Stock Repurchase Program - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended			4 Months Ended		6 Months Ended
	May 19, 2017	Feb. 17, 2017	Apr. 30, 2017	Jan. 31, 2017	Apr. 30, 2016	May 19, 2017	Feb. 17, 2017	Apr. 30, 2017	Apr. 30, 2016	Aug. 31, 2016
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			$ 235,500,000					$ 235,500,000
Shares repurchased (in shares)			1,381,000		515,000			2,775,000	4,364,000
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
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)							1,700,000
Accelerated Share Repurchase Program February 2017 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount			$ 100,000,000					$ 100,000,000
Prepayment amount			100,000,000
Accelerated share repurchase, initial share delivery, amount			$ 80,000,000					$ 80,000,000
Subsequent Event | Accelerated Share Repurchase Program February 2017 [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						$ 72.02
Shares repurchased (in shares)	265,894					1,400,000