Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Liability Adjustment - Noncontrolling Interest	$ (290)
Income taxes	174	$ 216	$ 229	$ 141
CENG [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Liability Adjustment - Noncontrolling Interest	290
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Liability Adjustment - Noncontrolling Interest	(288)
Income taxes	177	100	108	41
Exelon Generation Co L L C [Member] | CENG [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Liability Adjustment - Noncontrolling Interest	288
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Income taxes	(11)	$ (7)	(12)	(39)
State and Local Jurisdiction [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Deferred Income Taxes			27	66
Income taxes			27
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Deferred Income Taxes				$ (26)
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 14		$ 14