Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	$ 1,508	$ 1,456
Property, plant and equipment, net	81,748	80,233
Dresden [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	70
Nuclear fuel inventory, net	182
Property, plant and equipment, net	1,057
Construction work in progress	18
Asset retirement obligation	(1,317)
Byron [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	70
Nuclear fuel inventory, net	145
Property, plant and equipment, net	1,334
Construction work in progress	21
Asset retirement obligation	(604)
Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	82
Nuclear fuel inventory, net	180
Property, plant and equipment, net	1,416
Construction work in progress	18
Asset retirement obligation	(562)
Lasalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Inventory, Raw Materials, Net of Reserves	108
Nuclear fuel inventory, net	244
Property, plant and equipment, net	1,588
Construction work in progress	19
Asset retirement obligation	(915)
Dresden Byron Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	330
Nuclear fuel inventory, net	751
Property, plant and equipment, net	5,395
Construction work in progress	76
Asset retirement obligation	(3,398)
Mystic Generating Station [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	33
Fuel inventory	6
Property, plant and equipment, net	898
Asset retirement obligation	(3)
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	1,075	1,026
Property, plant and equipment, net	23,954	$ 24,193
Exelon Generation Co L L C [Member] \| Dresden [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	70
Nuclear fuel inventory, net	182
Property, plant and equipment, net	1,057
Construction work in progress	18
Asset retirement obligation	(1,317)
Exelon Generation Co L L C [Member] \| Byron [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	70
Nuclear fuel inventory, net	145
Property, plant and equipment, net	1,334
Construction work in progress	21
Asset retirement obligation	(604)
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	180
Property, plant and equipment, net	1,416
Construction work in progress	18
Asset retirement obligation	(562)
Exelon Generation Co L L C [Member] \| Dresden Byron Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	330
Nuclear fuel inventory, net	751
Property, plant and equipment, net	5,395
Construction work in progress	76
Asset retirement obligation	(3,398)
Exelon Generation Co L L C [Member] \| Mystic Generating Station [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Inventory, Raw Materials, Gross	33
Fuel inventory	6
Property, plant and equipment, net	898
Asset retirement obligation	$ (3)

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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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