Leases - Component of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Leases [Abstract]
Operating lease cost	$ 104	$ 96	$ 101
Finance lease cost:
Amortization of ROU assets	3	4	4
Interest on lease liabilities	3	3	3
Variable lease cost	2	6	4
Short-term lease cost	4	2	2
Total lease cost	116	111	114
Cash paid related to lease liabilities:
Operating cash flows — operating leases	103	95	99
Operating cash flows — finance leases	3	3	3
Financing cash flows — finance leases	1	2	3
Non-cash lease liability activities:
ROU assets obtained in exchange for operating lease liabilities	136	72	85
ROU assets obtained in exchange for finance lease liabilities	$ 6	$ 2	$ 1
Weighted-average remaining lease term (in years)
Operating leases	7 years 1 month 6 days	6 years
Finance leases	5 years 3 months 18 days	3 years 8 months 12 days
Weighted-average discount rate (%)
Operating leases	4.50%	3.60%
Finance leases	2.20%	1.80%