Leases - Assets and Liabilities Lessee (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
ROU assets:
Operating lease ROU assets	$ 390	$ 415
Finance lease ROU assets	49	52
Total ROU assets	$ 439	$ 467
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other Assets, Noncurrent	Other Assets, Noncurrent
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Carrying value	Carrying value
Lease liabilities:
Operating lease liabilities — current	$ 81	$ 87
Operating lease liabilities — noncurrent	318	334
Finance lease liabilities — current	4	5
Finance lease liabilities — noncurrent	41	41
Total lease liabilities	$ 444	$ 467
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other noncurrent liabilities	Other noncurrent liabilities
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current maturities of long-term debt	Current maturities of long-term debt
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term Debt and Lease Obligation	Long-term Debt and Lease Obligation