Stock Repurchase Program - Additional Information (Detail) - USD ($)			1 Months Ended			3 Months Ended					6 Months Ended		9 Months Ended
	Aug. 15, 2016	Dec. 09, 2015	May 24, 2016	Apr. 30, 2016	Aug. 31, 2015	Aug. 15, 2016	Jul. 31, 2016		Jan. 31, 2016	Jul. 31, 2015	May 24, 2016	Jan. 31, 2016	Jul. 31, 2016		Jul. 31, 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
Remaining amount available for further repurchases							$ 175,000,000						$ 175,000,000
Shares repurchased (in shares)							2,525,000	[1]		678,000			6,889,000	[1]	3,968,000
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)												2,100,000
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	$ 20,000,000
Average purchase price of shares purchased under agreement											$ 44.40
Shares repurchased (in shares)											4,500,000
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] | Accelerated Share Repurchase Program May 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, prepayment during prior period, derivative settlement	$ 25,000,000
Average purchase price of shares purchased under agreement						$ 52.98
Shares repurchased (in shares)	351,170					2,400,000

[1] Does not include the 351,170 shares and $25.0 million equity forward contract, respectively, from the May 2016 ASR settled in August 2016.