Stock Repurchase Program - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands		1 Months Ended	3 Months Ended		5 Months Ended	6 Months Ended
	Dec. 09, 2015	Aug. 31, 2015	Jan. 31, 2016	Jan. 31, 2015	Apr. 30, 2016	Jan. 31, 2016	Sep. 01, 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount			$ 500,000,000			$ 500,000,000	$ 500,000,000
Remaining amount available for further repurchases			$ 300,000,000			$ 300,000,000
Shares repurchased (in shares)			3,849	3,290
Accelerated Share Repurchase Program August 2015 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount		$ 100,000,000
Prepayment amount		100,000,000
Accelerated Share Repurchase, Initial Share Delivery, Amount		$ 80,000,000
Stock Repurchase Program, Prepayment During Prior Period, Derivative Settlement			$ 20,000,000
Average purchase price of shares purchased under agreement						$ 48.06
Shares repurchased (in shares)						2,100
Accelerated Share Repurchase Program December 2015 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount	$ 200,000,000
Prepayment amount	200,000,000
Accelerated Share Repurchase, Initial Share Delivery, Amount	$ 160,000,000
Average purchase price of shares purchased under agreement	$ 46.08
Scenario, Forecast [Member] | Accelerated Share Repurchase Program December 2015 [Member]
Equity, Class of Treasury Stock [Line Items]
Accelerated Share Repurchases, Remaining Agreement Amount					$ 40,000,000