Leases - Lease Assets and Liabilities Included in the Consolidated Statement of Financial Position (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease right-of-use assets	$ 335	$ 334
Operating lease liabilities - current	89	95
Operating lease liabilities - noncurrent	246	244
Present value of lease liabilities	$ 335	$ 339
Operating lease right of use asset, statement of financial position, extensible list	Other noncurrent liabilities	Other noncurrent liabilities
Operating lease liability, current, statement of financial position, extensible list	Other current liabilities	Other current liabilities
Operating lease liability, noncurrent, statement of financial position, extensible list	Other noncurrent liabilities	Other noncurrent liabilities
Weighted average remaining lease term:
Operating leases	6 years	5 years
Weighted average discount rate:
Operating leases	5.20%	5.90%