Stock Repurchase Program - Additional Information (Detail) $ / shares in Units, shares in Thousands	1 Months Ended						2 Months Ended	3 Months Ended					4 Months Ended	9 Months Ended
	May 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Feb. 28, 2018 USD ($)	Dec. 31, 2017 USD ($) share_repurchase_program	Nov. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Nov. 01, 2018 USD ($)	Jul. 31, 2018 USD ($) shares	Apr. 30, 2018 USD ($) $ / shares shares	Jan. 31, 2018 USD ($)	Nov. 30, 2017 $ / shares shares	Jul. 31, 2017 shares	Mar. 31, 2018 $ / shares shares	Jul. 31, 2018 USD ($) shares	Jul. 31, 2017 shares	Apr. 05, 2018 USD ($)
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								$ 325,000,000						$ 325,000,000
Shares repurchased (in shares) | shares								1,509				1,627		4,411	4,401
Accelerated Share Repurchase Program September 2017
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount						$ 100,000,000.0
Prepayment amount						100,000,000.0
Accelerated share repurchase, initial share delivery, amount						$ 80,000,000.0
Stock repurchase program, prepayment during prior period, derivative settlement					$ 20,000,000.0					$ 20,000,000.0
Shares repurchased (in shares) | shares											1,200
Average purchase price of shares purchased under agreement (in USD per share) | $ / shares											$ 83.80
Accelerated Share Repurchase Program December 2017
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount				$ 200,000,000.0
Prepayment amount				200,000,000.0
Accelerated share repurchase, initial share delivery, amount				$ 160,000,000.0
Stock repurchase program, prepayment during prior period, derivative settlement		$ 20,000,000.0	$ 20,000,000
Shares repurchased (in shares) | shares													2,300
Average purchase price of shares purchased under agreement (in USD per share) | $ / shares													$ 87.08
Accelerated share repurchase programs entered into | share_repurchase_program				2
Accelerated Share Repurchase Program May 2018
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount	$ 165,000,000.0
Prepayment amount	165,000,000.0
Accelerated share repurchase, initial share delivery, amount	$ 132,000,000.0
Open Market Share Repurchase
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares) | shares									400
Average purchase price of shares purchased under agreement (in USD per share) | $ / shares									$ 82.61
Stock repurchased during period, value									$ 35,000,000
Scenario, Forecast | Accelerated Share Repurchase Program May 2018
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, prepayment during prior period, derivative settlement							$ 33,000,000.0