Income Taxes - Income Before Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Domestic	$ 424	$ 330	$ 576
Foreign	243	71	279
Income before income taxes	$ 667	$ 401	$ 855