Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Numerator
Net income	$ 67	$ 71	$ 57	$ 143
Denominator
Weighted-average shares used to compute basic EPS (shares)	200	205	201	205
Dilutive effect of share-based awards (shares)	0	0	1	0
Weighted-average shares used to compute diluted EPS (shares)	200	205	202	205
Earnings per share
Basic (usd per share)	$ 0.33	$ 0.35	$ 0.28	$ 0.70
Diluted (usd per share)	$ 0.33	$ 0.35	$ 0.28	$ 0.70
Stock Compensation Plan
Earnings per share
Common shares related to stock-based compensation excluded from diluted earnings per share calculation due to anti-dilutive effect (shares)	0	0	0	0