Asset Retirement Obligations (Details) - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2021	Sep. 30, 2020
Asset Retirement Obligations
Asset Retirement Obligation, Period Increase (Decrease)	$ 133
Amortization and Depreciation of Decontaminating and Decommissioning Assets	36
Asset Retirement Obligation, Beginning Balance	6,785
Settlements	(80)
Asset Retirement Obligation, Revision of Estimate	108
Accretion (recorded as regulatory asset)	105
Asset Retirement Obligation, Ending Balance	6,918
Current portion of ARO	(271)	$ (345)
Nuclear
Asset Retirement Obligations
Asset Retirement Obligation, Beginning Balance	3,278
Settlements	(3)
Asset Retirement Obligation, Revision of Estimate	2
Accretion (recorded as regulatory asset)	74
Asset Retirement Obligation, Ending Balance	3,351
Non-nuclear
Asset Retirement Obligations
Asset Retirement Obligation, Beginning Balance	3,507
Settlements	(77)
Asset Retirement Obligation, Revision of Estimate	106
Accretion (recorded as regulatory asset)	31
Asset Retirement Obligation, Ending Balance	$ 3,567
Accounts payable and accrued liabilities
Asset Retirement Obligations
Current portion of ARO		$ (345)

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

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- Definition

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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- 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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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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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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of increase (decrease) in asset retirement obligations.

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

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-Publisher FASB
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-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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