Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 10,203	$ 10,388
Regulatory Liability, Current	644	523
Noncurrent regulatory liabilities	9,559	9,865
Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5,228	5,241
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,606	3,064
Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,547	1,573
Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	294	111
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	528	399
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,343	6,577
Regulatory Liability, Current	293	249
Noncurrent regulatory liabilities	6,050	6,328
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,394	2,479
Commonwealth Edison Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,217	2,528
Commonwealth Edison Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,368	1,338
Commonwealth Edison Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	137	47
Commonwealth Edison Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	227	185
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	596	690
Regulatory Liability, Current	175	141
Noncurrent regulatory liabilities	421	549
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	389	536
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	132	60
PECO Energy Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	75	94
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,269	1,163
Regulatory Liability, Current	77	62
Noncurrent regulatory liabilities	1,192	1,101
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,132	1,032
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	52	105
Baltimore Gas and Electric Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	79	26
Pepco Holdings LLC [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,948	1,928
Regulatory Liability, Current	84	56
Noncurrent regulatory liabilities	1,864	1,872
Pepco Holdings LLC [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,702	1,730
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	127	130
Pepco Holdings LLC [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	19	4
Pepco Holdings LLC [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	100	64
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	829	832
Regulatory Liability, Current	7	3
Noncurrent regulatory liabilities	822	829
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	798	809
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] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	11	3
Delmarva Power & Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	665	635
Regulatory Liability, Current	59	42
Noncurrent regulatory liabilities	606	593
Delmarva Power & Light Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	510	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	107	110
Delmarva Power & Light Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18	1
Delmarva Power & Light Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	30	14
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	420	422
Regulatory Liability, Current	18	11
Noncurrent regulatory liabilities	402	411
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	394	411
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	1	3
Atlantic City Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 25	$ 8