Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	$ 1,443	$ 1,425
Property, plant and equipment, net	82,120	82,584
Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	82
Nuclear fuel inventory, net	196
Property, plant and equipment, net	1,380
Construction work in progress	30
Asset retirement obligation	(585)
LaSalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	105
Nuclear fuel inventory, net	244
Property, plant and equipment, net	1,610
Construction work in progress	12
Asset retirement obligation	(975)
Braidwood LaSalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	187
Nuclear fuel inventory, net	440
Property, plant and equipment, net	2,990
Construction work in progress	42
Asset retirement obligation	(1,560)
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	986	978
Property, plant and equipment, net	19,837	$ 22,214
Exelon Generation Co L L C [Member] \| Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	82
Nuclear fuel inventory, net	196
Property, plant and equipment, net	1,380
Construction work in progress	30
Asset retirement obligation	(585)
Exelon Generation Co L L C [Member] \| LaSalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	105
Nuclear fuel inventory, net	244
Property, plant and equipment, net	1,610
Construction work in progress	12
Asset retirement obligation	(975)
Exelon Generation Co L L C [Member] \| Braidwood LaSalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	187
Nuclear fuel inventory, net	440
Property, plant and equipment, net	2,990
Construction work in progress	42
Asset retirement obligation	$ (1,560)

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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