,089	1,132
Baltimore Gas and Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	58	52
Baltimore Gas and Electric Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	6
Baltimore Gas and Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	81	79
Pepco Holdings LLC [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,777	1,948
Regulatory Liability, Current	70	84
Noncurrent regulatory liabilities	1,707	1,864
Pepco Holdings LLC [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,558	1,702
Pepco Holdings LLC [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	128	127
Pepco Holdings LLC [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	19
Pepco Holdings LLC [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	83	100
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	754	829
Regulatory Liability, Current	8	7
Noncurrent regulatory liabilities	746	822
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	725	798
Potomac Electric Power Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	20
Potomac Electric Power Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	11
Delmarva Power & Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	611	665
Regulatory Liability, Current	37	59
Noncurrent regulatory liabilities	574	606
Delmarva Power & Light Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	477	510
Delmarva Power & Light Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power & Light Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	108	107
Delmarva Power & Light Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	18
Delmarva Power & Light Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power & Light Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18	30
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	382	420
Regulatory Liability, Current	25	18
Noncurrent regulatory liabilities	357	402
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	356	394
Atlantic City Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	1
Atlantic City Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 26	$ 25