Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Operating Leased Assets [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	7 years	6 years
Operating Lease, Weighted Average Discount Rate, Percent	1.80%	2.20%
Operating Lease, Payments	$ 398	$ 397
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	515	467
Operating Lease, Cost	384	399
Variable Lease, Cost	130	145
Lease, Cost	$ 514	$ 544
Operating Leases, Rent Expense			$ 452
Operating Lease, Weighted Average Remaining Lease Term	7 years	6 years
Operating Lease, Weighted Average Discount Rate, Percent	1.80%	2.20%
Operating Lease, Payments	$ 398	$ 397
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	515	467
Lessee, Operating Lease, Liability, to be Paid, Year One	337
Lessee, Operating Lease, Liability, to be Paid, Year Two	275
Lessee, Operating Lease, Liability, to be Paid, Year Three	226
Lessee, Operating Lease, Liability, to be Paid, Year Four	164
Lessee, Operating Lease, Liability, to be Paid, Year Five	115
Lessee, Operating Lease, Liability, to be Paid, after Year Five	353
Lessee, Operating Lease, Liability, to be Paid	1,470
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(96)
Operating Lease, Liability	1,374
Other noncurrent assets
Operating Leased Assets [Line Items]
Operating Lease, Right-of-Use Asset	1,376	1,190
Other current liabilities
Operating Leased Assets [Line Items]
Operating Lease, Liability, Current	319	332
Other Noncurrent Liabilities
Operating Leased Assets [Line Items]
Operating Lease, Liability, Noncurrent	$ 1,055	$ 875