Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Implications of Potential Early Plant Retirement [Line Items]
Fuel inventory	$ 312	$ 334
Property, plant and equipment, net	80,233	76,707
Mystic Generating Station [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory	31
Fuel inventory	11
Property, plant and equipment, net	902
Asset retirement obligation	(3)
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Property, plant and equipment, net	24,193	$ 23,981
Exelon Generation Co L L C [Member] \| Mystic Generating Station [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory	31
Fuel inventory	11
Property, plant and equipment, net	902
Asset retirement obligation	$ (3)

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- Definition

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 fossil fuel included in inventory classified as other.

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Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

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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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