Leases - Component of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Leases [Abstract]
Operating lease cost	$ 111	$ 104	$ 96
Finance lease cost:
Amortization of ROU assets	4	3	4
Interest on lease liabilities	3	3	3
Variable lease cost	1	2	6
Short-term lease cost	10	4	2
Total lease cost	129	116	111
Cash paid related to lease liabilities:
Operating cash flows — operating leases	109	103	95
Operating cash flows — finance leases	4	3	3
Financing cash flows — finance leases	2	1	2
Non-cash lease liability activities:
ROU assets obtained in exchange for operating lease liabilities	84	136	72
ROU assets obtained in exchange for finance lease liabilities	$ 7	$ 6	$ 2
Weighted-average remaining lease term (in years)
Operating leases	6 years 9 months 18 days	7 years 1 month 6 days
Finance leases	6 years 8 months 12 days	5 years 3 months 18 days
Weighted-average discount rate (%)
Operating leases	4.80%	4.50%
Finance leases	6.90%	2.20%