Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Numerator
Net income	$ 420	$ 317	$ 208
Denominator
Weighted-average shares common shares outstanding (in shares)	182,000	187,000	189,000
Effect of potentially dilutive securities (in shares)	1,000	1,000	0
Weighted-average diluted shares outstanding (in shares)	183,000	188,000	189,000
Earnings per share
Earnings per share, basic (usd per share)	$ 2.30	$ 1.70	$ 1.10
Earnings per share, diluted (usd per share)	$ 2.29	$ 1.69	$ 1.10
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		1,000	1,000