Stock Repurchase Program - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		4 Months Ended
	Feb. 17, 2017	Jan. 31, 2017	Jan. 31, 2016	Feb. 17, 2017	Aug. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount		$ 500,000,000			$ 500,000,000
Remaining amount available for further repurchases		$ 335,500,000
Shares repurchased (in shares)		1,393,000	3,849,000
Accelerated Share Repurchase Program December 2016 [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
Subsequent Event [Member] | Accelerated Share Repurchase Program December 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, prepayment during prior period, derivative settlement	$ 20,000,000
Average purchase price of shares purchased under agreement				$ 60.53
Shares repurchased (in shares)	258,710			1,700,000