Basis of Presentation and Summary of Significant Accounting Policies - VIE (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Variable Interest Entity [Line Items]
Total assets	$ 276	$ 313
Total liabilities	235	252
Current Assets
Variable Interest Entity [Line Items]
Total assets	236	270
Noncurrent Assets
Variable Interest Entity [Line Items]
Total assets	40	43
Current Liabilities
Variable Interest Entity [Line Items]
Total liabilities	$ 235	$ 252