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 accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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Current portion of 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 asset retirement obligations incurred during the period.

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount classified as liabilities attributable to disposal group held for sale or disposed of, expected to be disposed of within one year or the normal operating cycle, if longer.

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Nuclear Decommissioning - Rollforward of Nuclear Decommissioning ARO (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense		$ 250	$ 242
Asset Retirement Obligation, Revision of Estimate	$ 330
Liabilities held for sale		764		$ 777
Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear decommissioning ARO, beginning balance	10,005	10,005
Accretion expense		243
Asset Retirement Obligation, Revision of Estimate		232
Costs incurred related to decommissioning plants		(43)
Nuclear decommissioning ARO, ending balance		10,437
Current portion of ARO		99		22
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense		248	$ 242
Asset Retirement Obligation, Revision of Estimate	330
Liabilities held for sale		764		777
Exelon Generation Co L L C [Member] \| Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear decommissioning ARO, beginning balance	$ 10,005	10,005
Accretion expense		243
Asset Retirement Obligation, Revision of Estimate		232
Costs incurred related to decommissioning plants		(43)
Nuclear decommissioning ARO, ending balance		10,437
Current portion of ARO		99		22
Nuclear Decommissioning Asset Retirement Obligation [Member] \| Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities held for sale		755		772
Nuclear Decommissioning Asset Retirement Obligation [Member] \| Exelon Generation Co L L C [Member] \| Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities held for sale		$ 755		$ 772