Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018
Numerator
Net income	$ 65	$ 63	$ 53	$ 64	$ 67	$ (10)	$ 181	$ 121
Denominator
Weighted-average common shares outstanding (shares)	189			195			189	199
Effect of potentially dilutive securities (shares)	0			1			0	1
Weighted average diluted shares outstanding (shares)	189			196			189	200
Earnings per share
Basic (usd per share)	$ 0.34			$ 0.33			$ 0.96	$ 0.61
Diluted (usd per share)	$ 0.34			$ 0.33			$ 0.96	$ 0.61
Shares excluded from diluted earnings per share calculation due to anti-dilutive effect (shares)	1						2