Nuclear Decommissioning - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	$ 14,688	$ 14,464
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	14,688	14,464
Assets, Total [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	14,927	14,599
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	14,927	14,599
Other Current Assets [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	239	134
Other Current Assets [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	$ 239	$ 134