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Subsequent Events (Details) - USD ($) $ in Millions	Sep. 30, 2025	Oct. 02, 2024	Sep. 30, 2024	Sep. 30, 2013	Sep. 30, 2012
Debt Instrument, Redemption [Line Items]
Non-current regulatory liabilities	$ 141		$ 83
Regulatory assets	8,047		9,408
Face Amount	40			$ 360
Long-term debt of variable interest entities, net	1,632		897
Current maturities of long-term debt of variable interest entities issued at par	49		37
JACTG
Debt Instrument, Redemption [Line Items]
Face Amount		$ 720
Variable Interest Entity, Primary Beneficiary [Member]
Debt Instrument, Redemption [Line Items]
Debt and Lease Obligation		$ 800	0
Holdco
Debt Instrument, Redemption [Line Items]
Face Amount					$ 100
Unrealized gains/losses on commodity derivatives
Debt Instrument, Redemption [Line Items]
Regulatory assets	12		64
Unrealized gains/losses on commodity derivatives
Debt Instrument, Redemption [Line Items]
Non-current regulatory liabilities	$ 10		$ 2