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Asset Retirement Obligations (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2019	Sep. 30, 2018
Asset Retirement Obligations
Asset Retirement Obligation, Period Increase (Decrease)	$ 198
Amortization and Depreciation of Decontaminating and Decommissioning Assets	72
Balance at September 30, 2018	4,779
Settlements	(42)
Asset Retirement Obligation, Revision of Estimate	136
Accretion (recorded as regulatory asset)	90
Balance at March 31, 2019	4,977
Asset Retirement Obligation, Liabilities Incurred	14
Nuclear
Asset Retirement Obligations
Balance at September 30, 2018	2,989
Settlements	0
Asset Retirement Obligation, Revision of Estimate	0
Accretion (recorded as regulatory asset)	67
Balance at March 31, 2019	3,070
Asset Retirement Obligation, Liabilities Incurred	14
Non-nuclear
Asset Retirement Obligations
Balance at September 30, 2018	1,790
Settlements	(42)
Asset Retirement Obligation, Revision of Estimate	136
Accretion (recorded as regulatory asset)	23
Balance at March 31, 2019	1,907
Asset Retirement Obligation, Revision of Estimate	103
Asset Retirement Obligation, Liabilities Incurred	0
Non-nuclear
Asset Retirement Obligations
Asset Retirement Obligation, Revision of Estimate	33
Accounts payable and accrued liabilities
Asset Retirement Obligations
Current portion of ARO	$ 102	$ 115

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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=109223946&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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
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Amount of asset retirement obligations incurred during the period.

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-Publisher FASB
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-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
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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.

+ References

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-Publisher FASB
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-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
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Amount of increase (decrease) in asset retirement obligations.

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-Topic 410
-SubTopic 20
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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

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-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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