Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	$ 1,405	$ 1,456
Property, plant and equipment, net	82,561	80,233
Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	82
Nuclear fuel inventory, net	147
Property, plant and equipment, net	1,403
Construction work in progress	18
Asset retirement obligation	(570)
Lasalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Inventory, Raw Materials, Net of Reserves	107
Nuclear fuel inventory, net	218
Property, plant and equipment, net	1,571
Construction work in progress	23
Asset retirement obligation	(926)
Dresden Byron Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	189
Nuclear fuel inventory, net	365
Property, plant and equipment, net	2,974
Construction work in progress	41
Asset retirement obligation	(1,496)
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	971	1,026
Property, plant and equipment, net	23,709	$ 24,193
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	147
Property, plant and equipment, net	1,403
Construction work in progress	18
Asset retirement obligation	(570)
Exelon Generation Co L L C [Member] \| Lasalle [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Inventory, Raw Materials, Net of Reserves	107
Nuclear fuel inventory, net	218
Property, plant and equipment, net	1,571
Construction work in progress	23
Asset retirement obligation	(926)
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	189
Nuclear fuel inventory, net	365
Property, plant and equipment, net	2,974
Construction work in progress	41
Asset retirement obligation	$ (1,496)

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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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Aggregated amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed. This amount is net of valuation reserves and adjustments.

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of unprocessed items to be consumed in the manufacturing or production process.

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The carrying amount as of the balance sheet of nuclear fuel held as property plant and equipment. This amount is net of amortization based on the energy produced over the life of the fuel.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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