Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Operating Leases
Operating lease right-of-use assets	$ 289
Operating lease liabilities, current	38
Operating lease liabilities, noncurrent	321	$ 0
Total operating lease liabilities	$ 359
Weighted Average Remaining Lease Term
Operating leases	9 years
Weighted Average Discount Rate
Operating leases	4.55%