Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	$ 1,463	$ 1,456
Property, plant and equipment, net	81,017	80,233
Dresden [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	68
Nuclear fuel inventory, net	204
Property, plant and equipment, net	1,084
Construction work in progress	16
Asset retirement obligation	(1,301)
Byron [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	68
Nuclear fuel inventory, net	172
Property, plant and equipment, net	1,343
Construction work in progress	22
Asset retirement obligation	(596)
Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	81
Nuclear fuel inventory, net	203
Property, plant and equipment, net	1,390
Construction work in progress	32
Asset retirement obligation	(554)
Dresden Byron Braidwood [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory, net	217
Nuclear fuel inventory, net	579
Property, plant and equipment, net	3,817
Construction work in progress	70
Asset retirement obligation	(2,451)
Mystic Generating Station [Member] \| Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory	32
Fuel inventory	12
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]
Materials and supplies inventory, net	1,038	1,026
Property, plant and equipment, net	24,169	$ 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	68
Nuclear fuel inventory, net	204
Property, plant and equipment, net	1,084
Construction work in progress	16
Asset retirement obligation	(1,301)
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	68
Nuclear fuel inventory, net	172
Property, plant and equipment, net	1,343
Construction work in progress	22
Asset retirement obligation	(596)
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	81
Nuclear fuel inventory, net	203
Property, plant and equipment, net	1,390
Construction work in progress	32
Asset retirement obligation	(554)
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	217
Nuclear fuel inventory, net	579
Property, plant and equipment, net	3,817
Construction work in progress	70
Asset retirement obligation	(2,451)
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	32
Fuel inventory	12
Property, plant and equipment, net	902
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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