Nuclear Decommissioning - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	$ 13,432	$ 13,190
Nuclear Decommissioning [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	806
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	13,432	13,190
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	806
Other Current Assets [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	115	163
Other Current Assets [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	115	163
Assets, Total [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	13,547	13,353
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	$ 13,547	$ 13,353