Leases (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Lessee, Lease, Description [Line Items]
Right-of-use assets obtained in exchange for operating lease liabilities	$ 55	$ 175
Other Noncurrent Assets
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset	1,341		$ 1,376
Other Current Liabilities
Lessee, Lease, Description [Line Items]
Operating lease liabilities - current	314		319
Other Noncurrent Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating lease liabilities - noncurrent	$ 1,022		$ 1,055