Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Leased Assets [Line Items]
Operating Lease, Cost	$ 399
Variable Lease, Cost	145
Lease, Cost	$ 544
Operating Leases, Rent Expense		$ 452	$ 408
Operating Lease, Weighted Average Remaining Lease Term	6 years
Operating Lease, Weighted Average Discount Rate, Percent	2.20%
Operating Lease, Payments	$ 397
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	467
Lessee, Operating Lease, Liability, to be Paid, Year One	352
Lessee, Operating Lease, Liability, to be Paid, Year Two	279
Lessee, Operating Lease, Liability, to be Paid, Year Three	191
Lessee, Operating Lease, Liability, to be Paid, Year Four	143
Lessee, Operating Lease, Liability, to be Paid, Year Five	91
Lessee, Operating Lease, Liability, to be Paid, after Year Five	235
Lessee, Operating Lease, Liability, to be Paid	1,291
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(84)
Operating Lease, Liability	1,207
Operating Leases, Future Minimum Payments Due, Next Twelve Months		352
Operating Leases, Future Minimum Payments, Due in Two Years		287
Operating Leases, Future Minimum Payments Receivable, in Three Years		200
Operating Leases, Future Minimum Payments, Due in Four Years		111
Operating Leases, Future Minimum Payments, Due in Five Years		71
Operating Leases, Future Minimum Payments, Due Thereafter		172
Operating Leases, Future Minimum Payments Due		$ 1,193
Other noncurrent assets
Operating Leased Assets [Line Items]
Operating Lease, Right-of-Use Asset	1,190
Other current liabilities
Operating Leased Assets [Line Items]
Operating Lease, Liability, Current	332
Other Noncurrent Liabilities [Member]
Operating Leased Assets [Line Items]
Operating Lease, Liability, Noncurrent	$ 875