Commitments and Contingencies - Membership Interests of VIE Subject to Mandatory Redemption (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Long-term Purchase Commitment [Line Items]
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	$ 18	$ 19
Minimum payments on membership interests subject to mandatory redemption, due in next twelve months	1
Minimum payments on membership interests subject to mandatory redemption, due in year two	1
Minimum payments on membership interests subject to mandatory redemption, due in year three	1
Minimum payments on membership interests subject to mandatory redemption, due in year four	2
Minimum payments on membership interests subject to mandatory redemption, due in year five	$ 2