Lessee - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	$ 1,264	$ 1,331
Other deferred credits and other liabilities	2,942	3,064
Total operating lease liabilities	1,302	1,532
Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	1,064	1,305
Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	213	225
Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	1,089	1,307
Long-term Contract for Purchase of Electric Power [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	387	515
Total operating lease liabilities	528	664
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	444	517
Other deferred credits and other liabilities	1,308	1,415
Total operating lease liabilities	907	1,082
Exelon Generation Co L L C [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	726	895
Exelon Generation Co L L C [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	132	157
Exelon Generation Co L L C [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	775	925
Exelon Generation Co L L C [Member] | Long-term Contract for Purchase of Electric Power [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	387	515
Total operating lease liabilities	528	664	$ 493
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	143	122
Other deferred credits and other liabilities	595	635
Total operating lease liabilities	8	11
Commonwealth Edison Co [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	7	9
Commonwealth Edison Co [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	3	3
Commonwealth Edison Co [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	5	8
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	30	19
Other deferred credits and other liabilities	93	74
Total operating lease liabilities	1	1
PECO Energy Co [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	1	2
PECO Energy Co [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	0	0
PECO Energy Co [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	1	1
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	91	63
Other deferred credits and other liabilities	104	116
Total operating lease liabilities	64	82
Baltimore Gas and Electric Company [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	46	77
Baltimore Gas and Electric Company [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	45	32
Baltimore Gas and Electric Company [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	19	50
Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	141	131
Other deferred credits and other liabilities	622	577
Total operating lease liabilities	255	285
Finance Lease, Liability, Current	7
Finance Lease, Liability, Noncurrent	43
Finance lease, liability	50
Pepco Holdings LLC [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	241	273
Pepco Holdings LLC [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	31	31
Pepco Holdings LLC [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	224	254
Pepco Holdings LLC [Member] | Property, Plant and Equipment
Supplemental Balance Sheet Information [Line Items]
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	50
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	31	22
Other deferred credits and other liabilities	340	297
Total operating lease liabilities	52	57
Finance Lease, Liability, Current	2
Finance Lease, Liability, Noncurrent	15
Finance lease, liability	17
Potomac Electric Power Company [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	49	56
Potomac Electric Power Company [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	6	6
Potomac Electric Power Company [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	46	51
Potomac Electric Power Company [Member] | Property, Plant and Equipment
Supplemental Balance Sheet Information [Line Items]
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	17
Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	20	15
Other deferred credits and other liabilities	97	92
Total operating lease liabilities	65	74
Finance Lease, Liability, Current	3
Finance Lease, Liability, Noncurrent	17
Finance lease, liability	20
Delmarva Power & Light Company [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	54	63
Delmarva Power & Light Company [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	9	9
Delmarva Power & Light Company [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	56	65
Delmarva Power & Light Company [Member] | Property, Plant and Equipment
Supplemental Balance Sheet Information [Line Items]
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	20
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	11	9
Other deferred credits and other liabilities	48	39
Total operating lease liabilities	15	18
Finance Lease, Liability, Current	2
Finance Lease, Liability, Noncurrent	11
Finance lease, liability	13
Atlantic City Electric Company [Member] | Other Noncurrent Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Operating Lease, Right-of-Use Asset	15	18
Atlantic City Electric Company [Member] | Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	4	4
Atlantic City Electric Company [Member] | Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	11	$ 14
Atlantic City Electric Company [Member] | Property, Plant and Equipment
Supplemental Balance Sheet Information [Line Items]
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	$ 13