Lessee - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	$ 3,197	$ 1,575
Other current liabilities	1,331	1,035
Other deferred credits and other liabilities	3,064	2,130
Total operating lease liabilities	1,532
Long-term Contract for Purchase of Electric Power [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	515
Total operating lease liabilities	664
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	1,960	755
Other current liabilities	517	279
Other deferred credits and other liabilities	1,415	610
Total operating lease liabilities	1,082
Exelon Generation Co L L C [Member] | Long-term Contract for Purchase of Electric Power [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	515
Total operating lease liabilities	664	493	$ 508
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	347	395
Other current liabilities	122	96
Other deferred credits and other liabilities	635	630
Total operating lease liabilities	11
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	29	27
Other current liabilities	19	24
Other deferred credits and other liabilities	74	76
Total operating lease liabilities	1
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	86	5
Other current liabilities	63	27
Other deferred credits and other liabilities	116	73
Total operating lease liabilities	82
Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	323	60
Other current liabilities	131	123
Other deferred credits and other liabilities	577	369
Total operating lease liabilities	285
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	66	15
Other current liabilities	22	42
Other deferred credits and other liabilities	297	275
Total operating lease liabilities	57
Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	69	6
Other current liabilities	15	7
Other deferred credits and other liabilities	104	50
Total operating lease liabilities	74
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	53	40
Other current liabilities	9	4
Other deferred credits and other liabilities	39	$ 27
Total operating lease liabilities	18
Other deferred debits and other assets [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	1,305
Other deferred debits and other assets [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	895
Other deferred debits and other assets [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	9
Other deferred debits and other assets [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	2
Other deferred debits and other assets [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	77
Other deferred debits and other assets [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	273
Other deferred debits and other assets [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	56
Other deferred debits and other assets [Member] | Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	63
Other deferred debits and other assets [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	18
Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	225
Other Current Liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	157
Other Current Liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	3
Other Current Liabilities [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	0
Other Current Liabilities [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	32
Other Current Liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	31
Other Current Liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	6
Other Current Liabilities [Member] | Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	9
Other Current Liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	4
Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	1,307
Other deferred credits and other liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	925
Other deferred credits and other liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	8
Other deferred credits and other liabilities [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	1
Other deferred credits and other liabilities [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	50
Other deferred credits and other liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	254
Other deferred credits and other liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	51
Other deferred credits and other liabilities [Member] | Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	65
Other deferred credits and other liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	$ 14