Leases - Component of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease cost	$ 101	$ 102
Finance lease cost:
Amortization of ROU assets	4	5
Interest on lease liabilities	3	3
Variable lease cost	4	5
Short-term lease cost	2	3
Total lease cost	114	118
Cash paid related to lease liabilities:
Operating cash flows — operating leases	99	103
Operating cash flows — finance leases	3	3
Financing cash flows — finance leases	3	4
Non-cash lease liability activities:
ROU assets obtained in exchange for operating lease liabilities	85	506
ROU assets obtained in exchange for finance lease liabilities	$ 1	$ 22
Weighted-average remaining lease term (in years)
Operating leases	6 years 3 months 18 days	6 years 2 months 12 days
Finance leases	2 years 4 months 24 days	2 years 4 months 24 days
Weighted-average discount rate (%)
Operating leases	3.60%	3.80%
Finance leases	1.50%	1.90%