Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions		1 Months Ended	3 Months Ended
	Oct. 30, 2015	Aug. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	May. 31, 2013
Class of Stock [Line Items]
Aggregate cost of shares repurchased			$ 13,000,000	$ 0
Dividend declaration date			2015-08
Dividend payable date			Oct. 21, 2015
Dividend record date			Sep. 16, 2015
Subsequent Event [Member]
Class of Stock [Line Items]
Remaining authorized amount under stock repurchase program	$ 452,000,000
Class A Common Stock [Member]
Class of Stock [Line Items]
Aggregate amount of shares authorized to be repurchased					$ 500,000,000
Cash dividend declared		$ 0.10
Class A Common Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Number of shares repurchased	3.3
Aggregate cost of shares repurchased	$ 48,000,000
Class B Common Stock [Member]
Class of Stock [Line Items]
Cash dividend declared		$ 0.10