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Debt and Other Obligations Lease/Leaseback Obligations (Details) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2053 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2022
Sale Leaseback Transaction [Line Items]
CT and QTE outstanding leaseback obligation	$ 0		$ 0
Leasing transaction, number of units						16
Leasing transaction, number of units						16
CT and QTE outstanding leaseback obligation	0		0
Lagoon Creek
Sale Leaseback Transaction [Line Items]
Amortization of reacquired rights	2
Lagoon Creek | Forecast
Sale Leaseback Transaction [Line Items]
Amortization of reacquired rights		$ 1		$ 2	$ 5
Kemper/Lagoon Creek leasehold interests
Sale Leaseback Transaction [Line Items]
leasehold interest	155
leasehold interest	$ 155
Lagoon Creek
Sale Leaseback Transaction [Line Items]
leasehold interest			78
leasehold interest			78
Kemper
Sale Leaseback Transaction [Line Items]
leasehold interest			77
leasehold interest			$ 77
Kemper/Lagoon Creek leasehold interests
Sale Leaseback Transaction [Line Items]
Leasing transaction, number of units						8
Leasing transaction, number of units						8

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- Definition

Amortization of reacquired rights

+ References

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- Definition

The outstanding leaseback obligations related to combustion turbine units and qualified technological equipment and software.

+ References

No definition available.

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- Definition

The number of units involved in leaseback transactions.

+ References

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- Definition

leasehold interest

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481295/840-40-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479741/842-40-50-2

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