Leases - Additional Information (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) option_to_renew
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 114
Weighted average remaining lease term (in years)	6 years
Weighted average discount rate	2.29%
Operating leases, not yet commenced, lease obligations	$ 466
Minimum
Lessee, Lease, Description [Line Items]
Number of renewal options | option_to_renew	1
Operating leases, non-cancellable lease terms	1 year
Maximum
Lessee, Lease, Description [Line Items]
Operating leases, non-cancellable lease terms	15 years