Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2020
Numerator
Net income	$ 97	$ 68	$ 87	$ 59	$ 63	$ 73	$ 252	$ 195
Denominator
Weighted-average common shares outstanding (shares)	182			186			183	187
Effect of potentially dilutive securities (shares)	1			0			1	1
Weighted average diluted shares outstanding (shares)	183			186			184	188
Earnings per share
Basic (usd per share)	$ 0.53			$ 0.32			$ 1.38	$ 1.04
Diluted (usd per share)	$ 0.53			$ 0.32			$ 1.37	$ 1.04
Shares excluded from diluted earnings per share calculation due to anti-dilutive effect (shares)				2				1