Stock Repurchase Program - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands		1 Months Ended			3 Months Ended			6 Months Ended
	Dec. 09, 2015	May. 24, 2016	Apr. 30, 2016	Aug. 31, 2015	Aug. 15, 2016	Apr. 30, 2016	Apr. 30, 2015	May. 24, 2016	Apr. 30, 2016		Jan. 31, 2016	Apr. 30, 2015	Sep. 01, 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount			$ 500,000,000			$ 500,000,000			$ 500,000,000				$ 500,000,000
Remaining amount available for further repurchases			300,000,000			$ 300,000,000			$ 300,000,000
Shares repurchased (in shares)						515	0		4,364	[1]		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
Stock Repurchase Program, Prepayment During Prior Period, Derivative Settlement			$ 20,000,000
Subsequent Event [Member] | Accelerated Share Repurchase Program December 2015 [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								$ 44.40
Shares repurchased (in shares)		517						4,500
Subsequent Event [Member] | Accelerated Share Repurchase Program May 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount		$ 125,000,000						$ 125,000,000
Prepayment amount		125,000,000
Accelerated Share Repurchase, Initial Share Delivery, Amount		$ 100,000,000						$ 100,000,000
Subsequent Event [Member] | Scenario, Forecast [Member] | Accelerated Share Repurchase Program May 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Accelerated Share Repurchases, Remaining Agreement Amount					$ 25,000,000

[1] Does not include the final 517,410 shares and $20.0 million equity forward contract, respectively, from the December 2015 ASRs settled in May 2016.