Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 31, 2015
Class Of Stock [Line Items]
Repurchase authorization, shares			5,000,000
Cash dividends paid to common stockholders	$ 39	$ 38
Cash dividend paid per share	$ 0.63	$ 0.60
Dividends paid to noncontrolling interests	$ 6	$ 2
January 2015 Share Repurchase Authorization [Member]
Class Of Stock [Line Items]
Common stock shares repurchased under the current authorization	3,491,902
Shares remaining available for repurchase under the current authorization	1,508,098