Leases (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Lessee, Lease, Description [Line Items]
Right-of-use assets obtained in exchange for operating lease liabilities	$ 411	$ 315
Other Noncurrent Assets
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset	1,369		$ 1,190
Other Current Liabilities
Lessee, Lease, Description [Line Items]
Operating lease liabilities - current	323		332
Other Noncurrent Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating lease liabilities - noncurrent	$ 1,058		$ 875