Leases Supplemental Balance Sheet Information Related to Lessee Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	$ 3,038	$ 1,575
Other current liabilities	1,367	1,035
Other deferred credits and other liabilities	3,053	2,130
Total Operating Lease Liabilities	1,603
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	1,841	755
Other current liabilities	481	279
Other deferred credits and other liabilities	1,449	610
Total Operating Lease Liabilities	1,154
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	354	395
Other current liabilities	126	96
Other deferred credits and other liabilities	592	630
Total Operating Lease Liabilities	12
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	30	27
Other current liabilities	40	24
Other deferred credits and other liabilities	79	76
Total Operating Lease Liabilities	2
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	95	5
Other current liabilities	51	27
Other deferred credits and other liabilities	128	73
Total Operating Lease Liabilities	97
Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	360	60
Other current liabilities	133	123
Other deferred credits and other liabilities	617	369
Total Operating Lease Liabilities	316
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	77	15
Other current liabilities	23	42
Other deferred credits and other liabilities	313	275
Total Operating Lease Liabilities	68
Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	80	6
Other current liabilities	16	7
Other deferred credits and other liabilities	113	50
Total Operating Lease Liabilities	83
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	60	40
Other current liabilities	10	4
Other deferred credits and other liabilities	44	$ 27
Total Operating Lease Liabilities	25
Contracted Generation [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	595
Total Operating Lease Liabilities	744
Contracted Generation [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	595
Total Operating Lease Liabilities	744
Other Deferred Debits and Other Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	1,412
Other Deferred Debits and Other Assets [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	982
Other Deferred Debits and Other Assets [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	11
Other Deferred Debits and Other Assets [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	2
Other Deferred Debits and Other Assets [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	91
Other Deferred Debits and Other Assets [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	309
Other Deferred Debits and Other Assets [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	67
Other Deferred Debits and Other Assets [Member] | Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	74
Other Deferred Debits and Other Assets [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	24
Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	250
Other Current Liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	173
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	1
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	36
Other Current Liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	8
Other Current Liabilities [Member] | Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	11
Other Current Liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	6
Other Deferred Credits and Other Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	1,353
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	981
Other Deferred Credits and Other Liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	9
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	65
Other Deferred Credits and Other Liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	280
Other Deferred Credits and Other Liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	60
Other Deferred Credits and Other Liabilities [Member] | Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	72
Other Deferred Credits and Other Liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	$ 19