Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Operating Leases
Operating lease right-of-use assets	$ 275	$ 273
Operating lease liabilities, current	41	39
Operating lease liabilities, noncurrent	298	299
Total operating lease liabilities	$ 339	$ 338
Weighted Average Remaining Lease Term
Operating leases	8 years	8 years
Weighted Average Discount Rate
Operating leases	4.58%	4.58%