Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions		1 Months Ended	3 Months Ended
	Nov. 02, 2018	Aug. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	May 31, 2013
Class of Stock [Line Items]
Cash dividends declared per share of common stock			$ 0.10	$ 0.10
Cash dividends per common share, date of dividend payable		Oct. 17, 2018
Cash dividends per common share, date of record for dividend		Sep. 12, 2018
Subsequent Event [Member]
Class of Stock [Line Items]
Remaining authorized amount under stock repurchase program	$ 429,000,000
Class A Common Stock [Member]
Class of Stock [Line Items]
Aggregate amount of shares authorized to be repurchased					$ 500,000,000
Number of shares repurchased			0.0
Cash dividends declared per share of common stock		$ 0.10
Class A Common Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Number of shares repurchased	5.2
Aggregate cost of shares repurchased	$ 71,000,000
Class B Common Stock [Member]
Class of Stock [Line Items]
Cash dividends declared per share of common stock		$ 0.10