Nuclear Decommissioning - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	$ 15,400	$ 14,464
Nuclear Decommissioning [Member] | Minimum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	650
Nuclear Decommissioning [Member] | Maximum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	850
Nuclear Decommissioning Byron
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Related Activities Not Contractually Offset	53
Nuclear Decommissioning Byron | Minimum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	275
Nuclear Decommissioning Byron | Maximum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	375
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	15,400	14,464
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member] | Minimum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	650
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member] | Maximum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	850
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Byron
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Related Activities Not Contractually Offset	53
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Byron | Minimum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	275
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Byron | Maximum [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Net increase (decrease) due to changes in, and timing of, estimated future cash flows	375
Assets, Total [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	15,596	14,599
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	15,596	14,599
Other Current Assets [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	196	134
Other Current Assets [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Nuclear decommissioning trust funds	$ 196	$ 134