Basis of Presentation and Summary of Significant Accounting Policies - VIE (Details) - USD ($) $ in Millions	Jun. 30, 2019	Sep. 30, 2018
Variable Interest Entity [Line Items]
Total assets	$ 288	$ 313
Total liabilities	240	252
Current assets
Variable Interest Entity [Line Items]
Total assets	249	270
Noncurrent assets
Variable Interest Entity [Line Items]
Total assets	39	43
Current liabilities
Variable Interest Entity [Line Items]
Total liabilities	$ 240	$ 252