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Asset Retirement Obligations (Details) - USD ($)	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2019
Asset Retirement Obligations
Asset Retirement Obligation, Period Increase (Decrease)		$ 455,000,000
Amortization and Depreciation of Decontaminating and Decommissioning Assets		127,000,000
Balance at September 30, 2019		5,616,000,000
Settlements		(85,000,000)
Asset Retirement Obligation, Revision of Estimate		387,000,000
Accretion (recorded as regulatory asset)		153,000,000
Balance at June 30, 2020	$ 6,071,000,000	6,071,000,000
Non-nuclear Operating
Asset Retirement Obligations
Asset Retirement Obligation, Revision of Estimate		38,000,000
Nuclear
Asset Retirement Obligations
Balance at September 30, 2019		3,136,000,000
Settlements		0
Asset Retirement Obligation, Revision of Estimate		0
Accretion (recorded as regulatory asset)		106,000,000
Balance at June 30, 2020	3,242,000,000	3,242,000,000
Non-nuclear
Asset Retirement Obligations
Balance at September 30, 2019		2,480,000,000
Settlements		(85,000,000)
Asset Retirement Obligation, Revision of Estimate		387,000,000
Accretion (recorded as regulatory asset)		47,000,000
Balance at June 30, 2020	2,829,000,000	2,829,000,000
Asset Retirement Obligation, Revision of Estimate		129,000,000
Non-nuclear Closed Activities
Asset Retirement Obligations
Asset Retirement Obligation, Revision of Estimate		91,000,000
Allen Fossil Plant [Member]
Asset Retirement Obligations
Asset Retirement Obligation, Revision of Estimate	267
Accounts payable and accrued liabilities
Asset Retirement Obligations
Current portion of ARO	$ (266,000,000)	$ (266,000,000)	$ (163,000,000)

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The amount of accretion recorded as a regulatory asset during the period.

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Increase in Asset Retirement Obligation, Revisions in Estimate

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Reconciliation of Asset Retirement Obligations [Line Items]

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The current period expense charged against earnings on decontaminating and decommissioning of facilities used in the normal conduct of business and not intended for resale to allocate or recognize the cost of the assets over their useful lives.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
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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.

+ References

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-SubTopic 20
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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of increase (decrease) in asset retirement obligations.

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-Topic 410
-SubTopic 20
-Section 50
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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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-Topic 410
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