Leases - Components of Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Operating lease cost	$ 111	$ 108	$ 108
Short-term lease cost	26	29	29
Total lease cost	$ 137	$ 137	$ 137