Leases Supplemental Balance Sheet Information Related to Lessee Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		$ 3,017	$ 1,575
Other current liabilities		1,245	1,035
Other deferred credits and other liabilities		3,158	2,130
Total Operating Lease Liabilities	[1]	1,644
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		1,813	755
Other current liabilities		425	279
Other deferred credits and other liabilities		1,528	610
Total Operating Lease Liabilities	[1]	1,196
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		347	395
Other current liabilities		98	96
Other deferred credits and other liabilities		582	630
Total Operating Lease Liabilities		7
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		29	27
Other current liabilities		32	24
Other deferred credits and other liabilities		81	76
Total Operating Lease Liabilities		2
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		105	5
Other current liabilities		54	27
Other deferred credits and other liabilities		130	73
Total Operating Lease Liabilities		97
Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		370	60
Other current liabilities		127	123
Other deferred credits and other liabilities		630	369
Total Operating Lease Liabilities		320
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		80	15
Other current liabilities		17	42
Other deferred credits and other liabilities		360	312
Total Operating Lease Liabilities		68
Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		81	6
Other current liabilities		16	7
Other deferred credits and other liabilities		114	50
Total Operating Lease Liabilities		83
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		64	40
Other current liabilities		10	4
Other deferred credits and other liabilities		46	$ 27
Total Operating Lease Liabilities		26
Contracted Generation [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		631
Total Operating Lease Liabilities		778
Contracted Generation [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		631
Total Operating Lease Liabilities		778
Other Deferred Debits and Other Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	[1]	1,465
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	[1]	1,027
Other Deferred Debits and Other Assets [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		5
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		97
Other Deferred Debits and Other Assets [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		314
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		75
Other Deferred Debits and Other Assets [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		26
Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	[1]	249
Other Current Liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	[1]	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		31
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]	1,395
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	[1]	1,023
Other Deferred Credits and Other Liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		4
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		66
Other Deferred Credits and Other Liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		284
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		$ 20

[1] Exelon's and Generation's operating ROU assets and lease liabilities include $631 million and $778 million, respectively, related to contracted generation.